The Altus Metrum System
An Owner's Manual for TeleMetrum, TeleMini and TeleDongle Devices
Bdale
Garbee
Keith
Packard
Bob
Finch
Anthony
Towns
2013
Bdale Garbee and Keith Packard
This document is released under the terms of the
Creative Commons ShareAlike 3.0
license.
1.1.1
16 September 2012
Updated for software version 1.1.1 Version 1.1.1 fixes a few
bugs found in version 1.1.
1.1
13 September 2012
Updated for software version 1.1. Version 1.1 has new
features but is otherwise compatible with version 1.0.
1.0
24 August 2011
Updated for software version 1.0. Note that 1.0 represents a
telemetry format change, meaning both ends of a link
(TeleMetrum/TeleMini and TeleDongle) must be updated or
communications will fail.
0.9
18 January 2011
Updated for software version 0.9. Note that 0.9 represents a
telemetry format change, meaning both ends of a link (TeleMetrum and
TeleDongle) must be updated or communications will fail.
0.8
24 November 2010
Updated for software version 0.8
Thanks to Bob Finch, W9YA, NAR 12965, TRA 12350 for writing "The
Mere-Mortals Quick Start/Usage Guide to the Altus Metrum Starter
Kit" which formed the basis of the original Getting Started chapter
in this manual. Bob was one of our first customers for a production
TeleMetrum, and his continued enthusiasm and contributions
are immensely gratifying and highly appreciated!
And thanks to Anthony (AJ) Towns for major contributions including
the AltosUI graphing and site map code and associated documentation.
Free software means that our customers and friends can become our
collaborators, and we certainly appreciate this level of
contribution!
Have fun using these products, and we hope to meet all of you
out on the rocket flight line somewhere.
Bdale Garbee, KB0G
NAR #87103, TRA #12201
Keith Packard, KD7SQG
NAR #88757, TRA #12200
Introduction and Overview
Welcome to the Altus Metrum community! Our circuits and software reflect
our passion for both hobby rocketry and Free Software. We hope their
capabilities and performance will delight you in every way, but by
releasing all of our hardware and software designs under open licenses,
we also hope to empower you to take as active a role in our collective
future as you wish!
The first device created for our community was TeleMetrum, a dual
deploy altimeter with fully integrated GPS and radio telemetry
as standard features, and a "companion interface" that will
support optional capabilities in the future.
Our second device was TeleMini, a dual deploy altimeter with
radio telemetry and radio direction finding. This device is only
13mm by 38mm (½ inch by 1½ inches) and can fit easily in an 18mm
air-frame.
Complementing TeleMetrum and TeleMini is TeleDongle, a USB to RF
interface for communicating with the altimeters. Combined with your
choice of antenna and
notebook computer, TeleDongle and our associated user interface software
form a complete ground station capable of logging and displaying in-flight
telemetry, aiding rocket recovery, then processing and archiving flight
data for analysis and review.
More products will be added to the Altus Metrum family over time, and
we currently envision that this will be a single, comprehensive manual
for the entire product family.
Getting Started
The first thing to do after you check the inventory of parts in your
"starter kit" is to charge the battery.
The TeleMetrum battery can be charged by plugging it into the
corresponding socket of the TeleMetrum and then using the USB A to
mini B
cable to plug the TeleMetrum into your computer's USB socket. The
TeleMetrum circuitry will charge the battery whenever it is plugged
in, because the TeleMetrum's on-off switch does NOT control the
charging circuitry.
When the GPS chip is initially searching for
satellites, TeleMetrum will consume more current than it can pull
from the USB port, so the battery must be attached in order to get
satellite lock. Once GPS is locked, the current consumption goes back
down enough to enable charging while
running. So it's a good idea to fully charge the battery as your
first item of business so there is no issue getting and maintaining
satellite lock. The yellow charge indicator led will go out when the
battery is nearly full and the charger goes to trickle charge. It
can take several hours to fully recharge a deeply discharged battery.
The TeleMini battery can be charged by disconnecting it from the
TeleMini board and plugging it into a standalone battery charger
such as the LipoCharger product included in TeleMini Starter Kits,
and connecting that via a USB cable to a laptop or other USB
power source.
The other active device in the starter kit is the TeleDongle USB to
RF interface. If you plug it in to your Mac or Linux computer it should
"just work", showing up as a serial port device. Windows systems need
driver information that is part of the AltOS download to know that the
existing USB modem driver will work. We therefore recommend installing
our software before plugging in TeleDongle if you are using a Windows
computer. If you are using Linux and are having problems, try moving
to a fresher kernel (2.6.33 or newer), as the USB serial driver had
ugly bugs in some earlier versions.
Next you should obtain and install the AltOS software. These include
the AltosUI ground station program, current firmware images for
TeleMetrum, TeleMini and TeleDongle, and a number of standalone
utilities that are rarely needed. Pre-built binary packages are
available for Linux, Microsoft Windows, and recent MacOSX versions.
Full source code and build instructions are also available.
The latest version may always be downloaded from
.
Handling Precautions
All Altus Metrum products are sophisticated electronic devices.
When handled gently and properly installed in an air-frame, they
will deliver impressive results. However, as with all electronic
devices, there are some precautions you must take.
The Lithium Polymer rechargeable batteries have an
extraordinary power density. This is great because we can fly with
much less battery mass than if we used alkaline batteries or previous
generation rechargeable batteries... but if they are punctured
or their leads are allowed to short, they can and will release their
energy very rapidly!
Thus we recommend that you take some care when handling our batteries
and consider giving them some extra protection in your air-frame. We
often wrap them in suitable scraps of closed-cell packing foam before
strapping them down, for example.
The barometric sensors used on both TeleMetrum and TeleMini are
sensitive to sunlight. In normal TeleMetrum mounting situations, it
and all of the other surface mount components
are "down" towards whatever the underlying mounting surface is, so
this is not normally a problem. Please consider this, though, when
designing an installation, for example, in an air-frame with a
see-through plastic payload bay. It is particularly important to
consider this with TeleMini, both because the baro sensor is on the
"top" of the board, and because many model rockets with payload bays
use clear plastic for the payload bay! Replacing these with an opaque
cardboard tube, painting them, or wrapping them with a layer of masking
tape are all reasonable approaches to keep the sensor out of direct
sunlight.
The barometric sensor sampling port must be able to "breathe",
both by not being covered by foam or tape or other materials that might
directly block the hole on the top of the sensor, and also by having a
suitable static vent to outside air.
As with all other rocketry electronics, Altus Metrum altimeters must
be protected from exposure to corrosive motor exhaust and ejection
charge gasses.
Hardware Overview
TeleMetrum is a 1 inch by 2.75 inch circuit board. It was designed to
fit inside coupler for 29mm air-frame tubing, but using it in a tube that
small in diameter may require some creativity in mounting and wiring
to succeed! The presence of an accelerometer means TeleMetrum should
be aligned along the flight axis of the airframe, and by default the 1/4
wave UHF wire antenna should be on the nose-cone end of the board. The
antenna wire is about 7 inches long, and wiring for a power switch and
the e-matches for apogee and main ejection charges depart from the
fin can end of the board, meaning an ideal "simple" avionics
bay for TeleMetrum should have at least 10 inches of interior length.
TeleMini is a 0.5 inch by 1.5 inch circuit board. It was designed to
fit inside an 18mm air-frame tube, but using it in a tube that
small in diameter may require some creativity in mounting and wiring
to succeed! Since there is no accelerometer, TeleMini can be mounted
in any convenient orientation. The default 1/4
wave UHF wire antenna attached to the center of one end of
the board is about 7 inches long, and wiring for a power switch and
the e-matches for apogee and main ejection charges depart from the
other end of the board, meaning an ideal "simple" avionics
bay for TeleMini should have at least 9 inches of interior length.
A typical TeleMetrum or TeleMini installation involves attaching
only a suitable Lithium Polymer battery, a single pole switch for
power on/off, and two pairs of wires connecting e-matches for the
apogee and main ejection charges. All Altus Metrum products are
designed for use with single-cell batteries with 3.7 volts nominal.
The battery connectors are a standard 2-pin JST connector and
match batteries sold by Spark Fun. These batteries are
single-cell Lithium Polymer batteries that nominally provide 3.7
volts. Other vendors sell similar batteries for RC aircraft
using mating connectors, however the polarity for those is
generally reversed from the batteries used by Altus Metrum
products. In particular, the Tenergy batteries supplied for use
in Featherweight flight computers are not compatible with Altus
Metrum flight computers or battery chargers. Check
polarity and voltage before connecting any battery not purchased
from Altus Metrum or Spark Fun.
By default, we use the unregulated output of the Li-Po battery directly
to fire ejection charges. This works marvelously with standard
low-current e-matches like the J-Tek from MJG Technologies, and with
Quest Q2G2 igniters. However, if you want or need to use a separate
pyro battery, check out the "External Pyro Battery" section in this
manual for instructions on how to wire that up. The altimeters are
designed to work with an external pyro battery of no more than 15 volts.
Ejection charges are wired directly to the screw terminal block
at the aft end of the altimeter. You'll need a very small straight
blade screwdriver for these screws, such as you might find in a
jeweler's screwdriver set.
TeleMetrum also uses the screw terminal block for the power
switch leads. On TeleMini, the power switch leads are soldered
directly to the board and can be connected directly to a switch.
