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7 <firstname>Bdale</firstname>
8 <surname>Garbee</surname>
11 <firstname>Keith</firstname>
12 <surname>Packard</surname>
16 <holder>Bdale Garbee and Keith Packard</holder>
18 <title>TeleMetrum</title>
19 <subtitle>Owner's Manual for the TeleMetrum System</subtitle>
22 This document is released under the terms of the
23 <ulink url="http://creativecommons.org/licenses/by-sa/3.0/">
24 Creative Commons ShareAlike 3.0
31 <revnumber>0.1</revnumber>
32 <date>30 March 2010</date>
33 <revremark>Initial content</revremark>
38 <title>Introduction and Overview</title>
40 Welcome to the Altus Metrum community! Our circuits and software reflect
41 our passion for both hobby rocketry and Free Software. We hope their
42 capabilities and performance will delight you in every way, but by
43 releasing all of our hardware and software designs under open licenses,
44 we also hope to empower you to take as active a role in our collective
48 The focal point of our community is TeleMetrum, a dual deploy altimeter
49 with fully integrated GPS and radio telemetry as standard features, and
50 a "companion interface" that will support optional capabilities in the
54 Complementing TeleMetrum is TeleDongle, a USB to RF interface for
55 communicating with TeleMetrum. Combined with your choice of antenna and
56 notebook computer, TeleDongle and our associated user interface software
57 form a complete ground station capable of logging and displaying in-flight
58 telemetry, aiding rocket recovery, then processing and archiving flight
59 data for analysis and review.
63 <title>Specifications</title>
67 Recording altimeter for model rocketry.
72 Supports dual deployment (can fire 2 ejection charges).
77 70cm ham-band transceiver for telemetry downlink.
82 Barometric pressure sensor good to 45k feet MSL.
87 1-axis high-g accelerometer for motor characterization, capable of
88 +/- 50g using default part.
93 On-board, integrated GPS receiver with 5hz update rate capability.
98 On-board 1 megabyte non-volatile memory for flight data storage.
103 USB interface for battery charging, configuration, and data recovery.
108 Fully integrated support for LiPo rechargeable batteries.
113 Uses LiPo to fire e-matches, support for optional separate pyro
119 2.75 x 1 inch board designed to fit inside 29mm airframe coupler tube.
125 <title>Handling Precautions</title>
127 TeleMetrum is a sophisticated electronic device. When handled gently and
128 properly installed in an airframe, it will deliver impressive results.
129 However, like all electronic devices, there are some precautions you
133 The Lithium Polymer rechargeable batteries used with TeleMetrum have an
134 extraordinary power density. This is great because we can fly with
135 much less battery mass than if we used alkaline batteries or previous
136 generation rechargeable batteries... but if they are punctured
137 or their leads are allowed to short, they can and will release their
139 Thus we recommend that you take some care when handling our batteries
140 and consider giving them some extra protection in your airframe. We
141 often wrap them in suitable scraps of closed-cell packing foam before
142 strapping them down, for example.
145 The TeleMetrum barometric sensor is sensitive to sunlight. In normal
146 mounting situations, it and all of the other surface mount components
147 are "down" towards whatever the underlying mounting surface is, so
148 this is not normally a problem. Please consider this, though, when
149 designing an installation, for example, in a 29mm airframe's see-through
153 The TeleMetrum barometric sensor sampling port must be able to "breathe",
154 both by not being covered by foam or tape or other materials that might
155 directly block the hole on the top of the sensor, but also by having a
156 suitable static vent to outside air.
159 As with all other rocketry electronics, TeleMetrum must be protected
160 from exposure to corrosive motor exhaust and ejection charge gasses.
164 <title>Hardware Overview</title>
166 TeleMetrum is a 1 inch by 2.75 inch circuit board. It was designed to
167 fit inside coupler for 29mm airframe tubing, but using it in a tube that
168 small in diameter may require some creativity in mounting and wiring
169 to succeed! The default 1/4
170 wave UHF wire antenna attached to the center of the nose-cone end of
171 the board is about 7 inches long, and wiring for a power switch and
172 the e-matches for apogee and main ejection charges depart from the
173 fin can end of the board. Given all this, an ideal "simple" avionics
174 bay for TeleMetrum should have at least 10 inches of interior length.
