<chapter>
<title>Introduction and Overview</title>
<para>
- Placeholder.
+ 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!
+ </para>
+ <para>
+ The focal point of our community is 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.
+ </para>
+ <para>
+ Complementing TeleMetrum is TeleDongle, a USB to RF interface for
+ communicating with TeleMetrum. 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.
</para>
</chapter>
<chapter>
<title>Specifications</title>
- <para>
- Placeholder.
- </para>
+ <itemizedlist>
+ <listitem>
+ <para>
+ Recording altimeter for model rocketry.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ Supports dual deployment (can fire 2 ejection charges).
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ 70cm ham-band transceiver for telemetry downlink.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ Barometric pressure sensor good to 45k feet MSL.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ 1-axis high-g accelerometer for motor characterization, capable of
+ +/- 50g using default part.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ On-board, integrated GPS receiver with 5hz update rate capability.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ On-board 1 megabyte non-volatile memory for flight data storage.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ USB interface for battery charging, configuration, and data recovery.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ Fully integrated support for LiPo rechargeable batteries.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ Uses LiPo to fire e-matches, support for optional separate pyro
+ battery if needed.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ 2.75 x 1 inch board designed to fit inside 29mm airframe coupler tube.
+ </para>
+ </listitem>
+ </itemizedlist>
</chapter>
<chapter>
<title>Handling Precautions</title>
<para>
- Placeholder.
+ TeleMetrum is a sophisticated electronic device. When handled gently and
+ properly installed in an airframe, it will deliver impressive results.
+ However, like all electronic devices, there are some precautions you
+ must take.
+ </para>
+ <para>
+ The Lithium Polymer rechargeable batteries used with TeleMetrum 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 airframe. We
+ often wrap them in suitable scraps of closed-cell packing foam before
+ strapping them down, for example.
+ </para>
+ <para>
+ The TeleMetrum barometric sensor is sensitive to sunlight. In normal
+ 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 a 29mm airframe's see-through
+ plastic payload bay.
+ </para>
+ <para>
+ The TeleMetrum 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, but also by having a
+ suitable static vent to outside air.
+ </para>
+ <para>
+ As with all other rocketry electronics, TeleMetrum must be protected
+ from exposure to corrosive motor exhaust and ejection charge gasses.
</para>
</chapter>
<chapter>
<title>Hardware Overview</title>
<para>
- Placeholder.
+ TeleMetrum is a 1 inch by 2.75 inch circuit board. It was designed to
+ fit inside coupler for 29mm airframe tubing, but using it in a tube that
+ small in diameter may require some creativity in mounting and wiring
+ to succeed! The default 1/4
+ wave UHF wire antenna attached to the center of the nose-cone 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
+ fin can end of the board. Given all this, an ideal "simple" avionics
+ bay for TeleMetrum should have at least 10 inches of interior length.
</para>
- </chapter>
- <chapter>
- <title>Operation</title>
<para>
- Placeholder.
+ A typical TeleMetrum installation using the on-board GPS antenna and
+ default wire UHF antenna 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.
</para>
- </chapter>
- <chapter>
- <title>System Overview</title>
<para>
- Placeholder.
+ By default, we use the unregulated output of the LiPo 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, you can do so by adding
+ a second 2mm connector to position B2 on the board and cutting the
+ thick pcb trace connecting the LiPo battery to the pyro circuit between
+ the two silk screen marks on the surface mount side of the board shown
+ here [insert photo]
</para>
- </chapter>
- <chapter>
- <title>System Overview</title>
<para>
- Placeholder.