For most air-frames, the integrated antennas are more than
adequate. However, if you are installing in a carbon-fiber or
metal electronics bay which is opaque to RF signals, you may need to
use off-board external antennas instead. In this case, you can
order an altimeter with an SMA connector for the UHF antenna
connection, and, on TeleMetrum, you can unplug the integrated GPS
antenna and select an appropriate off-board GPS antenna with
cable terminating in a U.FL connector.
System Operation
Firmware Modes
The AltOS firmware build for the altimeters has two
fundamental modes, "idle" and "flight". Which of these modes
the firmware operates in is determined at start up time. For
TeleMetrum, the mode is controlled by the orientation of the
rocket (well, actually the board, of course...) at the time
power is switched on. If the rocket is "nose up", then
TeleMetrum assumes it's on a rail or rod being prepared for
launch, so the firmware chooses flight mode. However, if the
rocket is more or less horizontal, the firmware instead enters
idle mode. Since TeleMini doesn't have an accelerometer we can
use to determine orientation, "idle" mode is selected when the
board receives a command packet within the first five seconds
of operation; if no packet is received, the board enters
"flight" mode.
At power on, you will hear three beeps or see three flashes
("S" in Morse code for start up) and then a pause while
the altimeter completes initialization and self test, and decides
which mode to enter next.
In flight or "pad" mode, the altimeter engages the flight
state machine, goes into transmit-only mode to
send telemetry, and waits for launch to be detected.
Flight mode is indicated by an "di-dah-dah-dit" ("P" for pad)
on the beeper or lights, followed by beeps or flashes
indicating the state of the pyrotechnic igniter continuity.
One beep/flash indicates apogee continuity, two beeps/flashes
indicate main continuity, three beeps/flashes indicate both
apogee and main continuity, and one longer "brap" sound or
rapidly alternating lights indicates no continuity. For a
dual deploy flight, make sure you're getting three beeps or
flashes before launching! For apogee-only or motor eject
flights, do what makes sense.
If idle mode is entered, you will hear an audible "di-dit" or see
two short flashes ("I" for idle), and the flight state machine is
disengaged, thus no ejection charges will fire. The altimeters also
listen for the radio link when in idle mode for requests sent via
TeleDongle. Commands can be issued to a TeleMetrum in idle mode
over either
USB or the radio link equivalently. TeleMini only has the radio link.
Idle mode is useful for configuring the altimeter, for extracting data
from the on-board storage chip after flight, and for ground testing
pyro charges.
One "neat trick" of particular value when TeleMetrum is used with
very large air-frames, is that you can power the board up while the
rocket is horizontal, such that it comes up in idle mode. Then you can
raise the air-frame to launch position, and issue a 'reset' command
via TeleDongle over the radio link to cause the altimeter to reboot and
come up in flight mode. This is much safer than standing on the top
step of a rickety step-ladder or hanging off the side of a launch
tower with a screw-driver trying to turn on your avionics before
installing igniters!
GPS
TeleMetrum includes a complete GPS receiver. A complete explanation
of how GPS works is beyond the scope of this manual, but the bottom
line is that the TeleMetrum GPS receiver needs to lock onto at least
four satellites to obtain a solid 3 dimensional position fix and know
what time it is.
TeleMetrum provides backup power to the GPS chip any time a
battery is connected. This allows the receiver to "warm start" on
the launch rail much faster than if every power-on were a GPS
"cold start". In typical operations, powering up TeleMetrum
on the flight line in idle mode while performing final air-frame
preparation will be sufficient to allow the GPS receiver to cold
start and acquire lock. Then the board can be powered down during
RSO review and installation on a launch rod or rail. When the board
is turned back on, the GPS system should lock very quickly, typically
long before igniter installation and return to the flight line are
complete.
Controlling An Altimeter Over The Radio Link
One of the unique features of the Altus Metrum system is
the ability to create a two way command link between TeleDongle
and an altimeter using the digital radio transceivers built into
each device. This allows you to interact with the altimeter from
afar, as if it were directly connected to the computer.
Any operation which can be performed with TeleMetrum can
either be done with TeleMetrum directly connected to the
computer via the USB cable, or through the radio
link. TeleMini doesn't provide a USB connector and so it is
always communicated with over radio. Select the appropriate
TeleDongle device when the list of devices is presented and
AltosUI will interact with an altimeter over the radio link.
One oddity in the current interface is how AltosUI selects the
frequency for radio communications. Instead of providing
an interface to specifically configure the frequency, it uses
whatever frequency was most recently selected for the target
TeleDongle device in Monitor Flight mode. If you haven't ever
used that mode with the TeleDongle in question, select the
Monitor Flight button from the top level UI, and pick the
appropriate TeleDongle device. Once the flight monitoring
window is open, select the desired frequency and then close it
down again. All radio communications will now use that frequency.
Save Flight Data—Recover flight data from the rocket without
opening it up.
Configure altimeter apogee delays or main deploy heights
to respond to changing launch conditions. You can also
'reboot' the altimeter. Use this to remotely enable the
flight computer by turning TeleMetrum on in "idle" mode,
then once the air-frame is oriented for launch, you can
reboot the altimeter and have it restart in pad mode
without having to climb the scary ladder.
Fire Igniters—Test your deployment charges without snaking
wires out through holes in the air-frame. Simply assembly the
rocket as if for flight with the apogee and main charges
loaded, then remotely command the altimeter to fire the
igniters.
Operation over the radio link for configuring an altimeter, ground
testing igniters, and so forth uses the same RF frequencies as flight
telemetry. To configure the desired TeleDongle frequency, select
the monitor flight tab, then use the frequency selector and
close the window before performing other desired radio operations.
TeleMetrum only enables radio commanding in 'idle' mode, so
make sure you have TeleMetrum lying horizontally when you turn
it on. Otherwise, TeleMetrum will start in 'pad' mode ready for
flight, and will not be listening for command packets from TeleDongle.
TeleMini listens for a command packet for five seconds after
first being turned on, if it doesn't hear anything, it enters
'pad' mode, ready for flight and will no longer listen for
command packets. The easiest way to connect to TeleMini is to
initiate the command and select the TeleDongle device. At this
point, the TeleDongle will be attempting to communicate with
the TeleMini. Now turn TeleMini on, and it should immediately
start communicating with the TeleDongle and the desired
operation can be performed.
You can monitor the operation of the radio link by watching the
lights on the devices. The red LED will flash each time a packet
is transmitted, while the green LED will light up on TeleDongle when
it is waiting to receive a packet from the altimeter.
Ground Testing
An important aspect of preparing a rocket using electronic deployment
for flight is ground testing the recovery system. Thanks
to the bi-directional radio link central to the Altus Metrum system,
this can be accomplished in a TeleMetrum or TeleMini equipped rocket
with less work than you may be accustomed to with other systems. It
can even be fun!
Just prep the rocket for flight, then power up the altimeter
in "idle" mode (placing air-frame horizontal for TeleMetrum or
selected the Configure Altimeter tab for TeleMini). This will cause
the firmware to go into "idle" mode, in which the normal flight
state machine is disabled and charges will not fire without
manual command. You can now command the altimeter to fire the apogee
or main charges from a safe distance using your computer and
TeleDongle and the Fire Igniter tab to complete ejection testing.
Radio Link
The chip our boards are based on incorporates an RF transceiver, but
it's not a full duplex system... each end can only be transmitting or
receiving at any given moment. So we had to decide how to manage the
link.
By design, the altimeter firmware listens for the radio link when
it's in "idle mode", which
allows us to use the radio link to configure the rocket, do things like
ejection tests, and extract data after a flight without having to
crack open the air-frame. However, when the board is in "flight
mode", the altimeter only
transmits and doesn't listen at all. That's because we want to put
ultimate priority on event detection and getting telemetry out of
the rocket through
the radio in case the rocket crashes and we aren't able to extract
data later...
We don't use a 'normal packet radio' mode like APRS because they're
just too inefficient. The GFSK modulation we use is FSK with the
base-band pulses passed through a
Gaussian filter before they go into the modulator to limit the
transmitted bandwidth. When combined with the hardware forward error
correction support in the cc1111 chip, this allows us to have a very
robust 38.4 kilobit data link with only 10 milliwatts of transmit
power, a whip antenna in the rocket, and a hand-held Yagi on the
ground. We've had flights to above 21k feet AGL with great reception,
and calculations suggest we should be good to well over 40k feet AGL
with a 5-element yagi on the ground. We hope to fly boards to higher
altitudes over time, and would of course appreciate customer feedback
on performance in higher altitude flights!
Configurable Parameters
Configuring an Altus Metrum altimeter for flight is very
simple. Even on our baro-only TeleMini board, the use of a Kalman
filter means there is no need to set a "mach delay". The few
configurable parameters can all be set using AltosUI over USB or
or radio link via TeleDongle.
Radio Frequency
Altus Metrum boards support radio frequencies in the 70cm
band. By default, the configuration interface provides a
list of 10 "standard" frequencies in 100kHz channels starting at
434.550MHz. However, the firmware supports use of
any 50kHz multiple within the 70cm band. At any given
launch, we highly recommend coordinating when and by whom each
frequency will be used to avoid interference. And of course, both
altimeter and TeleDongle must be configured to the same
frequency to successfully communicate with each other.