177 A typical TeleMetrum installation using the on-board GPS antenna and
178 default wire UHF antenna involves attaching only a suitable
179 Lithium Polymer battery, a single pole switch for power on/off, and
180 two pairs of wires connecting e-matches for the apogee and main ejection
184 By default, we use the unregulated output of the LiPo battery directly
185 to fire ejection charges. This works marvelously with standard
186 low-current e-matches like the J-Tek from MJG Technologies, and with
187 Quest Q2G2 igniters. However, if you
188 want or need to use a separate pyro battery, you can do so by adding
189 a second 2mm connector to position B2 on the board and cutting the
190 thick pcb trace connecting the LiPo battery to the pyro circuit between
191 the two silk screen marks on the surface mount side of the board shown
195 We offer two choices of pyro and power switch connector, or you can
196 choose neither and solder wires directly to the board. All three choices
197 are reasonable depending on the constraints of your airframe. Our
198 favorite option when there is sufficient room above the board is to use
199 the Tyco pin header with polarization and locking. If you choose this
200 option, you crimp individual wires for the power switch and e-matches
201 into a mating connector, and installing and removing the TeleMetrum
202 board from an airframe is as easy as plugging or unplugging two
203 connectors. If the airframe will not support this much height or if
204 you want to be able to directly attach e-match leads to the board, we
205 offer a screw terminal block. This is very similar to what most other
206 altimeter vendors provide and so may be the most familiar
207 option. You'll need a very small straight blade screwdriver to connect
208 and disconnect the board in this case, such as you might find in a
209 jeweler's screwdriver set. Finally, you can forego both options and
210 solder wires directly to the board, which may be the best choice for
211 minimum diameter and/or minimum mass designs.
214 For most airframes, the integrated GPS antenna and wire UHF antenna are
215 a great combination. However, if you are installing in a carbon-fiber
216 electronics bay which is opaque to RF signals, you may need to use
217 off-board external antennas instead. In this case, you can order
218 TeleMetrum with an SMA connector for the UHF antenna connection, and
219 you can unplug the integrated GPS antenna and select an appropriate
220 off-board GPS antenna with cable terminating in a U.FL connector.
224 <title>Operation</title>
226 <title>Firmware Modes </title>
228 The AltOS firmware build for TeleMetrum has two fundamental modes,
229 "idle" and "flight". Which of these modes the firmware operates in
230 is determined by the orientation of the rocket (well, actually the
231 board, of course...) at the time power is switched on. If the rocket
232 is "nose up", then TeleMetrum assumes it's on a rail or rod being
233 prepared for launch, so the firmware chooses flight mode. However,
234 if the rocket is more or less horizontal, the firmware instead enters
238 At power on, you will hear three beeps ("S" in Morse code for startup)
239 and then a pause while
240 TeleMetrum completes initialization and self tests, and decides which
244 In flight mode, TeleMetrum turns on the GPS system, engages the flight
245 state machine, goes into transmit-only mode on the RF link sending
246 telemetry, and waits for launch to be detected. Flight mode is
247 indicated by an audible "di-dah-dah-dit" ("P" for pad) on the
249 beeps indicating the state of the pyrotechnic igniter continuity.
250 One beep indicates apogee continuity, two beeps indicate
251 main continuity, three beeps indicate both apogee and main continuity,
252 and one longer "brap" sound indicates no continuity. For a dual
253 deploy flight, make sure you're getting three beeps before launching!
254 For apogee-only or motor eject flights, do what makes sense.
257 In idle mode, you will hear an audible "di-dit" ("I" for idle), and
258 the normal flight state machine is disengaged, thus
259 no ejection charges will fire. TeleMetrum also listens on the RF
260 link when in idle mode for packet mode requests sent from TeleDongle.
