simultaneously.
</para>
</section>
+ <section>
+ <title>Maximum Flight Log</title>
+ <para>
+ TeleMetrum version 1.1 has 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, there's plenty of space to store many flights worth
+ of data.
+ </para>
+ <para>
+ 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.
+ </para>
+ <para>
+ All of the configuration data is also stored in the flash
+ memory, which consumes 64kB on TeleMetrum v1.1 and 256B on
+ TeleMetrum v1.0. This configuration space is not available
+ for storing flight log data.
+ </para>
+ <para>
+ 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.
+ </para>
+ <para>
+ The default size, 192kB, allows for 10 flights of storage on
+ TeleMetrum v1.1 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.
+ </para>
+ </section>
+ <section>
+ <title>Ignite Mode</title>
+ <para>
+ 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.
+ </para>
+ <para>
+ 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.
+ </para>
+ </section>
+ <section>
+ <title>Pad Orientation</title>
+ <para>
+ 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.
+ </para>
+ </section>
</section>
- <section>
- <title>Calibration</title>
- <para>
- There are only two calibrations required for a TeleMetrum board, and
- only one for TeleDongle and TeleMini.
- </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>
- When the radio calibration value is changed, the radio
- frequency value is reset to the same value, so you'll need
- to recompute and reset the radio frequency value using the
- new radio calibration value.
- </para>
- </section>
- <section>
- <title>TeleMetrum Accelerometer</title>
- <para>
- 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. 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>
- <para>
- In the unlikely event an accel cal that 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).
- </para>
- </section>
- </section>
</chapter>
<chapter>
projects / fw / altos / commitdiff