Apogee Delay
Apogee delay is the number of seconds after the altimeter detects flight
apogee that the drogue charge should be fired. In most cases, this
should be left at the default of 0. However, if you are flying
redundant electronics such as for an L3 certification, you may wish
to set one of your altimeters to a positive delay so that both
primary and backup pyrotechnic charges do not fire simultaneously.
The Altus Metrum apogee detection algorithm fires exactly at
apogee. If you are also flying an altimeter like the
PerfectFlite MAWD, which only supports selecting 0 or 1
seconds of apogee delay, you may wish to set the MAWD to 0
seconds delay and set the TeleMetrum to fire your backup 2
or 3 seconds later to avoid any chance of both charges
firing simultaneously. We've flown several air-frames this
way quite happily, including Keith's successful L3 cert.
Main Deployment Altitude
By default, the altimeter will fire the main deployment charge at an
elevation of 250 meters (about 820 feet) above ground. We think this
is a good elevation for most air-frames, but feel free to change this
to suit. In particular, if you are flying two altimeters, you may
wish to set the
deployment elevation for the backup altimeter to be something lower
than the primary so that both pyrotechnic charges don't fire
simultaneously.
Maximum Flight Log
TeleMetrum version 1.1 and 1.2 have 2MB of on-board flash storage,
enough to hold over 40 minutes of data at full data rate
(100 samples/second). TeleMetrum 1.0 has 1MB of on-board
storage. As data are stored at a reduced rate during descent
(10 samples/second), there's plenty of space to store many
flights worth of data.
The on-board flash is partitioned into separate flight logs,
each of a fixed maximum size. Increase the maximum size of
each log and you reduce the number of flights that can be
stored. Decrease the size and TeleMetrum can store more
flights.
All of the configuration data is also stored in the flash
memory, which consumes 64kB on TeleMetrum v1.1/v1.2 and 256B on
TeleMetrum v1.0. This configuration space is not available
for storing flight log data.
To compute the amount of space needed for a single flight,
you can multiply the expected ascent time (in seconds) by
800, multiply the expected descent time (in seconds) by 80
and add the two together. That will slightly under-estimate
the storage (in bytes) needed for the flight. For instance,
a flight spending 20 seconds in ascent and 150 seconds in
descent will take about (20 * 800) + (150 * 80) = 28000
bytes of storage. You could store dozens of these flights in
the on-board flash.
The default size, 192kB, allows for 10 flights of storage on
TeleMetrum v1.1/v1.2 and 5 flights on TeleMetrum v1.0. This
ensures that you won't need to erase the memory before
flying each time while still allowing more than sufficient
storage for each flight.
As TeleMini does not contain an accelerometer, it stores
data at 10 samples per second during ascent and one sample
per second during descent. Each sample is a two byte reading
from the barometer. These are stored in 5kB of
on-chip flash memory which can hold 256 seconds at the
ascent rate or 2560 seconds at the descent rate. Because of
the limited storage, TeleMini cannot hold data for more than
one flight, and so must be erased after each flight or it
will not capture data for subsequent flights.
Ignite Mode
Instead of firing one charge at apogee and another charge at
a fixed height above the ground, you can configure the
altimeter to fire both at apogee or both during
descent. This was added to support an airframe that has two
TeleMetrum computers, one in the fin can and one in the
nose.
Providing the ability to use both igniters for apogee or
main allows some level of redundancy without needing two
flight computers. In Redundant Apogee or Redundant Main
mode, the two charges will be fired two seconds apart.
Pad Orientation
TeleMetrum measures acceleration along the axis of the
board. Which way the board is oriented affects the sign of
the acceleration value. Instead of trying to guess which way
the board is mounted in the air frame, TeleMetrum must be
explicitly configured for either Antenna Up or Antenna
Down. The default, Antenna Up, expects the end of the
TeleMetrum board connected to the 70cm antenna to be nearest
the nose of the rocket, with the end containing the screw
terminals nearest the tail.
AltosUI
The AltosUI program provides a graphical user interface for
interacting with the Altus Metrum product family, including
TeleMetrum, TeleMini and TeleDongle. AltosUI can monitor telemetry data,
configure TeleMetrum, TeleMini and TeleDongle devices and many other
tasks. The primary interface window provides a selection of
buttons, one for each major activity in the system. This manual
is split into chapters, each of which documents one of the tasks
provided from the top-level toolbar.
Monitor Flight
Receive, Record and Display Telemetry Data
Selecting this item brings up a dialog box listing all of the
connected TeleDongle devices. When you choose one of these,
AltosUI will create a window to display telemetry data as
received by the selected TeleDongle device.
All telemetry data received are automatically recorded in
suitable log files. The name of the files includes the current
date and rocket serial and flight numbers.
The radio frequency being monitored by the TeleDongle device is
displayed at the top of the window. You can configure the
frequency by clicking on the frequency box and selecting the desired
frequency. AltosUI remembers the last frequency selected for each
TeleDongle and selects that automatically the next time you use
that device.
Below the TeleDongle frequency selector, the window contains a few
significant pieces of information about the altimeter providing
the telemetry data stream:
The configured call-sign
The device serial number
The flight number. Each altimeter remembers how many
times it has flown.
The rocket flight state. Each flight passes through several
states including Pad, Boost, Fast, Coast, Drogue, Main and
Landed.
The Received Signal Strength Indicator value. This lets
you know how strong a signal TeleDongle is receiving. The
radio inside TeleDongle operates down to about -99dBm;
weaker signals may not be receivable. The packet link uses
error detection and correction techniques which prevent
incorrect data from being reported.
The age of the displayed data, in seconds since the last
successfully received telemetry packet. In normal operation
this will stay in the low single digits. If the number starts
counting up, then you are no longer receiving data over the radio
link from the flight computer.
Finally, the largest portion of the window contains a set of
tabs, each of which contain some information about the rocket.
They're arranged in 'flight order' so that as the flight
progresses, the selected tab automatically switches to display
data relevant to the current state of the flight. You can select
other tabs at any time. The final 'table' tab displays all of
the raw telemetry values in one place in a spreadsheet-like format.
Launch Pad
The 'Launch Pad' tab shows information used to decide when the
rocket is ready for flight. The first elements include red/green
indicators, if any of these is red, you'll want to evaluate
whether the rocket is ready to launch:
Battery Voltage. This indicates whether the Li-Po battery
powering the TeleMetrum has sufficient charge to last for
the duration of the flight. A value of more than
3.7V is required for a 'GO' status.
Apogee Igniter Voltage. This indicates whether the apogee
igniter has continuity. If the igniter has a low
resistance, then the voltage measured here will be close
to the Li-Po battery voltage. A value greater than 3.2V is
required for a 'GO' status.
Main Igniter Voltage. This indicates whether the main
igniter has continuity. If the igniter has a low
resistance, then the voltage measured here will be close
to the Li-Po battery voltage. A value greater than 3.2V is
required for a 'GO' status.
On-board Data Logging. This indicates whether there is
space remaining on-board to store flight data for the
upcoming flight. If you've downloaded data, but failed
to erase flights, there may not be any space
left. TeleMetrum can store multiple flights, depending
on the configured maximum flight log size. TeleMini
stores only a single flight, so it will need to be
downloaded and erased after each flight to capture
data. This only affects on-board flight logging; the
altimeter will still transmit telemetry and fire
ejection charges at the proper times.
GPS Locked. For a TeleMetrum device, this indicates whether the GPS receiver is
currently able to compute position information. GPS requires
at least 4 satellites to compute an accurate position.
GPS Ready. For a TeleMetrum device, this indicates whether GPS has reported at least
10 consecutive positions without losing lock. This ensures
that the GPS receiver has reliable reception from the
satellites.
The Launchpad tab also shows the computed launch pad position
and altitude, averaging many reported positions to improve the
accuracy of the fix.
Ascent
This tab is shown during Boost, Fast and Coast
phases. The information displayed here helps monitor the
rocket as it heads towards apogee.
The height, speed and acceleration are shown along with the
maximum values for each of them. This allows you to quickly
answer the most commonly asked questions you'll hear during
flight.
The current latitude and longitude reported by the TeleMetrum GPS are
also shown. Note that under high acceleration, these values
may not get updated as the GPS receiver loses position
fix. Once the rocket starts coasting, the receiver should
start reporting position again.
Finally, the current igniter voltages are reported as in the
Launch Pad tab. This can help diagnose deployment failures
caused by wiring which comes loose under high acceleration.
Descent
Once the rocket has reached apogee and (we hope) activated the
apogee charge, attention switches to tracking the rocket on
the way back to the ground, and for dual-deploy flights,
waiting for the main charge to fire.
To monitor whether the apogee charge operated correctly, the
current descent rate is reported along with the current
height. Good descent rates vary based on the choice of recovery
components, but generally range from 15-30m/s on drogue and should
be below 10m/s when under the main parachute in a dual-deploy flight.
For TeleMetrum altimeters, you can locate the rocket in the
sky using the elevation and bearing information to figure
out where to look. Elevation is in degrees above the
horizon. Bearing is reported in degrees relative to true
north. Range can help figure out how big the rocket will
appear. Ground Distance shows how far it is to a point
directly under the rocket and can help figure out where the
rocket is likely to land. Note that all of these values are
relative to the pad location. If the elevation is near 90°,
the rocket is over the pad, not over you.
Finally, the igniter voltages are reported in this tab as
well, both to monitor the main charge as well as to see what
the status of the apogee charge is. Note that some commercial
e-matches are designed to retain continuity even after being
fired, and will continue to show as green or return from red to
green after firing.