261 Commands can be issued to a TeleMetrum in idle mode over either
262 USB or the RF link equivalently.
263 Idle mode is useful for configuring TeleMetrum, for extracting data
264 from the on-board storage chip after flight, and for ground testing
268 One "neat trick" of particular value when TeleMetrum is used with very
269 large airframes, is that you can power the board up while the rocket
270 is horizontal, such that it comes up in idle mode. Then you can
271 raise the airframe to launch position, use a TeleDongle to open
272 a packet connection, and issue a 'reset' command which will cause
273 TeleMetrum to reboot, realize it's now nose-up, and thus choose
274 flight mode. This is much safer than standing on the top step of a
275 rickety step-ladder or hanging off the side of a launch tower with
276 a screw-driver trying to turn on your avionics before installing
283 TeleMetrum includes a complete GPS receiver. See a later section for
284 a brief explanation of how GPS works that will help you understand
285 the information in the telemetry stream. The bottom line is that
286 the TeleMetrum GPS receiver needs to lock onto at least four
287 satellites to obtain a solid 3 dimensional position fix and know
291 TeleMetrum provides backup power to the GPS chip any time a LiPo
292 battery is connected. This allows the receiver to "warm start" on
293 the launch rail much faster than if every power-on were a "cold start"
294 for the GPS receiver. In typical operations, powering up TeleMetrum
295 on the flight line in idle mode while performing final airframe
296 preparation will be sufficient to allow the GPS receiver to cold
297 start and acquire lock. Then the board can be powered down during
298 RSO review and installation on a launch rod or rail. When the board
299 is turned back on, the GPS system should lock very quickly, typically
300 long before igniter installation and return to the flight line are
305 <title>Ground Testing </title>
307 An important aspect of preparing a rocket using electronic deployment
308 for flight is ground testing the recovery system. Thanks
309 to the bi-directional RF link central to the Altus Metrum system,
310 this can be accomplished in a TeleMetrum-equipped rocket without as
311 much work as you may be accustomed to with other systems. It can
315 Just prep the rocket for flight, then power up TeleMetrum while the
316 airframe is horizontal. This will cause the firmware to go into
317 "idle" mode, in which the normal flight state machine is disabled and
318 charges will not fire without manual command. Then, establish an
319 RF packet connection from a TeleDongle-equipped computer using the
320 P command from a safe distance. You can now command TeleMetrum to
321 fire the apogee or main charges to complete your testing.
324 In order to reduce the chance of accidental firing of pyrotechnic
325 charges, the command to fire a charge is intentionally somewhat
326 difficult to type, and the built-in help is slightly cryptic to
327 prevent accidental echoing of characters from the help text back at
328 the board from firing a charge. The command to fire the apogee
329 drogue charge is 'i DoIt drogue' and the command to fire the main
330 charge is 'i DoIt main'.
334 <title>Radio Link </title>
336 The chip our boards are based on incorporates an RF transceiver, but
337 it's not a full duplex system... each end can only be transmitting or
338 receiving at any given moment. So we had to decide how to manage the
342 By design, TeleMetrum firmware listens for an RF connection when
343 it's in "idle mode" (turned on while the rocket is horizontal), which
344 allows us to use the RF link to configure the rocket, do things like
345 ejection tests, and extract data after a flight without having to
346 crack open the airframe. However, when the board is in "flight
347 mode" (turned on when the rocket is vertical) the TeleMetrum only
348 transmits and doesn't listen at all. That's because we want to put
349 ultimate priority on event detection and getting telemetry out of
350 the rocket and out over
351 the RF link in case the rocket crashes and we aren't able to extract
355 We don't use a 'normal packet radio' mode because they're just too
356 inefficient. The GFSK modulation we use is just FSK with the
357 baseband pulses passed through a
358 Gaussian filter before they go into the modulator to limit the
359 transmitted bandwidth. When combined with the hardware forward error
360 correction support in the cc1111 chip, this allows us to have a very
361 robust 38.4 kilobit data link with only 10 milliwatts of transmit power,
362 a whip antenna in the rocket, and a hand-held Yagi on the ground. We've
363 had a test flight above 12k AGL with good reception, and calculations
364 suggest we should be good to 40k AGL or more with a 5-element yagi on
365 the ground. We hope to fly boards to higher altitudes soon, and would
366 of course appreciate customer feedback on performance in higher
371 <title>Configurable Parameters</title>
373 Configuring a TeleMetrum board for flight is very simple. Because we
374 have both acceleration and pressure sensors, there is no need to set
375 a "mach delay", for example. The few configurable parameters can all
376 be set using a simple terminal program over the USB port or RF link
380 <title>Radio Channel</title>
382 Our firmware supports 10 channels. The default channel 0 corresponds
383 to a center frequency of 434.550 Mhz, and channels are spaced every
384 100 khz. Thus, channel 1 is 434.650 Mhz, and channel 9 is 435.550 Mhz.
385 At any given launch, we highly recommend coordinating who will use
386 each channel and when to avoid interference. And of course, both
387 TeleMetrum and TeleDongle must be configured to the same channel to
388 successfully communicate with each other.