+ We offer two choices of pyro and power switch connector, or you can
+ choose neither and solder wires directly to the board. All three choices
+ are reasonable depending on the constraints of your airframe. Our
+ favorite option when there is sufficient room above the board is to use
+ the Tyco pin header with polarization and locking. If you choose this
+ option, you crimp individual wires for the power switch and e-matches
+ into a mating connector, and installing and removing the TeleMetrum
+ board from an airframe is as easy as plugging or unplugging two
+ connectors. If the airframe will not support this much height or if
+ you want to be able to directly attach e-match leads to the board, we
+ offer a screw terminal block. This is very similar to what most other
+ altimeter vendors provide and so may be the most familiar
+ option. You'll need a very small straight blade screwdriver to connect
+ and disconnect the board in this case, such as you might find in a
+ jeweler's screwdriver set. Finally, you can forego both options and
+ solder wires directly to the board, which may be the best choice for
+ minimum diameter and/or minimum mass designs.
</para>
+ <para>
+ For most airframes, the integrated GPS antenna and wire UHF antenna are
+ a great combination. However, if you are installing in a carbon-fiber
+ electronics bay which is opaque to RF signals, you may need to use
+ off-board external antennas instead. In this case, you can order
+ TeleMetrum with an SMA connector for the UHF antenna connection, and
+ you can unplug the integrated GPS antenna and select an appropriate
+ off-board GPS antenna with cable terminating in a U.FL connector.
+ </para>
+ </chapter>
+ <chapter>
+ <title>Operation</title>
+ <section>
+ <title>Firmware Modes </title>
+<para>
+ The AltOS firmware build for TeleMetrum has two fundamental modes,
+ "idle" and "flight". Which of these modes the firmware operates in
+ is determined 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.
+</para>
+<para>
+ At power on, you will hear three beeps ("S" in Morse code for startup)
+ and then a pause while
+ TeleMetrum completes initialization and self tests, and decides which
+ mode to enter next.
+</para>
+<para>
+ In flight mode, TeleMetrum turns on the GPS system, engages the flight
+ state machine, goes into transmit-only mode on the RF link sending
+ telemetry, and waits for launch to be detected. Flight mode is
+ indicated by an audible "di-dah-dah-dit" ("P" for pad) on the
+ beeper, followed by
+ beeps indicating the state of the pyrotechnic igniter continuity.
+ One beep indicates apogee continuity, two beeps indicate
+ main continuity, three beeps indicate both apogee and main continuity,
+ and one longer "brap" sound indicates no continuity. For a dual
+ deploy flight, make sure you're getting three beeps before launching!
+ For apogee-only or motor eject flights, do what makes sense.
+</para>
+<para>
+ In idle mode, you will hear an audible "di-dit" ("I" for idle), and
+ the normal flight state machine is disengaged, thus
+ no ejection charges will fire. TeleMetrum also listens on the RF
+ link when in idle mode for packet mode requests sent from TeleDongle.
+ Commands can be issued to a TeleMetrum in idle mode over either
+ USB or the RF link equivalently.
+ Idle mode is useful for configuring TeleMetrum, for extracting data
+ from the on-board storage chip after flight, and for ground testing
+ pyro charges.
+</para>
+<para>
+ One "neat trick" of particular value when TeleMetrum is used with very
+ large airframes, 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 airframe to launch position, use a TeleDongle to open
+ a packet connection, and issue a 'reset' command which will cause
+ TeleMetrum to reboot, realize it's now nose-up, and thus choose
+ 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!
+</para>
+ </section>
+ <section>
+ <title>GPS </title>
+<para>
+ TeleMetrum includes a complete GPS receiver. See a later section for
+ a brief explanation of how GPS works that will help you understand
+ the information in the telemetry stream. 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!
+</para>
+<para>
+ TeleMetrum provides backup power to the GPS chip any time a LiPo
+ battery is connected. This allows the receiver to "warm start" on
+ the launch rail much faster than if every power-on were a "cold start"
+ for the GPS receiver. In typical operations, powering up TeleMetrum
+ on the flight line in idle mode while performing final airframe
+ 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.
+</para>
+ </section>
+ <section>
+ <title>Ground Testing </title>
+ <para>
+ An important aspect of preparing a rocket using electronic deployment
+ for flight is ground testing the recovery system. Thanks
+ to the bi-directional RF link central to the Altus Metrum system,
+ this can be accomplished in a TeleMetrum-equipped rocket without as
+ much work as you may be accustomed to with other systems. It can
+ even be fun!