Landed
Once the rocket is on the ground, attention switches to
recovery. While the radio signal is often lost once the
rocket is on the ground, the last reported GPS position is
generally within a short distance of the actual landing location.
The last reported GPS position is reported both by
latitude and longitude as well as a bearing and distance from
the launch pad. The distance should give you a good idea of
whether to walk or hitch a ride. Take the reported
latitude and longitude and enter them into your hand-held GPS
unit and have that compute a track to the landing location.
Both TeleMini and TeleMetrum will continue to transmit RDF
tones after landing, allowing you to locate the rocket by
following the radio signal if necessary. You may need to get
away from the clutter of the flight line, or even get up on
a hill (or your neighbor's RV roof) to receive the RDF signal.
The maximum height, speed and acceleration reported
during the flight are displayed for your admiring observers.
The accuracy of these immediate values depends on the quality
of your radio link and how many packets were received.
Recovering the on-board data after flight will likely yield
more precise results.
To get more detailed information about the flight, you can
click on the 'Graph Flight' button which will bring up a
graph window for the current flight.
Site Map
When the TeleMetrum has a GPS fix, the Site Map tab will map
the rocket's position to make it easier for you to locate the
rocket, both while it is in the air, and when it has landed. The
rocket's state is indicated by color: white for pad, red for
boost, pink for fast, yellow for coast, light blue for drogue,
dark blue for main, and black for landed.
The map's scale is approximately 3m (10ft) per pixel. The map
can be dragged using the left mouse button. The map will attempt
to keep the rocket roughly centered while data is being received.
Images are fetched automatically via the Google Maps Static API,
and cached on disk for reuse. If map images cannot be downloaded,
the rocket's path will be traced on a dark gray background
instead.
You can pre-load images for your favorite launch sites
before you leave home; check out the 'Preload Maps' section below.
Save Flight Data
The altimeter records flight data to its internal flash memory.
TeleMetrum data is recorded at a much higher rate than the telemetry
system can handle, and is not subject to radio drop-outs. As
such, it provides a more complete and precise record of the
flight. The 'Save Flight Data' button allows you to read the
flash memory and write it to disk. As TeleMini has only a barometer, it
records data at the same rate as the telemetry signal, but there will be
no data lost due to telemetry drop-outs.
Clicking on the 'Save Flight Data' button brings up a list of
connected TeleMetrum and TeleDongle devices. If you select a
TeleMetrum device, the flight data will be downloaded from that
device directly. If you select a TeleDongle device, flight data
will be downloaded from an altimeter over radio link via the
specified TeleDongle. See the chapter on Controlling An Altimeter
Over The Radio Link for more information.
After the device has been selected, a dialog showing the
flight data saved in the device will be shown allowing you to
select which flights to download and which to delete. With
version 0.9 or newer firmware, you must erase flights in order
for the space they consume to be reused by another
flight. This prevents accidentally losing flight data
if you neglect to download data before flying again. Note that
if there is no more space available in the device, then no
data will be recorded during the next flight.
The file name for each flight log is computed automatically
from the recorded flight date, altimeter serial number and
flight number information.
Replay Flight
Select this button and you are prompted to select a flight
record file, either a .telem file recording telemetry data or a
.eeprom file containing flight data saved from the altimeter
flash memory.
Once a flight record is selected, the flight monitor interface
is displayed and the flight is re-enacted in real time. Check
the Monitor Flight chapter above to learn how this window operates.
Graph Data
Select this button and you are prompted to select a flight
record file, either a .telem file recording telemetry data or a
.eeprom file containing flight data saved from
flash memory.
Once a flight record is selected, a window with two tabs is
opened. The first tab contains a graph with acceleration
(blue), velocity (green) and altitude (red) of the flight,
measured in metric units. The
apogee(yellow) and main(magenta) igniter voltages are also
displayed; high voltages indicate continuity, low voltages
indicate open circuits. The second tab contains some basic
flight statistics.
The graph can be zoomed into a particular area by clicking and
dragging down and to the right. Once zoomed, the graph can be
reset by clicking and dragging up and to the left. Holding down
control and clicking and dragging allows the graph to be panned.
The right mouse button causes a pop-up menu to be displayed, giving
you the option save or print the plot.
Note that telemetry files will generally produce poor graphs
due to the lower sampling rate and missed telemetry packets.
Use saved flight data in .eeprom files for graphing where possible.
Export Data
This tool takes the raw data files and makes them available for
external analysis. When you select this button, you are prompted to
select a flight
data file (either .eeprom or .telem will do, remember that
.eeprom files contain higher resolution and more continuous
data). Next, a second dialog appears which is used to select
where to write the resulting file. It has a selector to choose
between CSV and KML file formats.
Comma Separated Value Format
This is a text file containing the data in a form suitable for
import into a spreadsheet or other external data analysis
tool. The first few lines of the file contain the version and
configuration information from the altimeter, then
there is a single header line which labels all of the
fields. All of these lines start with a '#' character which
many tools can be configured to skip over.
The remaining lines of the file contain the data, with each
field separated by a comma and at least one space. All of
the sensor values are converted to standard units, with the
barometric data reported in both pressure, altitude and
height above pad units.
Keyhole Markup Language (for Google Earth)
This is the format used by Google Earth to provide an overlay
within that application. With this, you can use Google Earth to
see the whole flight path in 3D.
Configure Altimeter
Select this button and then select either a TeleMetrum or
TeleDongle Device from the list provided. Selecting a TeleDongle
device will use the radio link to configure a remote altimeter.
The first few lines of the dialog provide information about the
connected device, including the product name,
software version and hardware serial number. Below that are the
individual configuration entries.
At the bottom of the dialog, there are four buttons:
Save. This writes any changes to the
configuration parameter block in flash memory. If you don't
press this button, any changes you make will be lost.
Reset. This resets the dialog to the most recently saved values,
erasing any changes you have made.
Reboot. This reboots the device. Use this to
switch from idle to pad mode by rebooting once the rocket is
oriented for flight, or to confirm changes you think you saved
are really saved.
Close. This closes the dialog. Any unsaved changes will be
lost.
The rest of the dialog contains the parameters to be configured.
Main Deploy Altitude
This sets the altitude (above the recorded pad altitude) at
which the 'main' igniter will fire. The drop-down menu shows
some common values, but you can edit the text directly and
choose whatever you like. If the apogee charge fires below
this altitude, then the main charge will fire two seconds
after the apogee charge fires.
Apogee Delay
When flying redundant electronics, it's often important to
ensure that multiple apogee charges don't fire at precisely
the same time, as that can over pressurize the apogee deployment
bay and cause a structural failure of the air-frame. The Apogee
Delay parameter tells the flight computer to fire the apogee
charge a certain number of seconds after apogee has been
detected.
Radio Frequency
This configures which of the configured frequencies to use for both
telemetry and packet command mode. Note that if you set this
value via packet command mode, you will have to reconfigure
the TeleDongle frequency before you will be able to use packet
command mode again.
Radio Calibration
The radios in every Altus Metrum device are calibrated at the
factory to ensure that they transmit and receive on the
specified frequency. If you need to you can adjust the calibration
by changing this value. Do not do this without understanding what
the value means, read the appendix on calibration and/or the source
code for more information. To change a TeleDongle's calibration,
you must reprogram the unit completely.
Callsign
This sets the call sign included in each telemetry packet. Set this
as needed to conform to your local radio regulations.
Maximum Flight Log Size
This sets the space (in kilobytes) allocated for each flight
log. The available space will be divided into chunks of this
size. A smaller value will allow more flights to be stored,
a larger value will record data from longer flights.
Ignite Mode
TeleMetrum and TeleMini provide two igniter channels as they
were originally designed as dual-deploy flight
computers. This configuration parameter allows the two
channels to be used in different configurations.
Dual Deploy. This is the usual mode of operation; the
'apogee' channel is fired at apogee and the 'main'
channel at the height above ground specified by the
'Main Deploy Altitude' during descent.
Redundant Apogee. This fires both channels at
apogee, the 'apogee' channel first followed after a two second
delay by the 'main' channel.
Redundant Main. This fires both channels at the
height above ground specified by the Main Deploy
Altitude setting during descent. The 'apogee'
channel is fired first, followed after a two second
delay by the 'main' channel.
Pad Orientation
Because it includes an accelerometer, TeleMetrum is
sensitive to the orientation of the board. By default, it
expects the antenna end to point forward. This parameter
allows that default to be changed, permitting the board to
be mounted with the antenna pointing aft instead.
Antenna Up. In this mode, the antenna end of the
TeleMetrum board must point forward, in line with the
expected flight path.
Antenna Down. In this mode, the antenna end of the
TeleMetrum board must point aft, in line with the
expected flight path.
Configure AltosUI
This button presents a dialog so that you can configure the AltosUI global settings.
Voice Settings
AltosUI provides voice announcements during flight so that you
can keep your eyes on the sky and still get information about
the current flight status. However, sometimes you don't want
to hear them.
Enable—turns all voice announcements on and off
Test Voice—Plays a short message allowing you to verify
that the audio system is working and the volume settings
are reasonable
Log Directory
AltosUI logs all telemetry data and saves all TeleMetrum flash
data to this directory. This directory is also used as the
staring point when selecting data files for display or export.