391 To set the radio channel, use the 'c r' command, like 'c r 3' to set
393 As with all 'c' sub-commands, follow this with a 'c w' to write the
394 change to the parameter block in the on-board DataFlash chip.
398 <title>Apogee Delay</title>
400 Apogee delay is the number of seconds after TeleMetrum detects flight
401 apogee that the drogue charge should be fired. In most cases, this
402 should be left at the default of 0. However, if you are flying
403 redundant electronics such as for an L3 certification, you may wish
404 to set one of your altimeters to a positive delay so that both
405 primary and backup pyrotechnic charges do not fire simultaneously.
408 To set the apogee delay, use the [FIXME] command.
409 As with all 'c' sub-commands, follow this with a 'c w' to write the
410 change to the parameter block in the on-board DataFlash chip.
414 <title>Main Deployment Altitude</title>
416 By default, TeleMetrum will fire the main deployment charge at an
417 elevation of 250 meters (about 820 feet) above ground. We think this
418 is a good elevation for most airframes, but feel free to change this
419 to suit. In particular, if you are flying two altimeters, you may
421 deployment elevation for the backup altimeter to be something lower
422 than the primary so that both pyrotechnic charges don't fire
426 To set the main deployment altitude, use the [FIXME] command.
427 As with all 'c' sub-commands, follow this with a 'c w' to write the
428 change to the parameter block in the on-board DataFlash chip.
433 <title>Calibration</title>
435 There are only two calibrations required for a TeleMetrum board, and
436 only one for TeleDongle.
439 <title>Radio Frequency</title>
441 The radio frequency is synthesized from a clock based on the 48 Mhz
442 crystal on the board. The actual frequency of this oscillator must be
443 measured to generate a calibration constant. While our GFSK modulation
444 bandwidth is wide enough to allow boards to communicate even when
445 their oscillators are not on exactly the same frequency, performance
446 is best when they are closely matched.
447 Radio frequency calibration requires a calibrated frequency counter.
448 Fortunately, once set, the variation in frequency due to aging and
449 temperature changes is small enough that re-calibration by customers
450 should generally not be required.
453 To calibrate the radio frequency, connect the UHF antenna port to a
454 frequency counter, set the board to channel 0, and use the 'C'
455 command to generate a CW carrier. Wait for the transmitter temperature
456 to stabilize and the frequency to settle down.
457 Then, divide 434.550 Mhz by the
458 measured frequency and multiply by the current radio cal value show
459 in the 'c s' command. For an unprogrammed board, the default value
460 is 1186611. Take the resulting integer and program it using the 'c f'
461 command. Testing with the 'C' command again should show a carrier
462 within a few tens of Hertz of the intended frequency.
463 As with all 'c' sub-commands, follow this with a 'c w' to write the
464 change to the parameter block in the on-board DataFlash chip.
468 <title>Accelerometer</title>
470 The accelerometer we use has its own 5 volt power supply and
471 the output must be passed through a resistive voltage divider to match
472 the input of our 3.3 volt ADC. This means that unlike the barometric
473 sensor, the output of the acceleration sensor is not ratiometric to
474 the ADC converter, and calibration is required. We also support the
475 use of any of several accelerometers from a Freescale family that
476 includes at least +/- 40g, 50g, 100g, and 200g parts. Using gravity,
477 a simple 2-point calibration yields acceptable results capturing both
478 the different sensitivities and ranges of the different accelerometer
479 parts and any variation in power supply voltages or resistor values
480 in the divider network.
483 To calibrate the acceleration sensor, use the 'c a 0' command. You
484 will be prompted to orient the board vertically with the UHF antenna
485 up and press a key, then to orient the board vertically with the
486 UHF antenna down and press a key.
487 As with all 'c' sub-commands, follow this with a 'c w' to write the
488 change to the parameter block in the on-board DataFlash chip.
491 The +1g and -1g calibration points are included in each telemetry
492 frame and are part of the header extracted by ao-dumplog after flight.
493 Note that we always store and return raw ADC samples for each
494 sensor... nothing is permanently "lost" or "damaged" if the
501 <title>Using Altus Metrum Products</title>
503 <title>Being Legal</title>
505 First off, in the US, you need an [amateur radio license](../Radio) or
506 other authorization to legally operate the radio transmitters that are part
510 <title>In the Rocket</title>
512 In the rocket itself, you just need a [TeleMetrum](../TeleMetrum) board and
513 a LiPo rechargeable battery. An 860mAh battery weighs less than a 9V
514 alkaline battery, and will run a [TeleMetrum](../TeleMetrum) for hours.
