</chapter>
<chapter>
<title>Specifications</title>
-
<itemizedlist>
<listitem>
- <para>
- Recording altimeter for model rocketry.
- </para>
+ Recording altimeter for model rocketry.
+ </para>
</listitem>
<listitem>
- <para>
- Supports dual deployment (can fire 2 ejection charges).
- </para>
+ Supports dual deployment (can fire 2 ejection charges).
+ </para>
</listitem>
<listitem>
- <para>
- 70cm ham-band transceiver for telemetry downlink.
- </para>
+ 70cm ham-band transceiver for telemetry downlink.
+ </para>
</listitem>
<listitem>
- <para>
- Barometric pressure sensor good to 45k feet MSL.
- </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>
+ 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>
+ 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>
+ 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>
+ USB interface for battery charging, configuration, and data recovery.
+ </para>
</listitem>
<listitem>
- <para>
- Fully integrated support for LiPo rechargeable batteries.
- </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>
+ 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>
+ 2.75 x 1 inch board designed to fit inside 29mm airframe coupler tube.
+ </para>
</listitem>
</itemizedlist>
</chapter>
<title>Handling Precautions</title>
<para>
TeleMetrum is a sophisticated electronic device. When handled gently and
- properly installed in an airframe, it will deliver extraordinary results.
+ properly installed in an airframe, it will deliver impressive results.
However, like all electronic devices, there are some precautions you
must take.
</para>
</para>
<para>
By default, we use the unregulated output of the LiPo battery directly
- to fire ejection charges. This works marvelously with standard e-matches
- from companies like [insert company and product names for e-matches we've
- tried and like] and with Quest Q2G2 igniters. However, if you
+ 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
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 by default and so may be the most familiar
+ 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
</chapter>
<chapter>
<title>Operation</title>
- <para>
- Placeholder.
- </para>
+ <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>
<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.
+
<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>
</para>
</section>
</section>
+ <section>
+ <title>
+ How GPS Works
+ </title>
+ <para>
+ Placeholder.
+ </para>
+ </section>
</chapter>
</book>
projects / fw / altos / blobdiff