Click on the directory name to bring up a directory choosing
dialog, select a new directory and click 'Select Directory' to
change where AltosUI reads and writes data files.
Callsign
This value is transmitted in each command packet sent from
TeleDongle and received from an altimeter. It is not used in
telemetry mode, as the callsign configured in the altimeter board
is included in all telemetry packets. Configure this
with the AltosUI operators call sign as needed to comply with
your local radio regulations.
Imperial Units
This switches between metric units (meters) and imperial
units (feet and miles). This affects the display of values
use during flight monitoring, data graphing and all of the
voice announcements. It does not change the units used when
exporting to CSV files, those are always produced in metric units.
Font Size
Selects the set of fonts used in the flight monitor
window. Choose between the small, medium and large sets.
Serial Debug
This causes all communication with a connected device to be
dumped to the console from which AltosUI was started. If
you've started it from an icon or menu entry, the output
will simply be discarded. This mode can be useful to debug
various serial communication issues.
Manage Frequencies
This brings up a dialog where you can configure the set of
frequencies shown in the various frequency menus. You can
add as many as you like, or even reconfigure the default
set. Changing this list does not affect the frequency
settings of any devices, it only changes the set of
frequencies shown in the menus.
Configure Groundstation
Select this button and then select a TeleDongle Device from the list provided.
The first few lines of the dialog provide information about the
connected device, including the product name,
software version and hardware serial number. Below that are the
individual configuration entries.
Note that the TeleDongle itself doesn't save any configuration
data, the settings here are recorded on the local machine in
the Java preferences database. Moving the TeleDongle to
another machine, or using a different user account on the same
machine will cause settings made here to have no effect.
At the bottom of the dialog, there are three buttons:
Save. This writes any changes to the
local Java preferences file. If you don't
press this button, any changes you make will be lost.
Reset. This resets the dialog to the most recently saved values,
erasing any changes you have made.
Close. This closes the dialog. Any unsaved changes will be
lost.
The rest of the dialog contains the parameters to be configured.
Frequency
This configures the frequency to use for both telemetry and
packet command mode. Set this before starting any operation
involving packet command mode so that it will use the right
frequency. Telemetry monitoring mode also provides a menu to
change the frequency, and that menu also sets the same Java
preference value used here.
Radio Calibration
The radios in every Altus Metrum device are calibrated at the
factory to ensure that they transmit and receive on the
specified frequency. To change a TeleDongle's calibration,
you must reprogram the unit completely, so this entry simply
shows the current value and doesn't allow any changes.
Flash Image
This reprograms any Altus Metrum device by using a TeleMetrum
or TeleDongle as a programming dongle. Please read the
directions for flashing devices in the Updating Device
Firmware chapter below.
Once you have the programmer and target devices connected,
push the 'Flash Image' button. That will present a dialog box
listing all of the connected devices. Carefully select the
programmer device, not the device to be programmed.
Next, select the image to flash to the device. These are named
with the product name and firmware version. The file selector
will start in the directory containing the firmware included
with the AltosUI package. Navigate to the directory containing
the desired firmware if it isn't there.
Next, a small dialog containing the device serial number and
RF calibration values should appear. If these values are
incorrect (possibly due to a corrupted image in the device),
enter the correct values here.
Finally, a dialog containing a progress bar will follow the
programming process.
When programming is complete, the target device will
reboot. Note that if the target device is connected via USB, you
will have to unplug it and then plug it back in for the USB
connection to reset so that you can communicate with the device
again.
Fire Igniter
This activates the igniter circuits in TeleMetrum to help test
recovery systems deployment. Because this command can operate
over the Packet Command Link, you can prepare the rocket as
for flight and then test the recovery system without needing
to snake wires inside the air-frame.
Selecting the 'Fire Igniter' button brings up the usual device
selection dialog. Pick the desired TeleDongle or TeleMetrum
device. This brings up another window which shows the current
continuity test status for both apogee and main charges.
Next, select the desired igniter to fire. This will enable the
'Arm' button.
Select the 'Arm' button. This enables the 'Fire' button. The
word 'Arm' is replaced by a countdown timer indicating that
you have 10 seconds to press the 'Fire' button or the system
will deactivate, at which point you start over again at
selecting the desired igniter.
Scan Channels
This listens for telemetry packets on all of the configured
frequencies, displaying information about each device it
receives a packet from. You can select which of the three
telemetry formats should be tried; by default, it only listens
for the standard telemetry packets used in v1.0 and later
firmware.
Load Maps
Before heading out to a new launch site, you can use this to
load satellite images in case you don't have internet
connectivity at the site. This loads a fairly large area
around the launch site, which should cover any flight you're likely to make.
There's a drop-down menu of launch sites we know about; if
your favorites aren't there, please let us know the lat/lon
and name of the site. The contents of this list are actually
downloaded at run-time, so as new sites are sent in, they'll
get automatically added to this list.
If the launch site isn't in the list, you can manually enter the lat/lon values
Clicking the 'Load Map' button will fetch images from Google
Maps; note that Google limits how many images you can fetch at
once, so if you load more than one launch site, you may get
some gray areas in the map which indicate that Google is tired
of sending data to you. Try again later.
Monitor Idle
This brings up a dialog similar to the Monitor Flight UI,
except it works with the altimeter in "idle" mode by sending
query commands to discover the current state rather than
listening for telemetry packets.
Using Altus Metrum Products
Being Legal
First off, in the US, you need an amateur radio license or
other authorization to legally operate the radio transmitters that are part
of our products.
In the Rocket
In the rocket itself, you just need a TeleMetrum or
TeleMini board and
a single-cell, 3.7 volt nominal Li-Po rechargeable battery. An
850mAh battery weighs less than a 9V alkaline battery, and will
run a TeleMetrum for hours.
A 110mAh battery weighs less than a triple A battery and will run a TeleMetrum for
a few hours, or a TeleMini for much (much) longer.
By default, we ship the altimeters with a simple wire antenna. If your
electronics bay or the air-frame it resides within is made of carbon fiber,
which is opaque to RF signals, you may choose to have an SMA connector
installed so that you can run a coaxial cable to an antenna mounted
elsewhere in the rocket.
On the Ground
To receive the data stream from the rocket, you need an antenna and short
feed-line connected to one of our TeleDongle units. If possible, use an SMA to BNC
adapter instead of feedline between the antenna feedpoint and
TeleDongle, as this will give you the best performance. The
TeleDongle in turn plugs directly into the USB port on a notebook
computer. Because TeleDongle looks like a simple serial port, your computer
does not require special device drivers... just plug it in.
The GUI tool, AltosUI, is written in Java and runs across
Linux, Mac OS and Windows. There's also a suite of C tools
for Linux which can perform most of the same tasks.
After the flight, you can use the radio link to extract the more detailed data
logged in either TeleMetrum or TeleMini devices, or you can use a mini USB cable to plug into the
TeleMetrum board directly. Pulling out the data without having to open up
the rocket is pretty cool! A USB cable is also how you charge the Li-Po
battery, so you'll want one of those anyway... the same cable used by lots
of digital cameras and other modern electronic stuff will work fine.
If your TeleMetrum-equipped rocket lands out of sight, you may enjoy having a hand-held GPS
receiver, so that you can put in a way-point for the last reported rocket
position before touch-down. This makes looking for your rocket a lot like
Geo-Caching... just go to the way-point and look around starting from there.
You may also enjoy having a ham radio "HT" that covers the 70cm band... you
can use that with your antenna to direction-find the rocket on the ground
the same way you can use a Walston or Beeline tracker. This can be handy
if the rocket is hiding in sage brush or a tree, or if the last GPS position
doesn't get you close enough because the rocket dropped into a canyon, or
the wind is blowing it across a dry lake bed, or something like that... Keith
and Bdale both currently own and use the Yaesu VX-7R at launches.
So, to recap, on the ground the hardware you'll need includes:
an antenna and feed-line or adapter
a TeleDongle
a notebook computer
optionally, a hand-held GPS receiver
optionally, an HT or receiver covering 435 MHz
The best hand-held commercial directional antennas we've found for radio
direction finding rockets are from
Arrow Antennas.
The 440-3 and 440-5 are both good choices for finding a
TeleMetrum- or TeleMini- equipped rocket when used with a suitable
70cm HT. TeleDongle and an SMA to BNC adapter fit perfectly
between the driven element and reflector of Arrow antennas.
Data Analysis
Our software makes it easy to log the data from each flight, both the
telemetry received during the flight itself, and the more
complete data log recorded in the flash memory on the altimeter
board. Once this data is on your computer, our post-flight tools make it
easy to quickly get to the numbers everyone wants, like apogee altitude,
max acceleration, and max velocity. You can also generate and view a
standard set of plots showing the altitude, acceleration, and
velocity of the rocket during flight. And you can even export a TeleMetrum data file
usable with Google Maps and Google Earth for visualizing the flight path
in two or three dimensions!
Our ultimate goal is to emit a set of files for each flight that can be
published as a web page per flight, or just viewed on your local disk with
a web browser.
Future Plans
In the future, we intend to offer "companion boards" for the rocket
that will plug in to TeleMetrum to collect additional data, provide
more pyro channels, and so forth.
Also under design is a new flight computer with more sensors, more
pyro channels, and a more powerful radio system designed for use
in multi-stage, complex, and extreme altitude projects.