+ </para>
+ <para>
+ Just prep the rocket for flight, then power up TeleMetrum while the
+ airframe is horizontal. 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. Then, establish an
+ RF packet connection from a TeleDongle-equipped computer using the
+ P command from a safe distance. You can now command TeleMetrum to
+ fire the apogee or main charges to complete your testing.
+ </para>
+ <para>
+ 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'.
+ </para>
+ </section>
+ <section>
+ <title>Radio Link </title>
+ <para>
+ 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.
+ </para>
+ <para>
+ By design, TeleMetrum firmware listens for an RF connection when
+ it's in "idle mode" (turned on while the rocket is horizontal), which
+ allows us to use the RF link to configure the rocket, do things like
+ ejection tests, and extract data after a flight without having to
+ crack open the airframe. However, when the board is in "flight
+ mode" (turned on when the rocket is vertical) the TeleMetrum 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 and out over
+ the RF link in case the rocket crashes and we aren't able to extract
+ data later...
+ </para>
+ <para>
+ We don't use a 'normal packet radio' mode because they're just too
+ inefficient. The GFSK modulation we use is just FSK with the
+ baseband 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 a test flight above 12k AGL with good reception, and calculations
+ suggest we should be good to 40k AGL or more with a 5-element yagi on
+ the ground. We hope to fly boards to higher altitudes soon, and would
+ of course appreciate customer feedback on performance in higher
+ altitude flights!
+ </para>
+ </section>
+ <section>
+ <title>Configurable Parameters</title>
+ <para>
+ Configuring a TeleMetrum board for flight is very simple. Because we
+ have both acceleration and pressure sensors, there is no need to set
+ a "mach delay", for example. The few configurable parameters can all
+ be set using a simple terminal program over the USB port or RF link
+ via TeleDongle.
+ </para>
+ <section>
+ <title>Radio Channel</title>
+ <para>
+ Our firmware supports 10 channels. The default channel 0 corresponds
+ to a center frequency of 434.550 Mhz, and channels are spaced every
+ 100 khz. Thus, channel 1 is 434.650 Mhz, and channel 9 is 435.550 Mhz.
+ At any given launch, we highly recommend coordinating who will use
+ each channel and when to avoid interference. And of course, both
+ TeleMetrum and TeleDongle must be configured to the same channel to
+ successfully communicate with each other.
+ </para>
+ <para>
+ To set the radio channel, use the 'c r' command, like 'c r 3' to set
+ channel 3.
+ 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.
+ </para>
+ </section>
+ <section>
+ <title>Apogee Delay</title>
+ <para>
+ Apogee delay is the number of seconds after TeleMetrum 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.
+ </para>
+ <para>
+ To set the apogee delay, use the [FIXME] 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.
+ </para>
+ </section>
+ <section>
+ <title>Main Deployment Altitude</title>
+ <para>
+ By default, TeleMetrum 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 airframes, 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.
+ </para>
+ <para>
+ To set the main deployment altitude, use the [FIXME] 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.
+ </para>
+ </section>
+ </section>
+ <section>
+ <title>Calibration</title>
+ <para>
+ There are only two calibrations required for a TeleMetrum board, and
+ only one for TeleDongle.
+ </para>
+ <section>
+ <title>Radio Frequency</title>
+ <para>
+ 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.
+ </para>
+ <para>
+ To calibrate the radio frequency, connect the UHF antenna port to a
+ frequency counter, set the board to channel 0, 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.
+ </para>
+ </section>
+ <section>
+ <title>Accelerometer</title>
+ <para>
+ The 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 ratiometric to
+ the ADC converter, and calibration is required. We also support the
+ use of any of several accelerometers 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.
+ </para>
+ <para>
+ 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.
+ 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.
+ </para>
+ <para>
+ The +1g and -1g calibration points are included in each telemetry
+ frame and are part of the header extracted by ao-dumplog after flight.