517 By default, we ship TeleMetrum with a simple wire antenna. If your
518 electronics bay or the airframe it resides within is made of carbon fiber,
519 which is opaque to RF signals, you may choose to have an SMA connector
520 installed so that you can run a coaxial cable to an antenna mounted
521 elsewhere in the rocket.
525 <title>On the Ground</title>
527 To receive the data stream from the rocket, you need an antenna and short
528 feedline connected to one of our [TeleDongle](../TeleDongle) units. The
529 TeleDongle in turn plugs directly into the USB port on a notebook
530 computer. Because TeleDongle looks like a simple serial port, your computer
531 does not require special device drivers... just plug it in.
534 Right now, all of our application software is written for Linux. However,
535 because we understand that many people run Windows or MacOS, we are working
536 on a new ground station program written in Java that should work on all
540 After the flight, you can use the RF link to extract the more detailed data
541 logged in the rocket, or you can use a mini USB cable to plug into the
542 TeleMetrum board directly. Pulling out the data without having to open up
543 the rocket is pretty cool! A USB cable is also how you charge the LiPo
544 battery, so you'll want one of those anyway... the same cable used by lots
545 of digital cameras and other modern electronic stuff will work fine.
548 If your rocket lands out of sight, you may enjoy having a hand-held GPS
549 receiver, so that you can put in a waypoint for the last reported rocket
550 position before touch-down. This makes looking for your rocket a lot like
551 Geo-Cacheing... just go to the waypoint and look around starting from there.
554 You may also enjoy having a ham radio "HT" that covers the 70cm band... you
555 can use that with your antenna to direction-find the rocket on the ground
556 the same way you can use a Walston or Beeline tracker. This can be handy
557 if the rocket is hiding in sage brush or a tree, or if the last GPS position
558 doesn't get you close enough because the rocket dropped into a canyon, or
559 the wind is blowing it across a dry lake bed, or something like that... Keith
560 and Bdale both currently own and use the Yaesu VX-7R at launches.
563 So, to recap, on the ground the hardware you'll need includes:
564 <orderedlist inheritnum='inherit' numeration='arabic'>
566 an antenna and feedline
575 optionally, a handheld GPS receiver
578 optionally, an HT or receiver covering 435 Mhz
583 The best hand-held commercial directional antennas we've found for radio
584 direction finding rockets are from
585 <ulink url="http://www.arrowantennas.com/" >
588 The 440-3 and 440-5 are both good choices for finding a
589 TeleMetrum-equipped rocket when used with a suitable 70cm HT.
593 <title>Data Analysis</title>
595 Our software makes it easy to log the data from each flight, both the
596 telemetry received over the RF link during the flight itself, and the more
597 complete data log recorded in the DataFlash memory on the TeleMetrum
598 board. Once this data is on your computer, our postflight tools make it
599 easy to quickly get to the numbers everyone wants, like apogee altitude,
600 max acceleration, and max velocity. You can also generate and view a
601 standard set of plots showing the altitude, acceleration, and
602 velocity of the rocket during flight. And you can even export a data file
603 useable with Google Maps and Google Earth for visualizing the flight path
604 in two or three dimensions!
607 Our ultimate goal is to emit a set of files for each flight that can be
608 published as a web page per flight, or just viewed on your local disk with
613 <title>Future Plans</title>
615 In the future, we intend to offer "companion boards" for the rocket that will
616 plug in to TeleMetrum to collect additional data, provide more pyro channels,
617 and so forth. A reference design for a companion board will be documented
618 soon, and will be compatible with open source Arduino programming tools.
621 We are also working on the design of a hand-held ground terminal that will
622 allow monitoring the rocket's status, collecting data during flight, and
623 logging data after flight without the need for a notebook computer on the
624 flight line. Particularly since it is so difficult to read most notebook
625 screens in direct sunlight, we think this will be a great thing to have.
628 Because all of our work is open, both the hardware designs and the software,
629 if you have some great idea for an addition to the current Altus Metrum family,
630 feel free to dive in and help! Or let us know what you'd like to see that
631 we aren't already working on, and maybe we'll get excited about it too...