We are also working on alternatives to TeleDongle. One is a
a stand-alone, hand-held ground terminal that will allow monitoring
the rocket's status, collecting data during flight, and logging data
after flight without the need for a notebook computer on the
flight line. Particularly since it is so difficult to read most
notebook screens in direct sunlight, we think this will be a great
thing to have. We are also working on a TeleDongle variant with
Bluetooth that will work with Android phones and tablets.
Because all of our work is open, both the hardware designs and the
software, if you have some great idea for an addition to the current
Altus Metrum family, feel free to dive in and help! Or let us know
what you'd like to see that we aren't already working on, and maybe
we'll get excited about it too...
Watch our
web site for more news
and information as our family of products evolves!
Altimeter Installation Recommendations
Building high-power rockets that fly safely is hard enough. Mix
in some sophisticated electronics and a bunch of radio energy
and oftentimes you find few perfect solutions. This chapter
contains some suggestions about how to install Altus Metrum
products into the rocket air-frame, including how to safely and
reliably mix a variety of electronics into the same air-frame.
Mounting the Altimeter
The first consideration is to ensure that the altimeter is
securely fastened to the air-frame. For TeleMetrum, we use
nylon standoffs and nylon screws; they're good to at least 50G
and cannot cause any electrical issues on the board. For
TeleMini, we usually cut small pieces of 1/16" balsa to fit
under the screw holes, and then take 2x56 nylon screws and
screw them through the TeleMini mounting holes, through the
balsa and into the underlying material.
Make sure TeleMetrum is aligned precisely along the axis of
acceleration so that the accelerometer can accurately
capture data during the flight.
Watch for any metal touching components on the
board. Shorting out connections on the bottom of the board
can cause the altimeter to fail during flight.
Dealing with the Antenna
The antenna supplied is just a piece of solid, insulated,
wire. If it gets damaged or broken, it can be easily
replaced. It should be kept straight and not cut; bending or
cutting it will change the resonant frequency and/or
impedance, making it a less efficient radiator and thus
reducing the range of the telemetry signal.
Keeping metal away from the antenna will provide better range
and a more even radiation pattern. In most rockets, it's not
entirely possible to isolate the antenna from metal
components; there are often bolts, all-thread and wires from other
electronics to contend with. Just be aware that the more stuff
like this around the antenna, the lower the range.
Make sure the antenna is not inside a tube made or covered
with conducting material. Carbon fiber is the most common
culprit here -- CF is a good conductor and will effectively
shield the antenna, dramatically reducing signal strength and
range. Metallic flake paint is another effective shielding
material which is to be avoided around any antennas.
If the ebay is large enough, it can be convenient to simply
mount the altimeter at one end and stretch the antenna out
inside. Taping the antenna to the sled can keep it straight
under acceleration. If there are metal rods, keep the
antenna as far away as possible.
For a shorter ebay, it's quite practical to have the antenna
run through a bulkhead and into an adjacent bay. Drill a small
hole in the bulkhead, pass the antenna wire through it and
then seal it up with glue or clay. We've also used acrylic
tubing to create a cavity for the antenna wire. This works a
bit better in that the antenna is known to stay straight and
not get folded by recovery components in the bay. Angle the
tubing towards the side wall of the rocket and it ends up
consuming very little space.
If you need to place the antenna at a distance from the
altimeter, you can replace the antenna with an edge-mounted
SMA connector, and then run 50Ω coax from the board to the
antenna. Building a remote antenna is beyond the scope of this
manual.
Preserving GPS Reception
The GPS antenna and receiver in TeleMetrum are highly
sensitive and normally have no trouble tracking enough
satellites to provide accurate position information for
recovering the rocket. However, there are many ways to
attenuate the GPS signal.
Conductive tubing or coatings. Carbon fiber and metal
tubing, or metallic paint will all dramatically attenuate the
GPS signal. We've never heard of anyone successfully
receiving GPS from inside these materials.
Metal components near the GPS patch antenna. These will
de-tune the patch antenna, changing the resonant frequency
away from the L1 carrier and reduce the effectiveness of the
antenna. You can place as much stuff as you like beneath the
antenna as that's covered with a ground plane. But, keep
wires and metal out from above the patch antenna.
Radio Frequency Interference
Any altimeter will generate RFI; the digital circuits use
high-frequency clocks that spray radio interference across a
wide band. Altus Metrum altimeters generate intentional radio
signals as well, increasing the amount of RF energy around the board.
Rocketry altimeters also use precise sensors measuring air
pressure and acceleration. Tiny changes in voltage can cause
these sensor readings to vary by a huge amount. When the
sensors start mis-reporting data, the altimeter can either
fire the igniters at the wrong time, or not fire them at all.
Voltages are induced when radio frequency energy is
transmitted from one circuit to another. Here are things that
influence the induced voltage and current:
Keep wires from different circuits apart. Moving circuits
further apart will reduce RFI.
Avoid parallel wires from different circuits. The longer two
wires run parallel to one another, the larger the amount of
transferred energy. Cross wires at right angles to reduce
RFI.
Twist wires from the same circuits. Two wires the same
distance from the transmitter will get the same amount of
induced energy which will then cancel out. Any time you have
a wire pair running together, twist the pair together to
even out distances and reduce RFI. For altimeters, this
includes battery leads, switch hookups and igniter
circuits.
Avoid resonant lengths. Know what frequencies are present
in the environment and avoid having wire lengths near a
natural resonant length. Altusmetrum products transmit on the
70cm amateur band, so you should avoid lengths that are a
simple ratio of that length; essentially any multiple of 1/4
of the wavelength (17.5cm).
The Barometric Sensor
Altusmetrum altimeters measure altitude with a barometric
sensor, essentially measuring the amount of air above the
rocket to figure out how high it is. A large number of
measurements are taken as the altimeter initializes itself to
figure out the pad altitude. Subsequent measurements are then
used to compute the height above the pad.
To accurately measure atmospheric pressure, the ebay
containing the altimeter must be vented outside the
air-frame. The vent must be placed in a region of linear
airflow, have smooth edges, and away from areas of increasing or
decreasing pressure.
The barometric sensor in the altimeter is quite sensitive to
chemical damage from the products of APCP or BP combustion, so
make sure the ebay is carefully sealed from any compartment
which contains ejection charges or motors.
Ground Testing
The most important aspect of any installation is careful
ground testing. Bringing an air-frame up to the LCO table which
hasn't been ground tested can lead to delays or ejection
charges firing on the pad, or, even worse, a recovery system
failure.
Do a 'full systems' test that includes wiring up all igniters
without any BP and turning on all of the electronics in flight
mode. This will catch any mistakes in wiring and any residual
RFI issues that might accidentally fire igniters at the wrong
time. Let the air-frame sit for several minutes, checking for
adequate telemetry signal strength and GPS lock. If any igniters
fire unexpectedly, find and resolve the issue before loading any
BP charges!
Ground test the ejection charges. Prepare the rocket for
flight, loading ejection charges and igniters. Completely
assemble the air-frame and then use the 'Fire Igniters'
interface through a TeleDongle to command each charge to
fire. Make sure the charge is sufficient to robustly separate
the air-frame and deploy the recovery system.
Updating Device Firmware
The big concept to understand is that you have to use a
TeleDongle as a programmer to update a TeleMetrum or TeleMini,
and a TeleMetrum or other TeleDongle to program the TeleDongle
Due to limited memory resources in the cc1111, we don't support
programming directly over USB.
You may wish to begin by ensuring you have current firmware images.
These are distributed as part of the AltOS software bundle that
also includes the AltosUI ground station program. Newer ground
station versions typically work fine with older firmware versions,
so you don't need to update your devices just to try out new
software features. You can always download the most recent
version from .
We recommend updating the altimeter first, before updating TeleDongle.
Updating TeleMetrum Firmware
Find the 'programming cable' that you got as part of the starter
kit, that has a red 8-pin MicroMaTch connector on one end and a
red 4-pin MicroMaTch connector on the other end.
Take the 2 screws out of the TeleDongle case to get access
to the circuit board.
Plug the 8-pin end of the programming cable to the
matching connector on the TeleDongle, and the 4-pin end to the
matching connector on the TeleMetrum.
Note that each MicroMaTch connector has an alignment pin that
goes through a hole in the PC board when you have the cable
oriented correctly.
Attach a battery to the TeleMetrum board.
Plug the TeleDongle into your computer's USB port, and power
up the TeleMetrum.
Run AltosUI, and select 'Flash Image' from the File menu.
Pick the TeleDongle device from the list, identifying it as the
programming device.
Select the image you want put on the TeleMetrum, which should have a
name in the form telemetrum-v1.2-1.0.0.ihx. It should be visible
in the default directory, if not you may have to poke around
your system to find it.
Make sure the configuration parameters are reasonable
looking. If the serial number and/or RF configuration
values aren't right, you'll need to change them.
Hit the 'OK' button and the software should proceed to flash
the TeleMetrum with new firmware, showing a progress bar.
Confirm that the TeleMetrum board seems to have updated OK, which you
can do by plugging in to it over USB and using a terminal program
to connect to the board and issue the 'v' command to check
the version, etc.
If something goes wrong, give it another try.
Updating TeleMini Firmware
You'll need a special 'programming cable' to reprogram the
TeleMini. It's available on the Altus Metrum web store, or
you can make your own using an 8-pin MicroMaTch connector on
one end and a set of four pins on the other.
Take the 2 screws out of the TeleDongle case to get access
to the circuit board.