+ Note that we always store and return raw ADC samples for each
+ sensor... nothing is permanently "lost" or "damaged" if the
+ calibration is poor.
+ </para>
+ </section>
+ </section>
+ </chapter>
+ <chapter>
+ <title>Using Altus Metrum Products</title>
+ <section>
+ <title>Being Legal</title>
+ <para>
+ First off, in the US, you need an [amateur radio license](../Radio) or
+ other authorization to legally operate the radio transmitters that are part
+ of our products.
+ </para>
+ <section>
+ <title>In the Rocket</title>
+ <para>
+ In the rocket itself, you just need a [TeleMetrum](../TeleMetrum) board and
+ a LiPo rechargeable battery. An 860mAh battery weighs less than a 9V
+ alkaline battery, and will run a [TeleMetrum](../TeleMetrum) for hours.
+ </para>
+ <para>
+ By default, we ship TeleMetrum with a simple wire antenna. If your
+ electronics bay or the airframe 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.
+ </para>
+ </section>
+ <section>
+ <title>On the Ground</title>
+ <para>
+ To receive the data stream from the rocket, you need an antenna and short
+ feedline connected to one of our [TeleDongle](../TeleDongle) units. 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.
+ </para>
+ <para>
+ Right now, all of our application software is written for Linux. However,
+ because we understand that many people run Windows or MacOS, we are working
+ on a new ground station program written in Java that should work on all
+ operating systems.
+ </para>
+ <para>
+ After the flight, you can use the RF link to extract the more detailed data
+ logged in the rocket, 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 LiPo
+ 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.
+ </para>
+ <para>
+ If your rocket lands out of sight, you may enjoy having a hand-held GPS
+ receiver, so that you can put in a waypoint for the last reported rocket
+ position before touch-down. This makes looking for your rocket a lot like
+ Geo-Cacheing... just go to the waypoint and look around starting from there.
+ </para>
+ <para>
+ 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.
+ </para>
+ <para>
+ So, to recap, on the ground the hardware you'll need includes:
+ <orderedlist inheritnum='inherit' numeration='arabic'>
+ <listitem>
+ an antenna and feedline
+ </listitem>
+ <listitem>
+ a TeleDongle
+ </listitem>
+ <listitem>
+ a notebook computer
+ </listitem>
+ <listitem>
+ optionally, a handheld GPS receiver
+ </listitem>
+ <listitem>
+ optionally, an HT or receiver covering 435 Mhz
+ </listitem>
+ </orderedlist>
+ </para>
+ <para>
+ The best hand-held commercial directional antennas we've found for radio
+ direction finding rockets are from
+ <ulink url="http://www.arrowantennas.com/" >
+ Arrow Antennas.
+ </ulink>
+ The 440-3 and 440-5 are both good choices for finding a
+ TeleMetrum-equipped rocket when used with a suitable 70cm HT.
+ </para>
+ </section>
+ <section>
+ <title>Data Analysis</title>
+ <para>
+ Our software makes it easy to log the data from each flight, both the
+ telemetry received over the RF link during the flight itself, and the more
+ complete data log recorded in the DataFlash memory on the TeleMetrum
+ board. Once this data is on your computer, our postflight 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 data file
+ useable with Google Maps and Google Earth for visualizing the flight path
+ in two or three dimensions!
+ </para>
+ <para>
+ 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.
+ </para>
+ </section>
+ <section>
+ <title>Future Plans</title>
+ <para>
+ 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. A reference design for a companion board will be documented
+ soon, and will be compatible with open source Arduino programming tools.
+ </para>
+ <para>
+ We are also working on the design of a 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.
+ </para>
+ <para>
+ 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...
+ </para>
+ </section>
+ </section>
+ <section>
+ <title>
+ How GPS Works
+ </title>
+ <para>
+ Placeholder.
+ </para>
+ </section>
</chapter>
</book>
projects / fw / altos / blobdiff