Plug the 8-pin end of the programming cable to the matching
connector on the TeleDongle, and the 4-pins into the holes
in the TeleMini circuit board. Note that the MicroMaTch
connector has an alignment pin that goes through a hole in
the PC board when you have the cable oriented correctly, and
that pin 1 on the TeleMini board is marked with a square pad
while the other pins have round pads.
Attach a battery to the TeleMini board.
Plug the TeleDongle into your computer's USB port, and power
up the TeleMini
Run AltosUI, and select 'Flash Image' from the File menu.
Pick the TeleDongle device from the list, identifying it as the
programming device.
Select the image you want put on the TeleMini, which should have a
name in the form telemini-v1.0-1.0.0.ihx. It should be visible
in the default directory, if not you may have to poke around
your system to find it.
Make sure the configuration parameters are reasonable
looking. If the serial number and/or RF configuration
values aren't right, you'll need to change them.
Hit the 'OK' button and the software should proceed to flash
the TeleMini with new firmware, showing a progress bar.
Confirm that the TeleMini board seems to have updated OK, which you
can do by configuring it over the radio link through the TeleDongle, or
letting it come up in "flight" mode and listening for telemetry.
If something goes wrong, give it another try.
Updating TeleDongle Firmware
Updating TeleDongle's firmware is just like updating TeleMetrum or TeleMini
firmware, but you use either a TeleMetrum or another TeleDongle as the programmer.
Find the 'programming cable' that you got as part of the starter
kit, that has a red 8-pin MicroMaTch connector on one end and a
red 4-pin MicroMaTch connector on the other end.
Find the USB cable that you got as part of the starter kit, and
plug the "mini" end in to the mating connector on TeleMetrum or TeleDongle.
Take the 2 screws out of the TeleDongle case to get access
to the circuit board.
Plug the 8-pin end of the programming cable to the
matching connector on the programmer, and the 4-pin end to the
matching connector on the TeleDongle.
Note that each MicroMaTch connector has an alignment pin that
goes through a hole in the PC board when you have the cable
oriented correctly.
Attach a battery to the TeleMetrum board if you're using one.
Plug both the programmer and the TeleDongle into your computer's USB
ports, and power up the programmer.
Run AltosUI, and select 'Flash Image' from the File menu.
Pick the programmer device from the list, identifying it as the
programming device.
Select the image you want put on the TeleDongle, which should have a
name in the form teledongle-v0.2-1.0.0.ihx. It should be visible
in the default directory, if not you may have to poke around
your system to find it.
Make sure the configuration parameters are reasonable
looking. If the serial number and/or RF configuration
values aren't right, you'll need to change them. The TeleDongle
serial number is on the "bottom" of the circuit board, and can
usually be read through the translucent blue plastic case without
needing to remove the board from the case.
Hit the 'OK' button and the software should proceed to flash
the TeleDongle with new firmware, showing a progress bar.
Confirm that the TeleDongle board seems to have updated OK, which you
can do by plugging in to it over USB and using a terminal program
to connect to the board and issue the 'v' command to check
the version, etc. Once you're happy, remove the programming cable
and put the cover back on the TeleDongle.
If something goes wrong, give it another try.
Be careful removing the programming cable from the locking 8-pin
connector on TeleMetrum. You'll need a fingernail or perhaps a thin
screwdriver or knife blade to gently pry the locking ears out
slightly to extract the connector. We used a locking connector on
TeleMetrum to help ensure that the cabling to companion boards
used in a rocket don't ever come loose accidentally in flight.
Hardware Specifications
TeleMetrum Specifications
Recording altimeter for model rocketry.
Supports dual deployment (can fire 2 ejection charges).
70cm ham-band transceiver for telemetry down-link.
Barometric pressure sensor good to 45k feet MSL.
1-axis high-g accelerometer for motor characterization, capable of
+/- 50g using default part.
On-board, integrated GPS receiver with 5Hz update rate capability.
On-board 1 megabyte non-volatile memory for flight data storage.
USB interface for battery charging, configuration, and data recovery.
Fully integrated support for Li-Po rechargeable batteries.
Uses Li-Po to fire e-matches, can be modified to support
optional separate pyro battery if needed.
2.75 x 1 inch board designed to fit inside 29mm air-frame coupler tube.
TeleMini Specifications
Recording altimeter for model rocketry.
Supports dual deployment (can fire 2 ejection charges).
70cm ham-band transceiver for telemetry down-link.
Barometric pressure sensor good to 45k feet MSL.
On-board 5 kilobyte non-volatile memory for flight data storage.
RF interface for configuration, and data recovery.
Support for Li-Po rechargeable batteries, using an external charger.
Uses Li-Po to fire e-matches, can be modified to support
optional separate pyro battery if needed.
1.5 x .5 inch board designed to fit inside 18mm air-frame coupler tube.
FAQ
TeleMetrum seems to shut off when disconnected from the
computer. Make sure the battery is adequately charged. Remember the
unit will pull more power than the USB port can deliver before the
GPS enters "locked" mode. The battery charges best when TeleMetrum
is turned off.
It's impossible to stop the TeleDongle when it's in "p" mode, I have
to unplug the USB cable? Make sure you have tried to "escape out" of
this mode. If this doesn't work the reboot procedure for the
TeleDongle *is* to simply unplug it. 'cu' however will retain it's
outgoing buffer IF your "escape out" ('~~') does not work.
At this point using either 'ao-view' (or possibly
'cutemon') instead of 'cu' will 'clear' the issue and allow renewed
communication.
The amber LED (on the TeleMetrum) lights up when both
battery and USB are connected. Does this mean it's charging?
Yes, the yellow LED indicates the charging at the 'regular' rate.
If the led is out but the unit is still plugged into a USB port,
then the battery is being charged at a 'trickle' rate.
There are no "dit-dah-dah-dit" sound or lights like the manual mentions?
That's the "pad" mode. Weak batteries might be the problem.
It is also possible that the TeleMetrum is horizontal and the output
is instead a "dit-dit" meaning 'idle'. For TeleMini, it's possible that
it received a command packet which would have left it in "pad" mode.
How do I save flight data?
Live telemetry is written to file(s) whenever AltosUI is connected
to the TeleDongle. The file area defaults to ~/TeleMetrum
but is easily changed using the menus in AltosUI. The files that
are written end in '.telem'. The after-flight
data-dumped files will end in .eeprom and represent continuous data
unlike the .telem files that are subject to losses
along the RF data path.
See the above instructions on what and how to save the eeprom stored
data after physically retrieving your altimeter. Make sure to save
the on-board data after each flight; while the TeleMetrum can store
multiple flights, you never know when you'll lose the altimeter...
Notes for Older Software
Before AltosUI was written, using Altus Metrum devices required
some finesse with the Linux command line. There was a limited
GUI tool, ao-view, which provided functionality similar to the
Monitor Flight window in AltosUI, but everything else was a
fairly 80's experience. This appendix includes documentation for
using that software.
Both TeleMetrum and TeleDongle can be directly communicated
with using USB ports. The first thing you should try after getting
both units plugged into to your computer's USB port(s) is to run
'ao-list' from a terminal-window to see what port-device-name each
device has been assigned by the operating system.
You will need this information to access the devices via their
respective on-board firmware and data using other command line
programs in the AltOS software suite.
TeleMini can be communicated with through a TeleDongle device
over the radio link. When first booted, TeleMini listens for a
TeleDongle device and if it receives a packet, it goes into
'idle' mode. Otherwise, it goes into 'pad' mode and waits to be
launched. The easiest way to get it talking is to start the
communication link on the TeleDongle and the power up the
TeleMini board.
To access the device's firmware for configuration you need a terminal
program such as you would use to talk to a modem. The software
authors prefer using the program 'cu' which comes from the UUCP package
on most Unix-like systems such as Linux. An example command line for
cu might be 'cu -l /dev/ttyACM0', substituting the correct number
indicated from running the
ao-list program. Another reasonable terminal program for Linux is
'cutecom'. The default 'escape'
character used by CU (i.e. the character you use to
issue commands to cu itself instead of sending the command as input
to the connected device) is a '~'. You will need this for use in
only two different ways during normal operations. First is to exit
the program by sending a '~.' which is called a 'escape-disconnect'
and allows you to close-out from 'cu'. The
second use will be outlined later.
All of the Altus Metrum devices share the concept of a two level
command set in their firmware.
The first layer has several single letter commands. Once
you are using 'cu' (or 'cutecom') sending (typing) a '?'
returns a full list of these
commands. The second level are configuration sub-commands accessed
using the 'c' command, for
instance typing 'c?' will give you this second level of commands
(all of which require the
letter 'c' to access). Please note that most configuration options
are stored only in Flash memory; TeleDongle doesn't provide any storage
for these options and so they'll all be lost when you unplug it.
Try setting these configuration ('c' or second level menu) values. A good
place to start is by setting your call sign. By default, the boards
use 'N0CALL' which is cute, but not exactly legal!
Spend a few minutes getting comfortable with the units, their
firmware, and 'cu' (or possibly 'cutecom').
For instance, try to send
(type) a 'c r 2' and verify the channel change by sending a 'c s'.
Verify you can connect and disconnect from the units while in your
terminal program by sending the escape-disconnect mentioned above.
To set the radio frequency, use the 'c R' command to specify the
radio transceiver configuration parameter. This parameter is computed
using the desired frequency, 'F', the radio calibration parameter, 'C' (showed by the 'c s' command) and
the standard calibration reference frequency, 'S', (normally 434.550MHz):
R = F / S * C
Round the result to the nearest integer value.
As with all 'c' sub-commands, follow this with a 'c w' to write the
change to the parameter block in the on-board flash on
your altimeter board if you want the change to stay in place across reboots.
To set the apogee delay, use the 'c d' command.
As with all 'c' sub-commands, follow this with a 'c w' to write the
change to the parameter block in the on-board DataFlash chip.
To set the main deployment altitude, use the 'c m' command.
As with all 'c' sub-commands, follow this with a 'c w' to write the
change to the parameter block in the on-board DataFlash chip.
To calibrate the radio frequency, connect the UHF antenna port to a
frequency counter, set the board to 434.550MHz, and use the 'C'
command to generate a CW carrier. Wait for the transmitter temperature
to stabilize and the frequency to settle down.
Then, divide 434.550 MHz by the
measured frequency and multiply by the current radio cal value show
in the 'c s' command. For an unprogrammed board, the default value
is 1186611. Take the resulting integer and program it using the 'c f'
command. Testing with the 'C' command again should show a carrier
within a few tens of Hertz of the intended frequency.
As with all 'c' sub-commands, follow this with a 'c w' to write the
change to the parameter block in the on-board DataFlash chip.
Note that the 'reboot' command, which is very useful on the altimeters,
will likely just cause problems with the dongle. The *correct* way
to reset the dongle is just to unplug and re-plug it.
A fun thing to do at the launch site and something you can do while
learning how to use these units is to play with the radio link access
between an altimeter and the TeleDongle. Be aware that you *must* create
some physical separation between the devices, otherwise the link will
not function due to signal overload in the receivers in each device.
Now might be a good time to take a break and read the rest of this
manual, particularly about the two "modes" that the altimeters
can be placed in. TeleMetrum uses the position of the device when booting
up will determine whether the unit is in "pad" or "idle" mode. TeleMini
enters "idle" mode when it receives a command packet within the first 5 seconds
of being powered up, otherwise it enters "pad" mode.
You can access an altimeter in idle mode from the TeleDongle's USB
connection using the radio link
by issuing a 'p' command to the TeleDongle. Practice connecting and
disconnecting ('~~' while using 'cu') from the altimeter. If
you cannot escape out of the "p" command, (by using a '~~' when in
CU) then it is likely that your kernel has issues. Try a newer version.
Using this radio link allows you to configure the altimeter, test
fire e-matches and igniters from the flight line, check pyro-match
continuity and so forth. You can leave the unit turned on while it
is in 'idle mode' and then place the
rocket vertically on the launch pad, walk away and then issue a
reboot command. The altimeter will reboot and start sending data
having changed to the "pad" mode. If the TeleDongle is not receiving
this data, you can disconnect 'cu' from the TeleDongle using the
procedures mentioned above and THEN connect to the TeleDongle from
inside 'ao-view'. If this doesn't work, disconnect from the
TeleDongle, unplug it, and try again after plugging it back in.
In order to reduce the chance of accidental firing of pyrotechnic
charges, the command to fire a charge is intentionally somewhat
difficult to type, and the built-in help is slightly cryptic to
prevent accidental echoing of characters from the help text back at
the board from firing a charge. The command to fire the apogee
drogue charge is 'i DoIt drogue' and the command to fire the main
charge is 'i DoIt main'.
On TeleMetrum, the GPS will eventually find enough satellites, lock in on them,
and 'ao-view' will both auditorily announce and visually indicate
that GPS is ready.
Now you can launch knowing that you have a good data path and
good satellite lock for flight data and recovery. Remember
you MUST tell ao-view to connect to the TeleDongle explicitly in
order for ao-view to be able to receive data.
The altimeters provide RDF (radio direction finding) tones on
the pad, during descent and after landing. These can be used to
locate the rocket using a directional antenna; the signal
strength providing an indication of the direction from receiver to rocket.
TeleMetrum also provides GPS tracking data, which can further simplify
locating the rocket once it has landed. (The last good GPS data
received before touch-down will be on the data screen of 'ao-view'.)
Once you have recovered the rocket you can download the eeprom
contents using either 'ao-dumplog' (or possibly 'ao-eeprom'), over
either a USB cable or over the radio link using TeleDongle.
And by following the man page for 'ao-postflight' you can create
various data output reports, graphs, and even KML data to see the
flight trajectory in Google-earth. (Moving the viewing angle making
sure to connect the yellow lines while in Google-earth is the proper
technique.)
As for ao-view.... some things are in the menu but don't do anything
very useful. The developers have stopped working on ao-view to focus
on a new, cross-platform ground station program. So ao-view may or
may not be updated in the future. Mostly you just use
the Log and Device menus. It has a wonderful display of the incoming
flight data and I am sure you will enjoy what it has to say to you
once you enable the voice output!
Drill Templates
These images, when printed, provide precise templates for the
mounting holes in Altus Metrum flight computers
TeleMetrum template
TeleMetrum has overall dimensions of 1.000 x 2.750 inches, and the
mounting holes are sized for use with 4-40 or M3 screws.
TeleMini template
TeleMini has overall dimensions of 0.500 x 1.500 inches, and the
mounting holes are sized for use with 2-56 or M2 screws.
Calibration
There are only two calibrations required for a TeleMetrum board, and
only one for TeleDongle and TeleMini. All boards are shipped from
the factory pre-calibrated, but the procedures are documented here
in case they are ever needed. Re-calibration is not supported by
AltosUI, you must connect to the board with a serial terminal program
and interact directly with the on-board command interpreter to effect
calibration.
Radio Frequency
The radio frequency is synthesized from a clock based on the 48 MHz
crystal on the board. The actual frequency of this oscillator
must be measured to generate a calibration constant. While our
GFSK modulation
bandwidth is wide enough to allow boards to communicate even when
their oscillators are not on exactly the same frequency, performance
is best when they are closely matched.
Radio frequency calibration requires a calibrated frequency counter.
Fortunately, once set, the variation in frequency due to aging and
temperature changes is small enough that re-calibration by customers
should generally not be required.
To calibrate the radio frequency, connect the UHF antenna port to a
frequency counter, set the board to 434.550MHz, and use the 'C'
command in the on-board command interpreter to generate a CW
carrier. For TeleMetrum, this is best done over USB. For TeleMini,
note that the only way to escape the 'C' command is via power cycle
since the board will no longer be listening for commands once it
starts generating a CW carrier.
Wait for the transmitter temperature to stabilize and the frequency
to settle down. Then, divide 434.550 MHz by the
measured frequency and multiply by the current radio cal value show
in the 'c s' command. For an unprogrammed board, the default value
is 1186611. Take the resulting integer and program it using the 'c f'
command. Testing with the 'C' command again should show a carrier
within a few tens of Hertz of the intended frequency.
As with all 'c' sub-commands, follow this with a 'c w' to write the
change to the parameter block in the on-board DataFlash chip.
Note that any time you re-do the radio frequency calibration, the
radio frequency is reset to the default 434.550 Mhz. If you want
to use another frequency, you will have to set that again after
calibration is completed.
TeleMetrum Accelerometer
The TeleMetrum accelerometer we use has its own 5 volt power
supply and
the output must be passed through a resistive voltage divider to match
the input of our 3.3 volt ADC. This means that unlike the barometric
sensor, the output of the acceleration sensor is not ratio-metric to
the ADC converter, and calibration is required. Explicitly
calibrating the accelerometers also allows us to load any device
from a Freescale family that includes at least +/- 40g, 50g, 100g,
and 200g parts. Using gravity,
a simple 2-point calibration yields acceptable results capturing both
the different sensitivities and ranges of the different accelerometer
parts and any variation in power supply voltages or resistor values
in the divider network.
To calibrate the acceleration sensor, use the 'c a 0' command. You
will be prompted to orient the board vertically with the UHF antenna
up and press a key, then to orient the board vertically with the
UHF antenna down and press a key. Note that the accuracy of this
calibration depends primarily on how perfectly vertical and still
the board is held during the cal process. As with all 'c'
sub-commands, follow this with a 'c w' to write the
change to the parameter block in the on-board DataFlash chip.
The +1g and -1g calibration points are included in each telemetry
frame and are part of the header stored in onboard flash to be
downloaded after flight. We always store and return raw ADC
samples for each sensor... so nothing is permanently "lost" or
"damaged" if the calibration is poor.
In the unlikely event an accel cal goes badly, it is possible
that TeleMetrum may always come up in 'pad mode' and as such not be
listening to either the USB or radio link. If that happens,
there is a special hook in the firmware to force the board back
in to 'idle mode' so you can re-do the cal. To use this hook, you
just need to ground the SPI clock pin at power-on. This pin is
available as pin 2 on the 8-pin companion connector, and pin 1 is
ground. So either carefully install a fine-gauge wire jumper
between the two pins closest to the index hole end of the 8-pin
connector, or plug in the programming cable to the 8-pin connector
and use a small screwdriver or similar to short the two pins closest
to the index post on the 4-pin end of the programming cable, and
power up the board. It should come up in 'idle mode' (two beeps),
allowing a re-cal.
Release Notes
Version 1.1.1
Version 1.1
Version 1.0.1
Version 0.9.2
Version 0.9
Version 0.8
Version 0.7.1