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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 extraordinary 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 e-matches
186 from companies like [insert company and product names for e-matches we've
187 tried and like] and with 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 by default 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 In flight mode, TeleMetrum turns on the GPS system, engages the flight
239 state machine, goes into transmit-only mode on the RF link sending
240 telemetry, and waits for launch to be detected. Flight mode is
241 indicated by an audible "di-dah-dah-dit" on the beeper, followed by
242 beeps indicating the state of the pyrotechnic igniter continuity.
243 One beep indicates [FIXME] apogee continuity, two beeps indicate
244 main continuity, three beeps indicate both apogee and main continuity,
245 and one longer "brap" sound indicates no continuity. For a dual
246 deploy flight, make sure you're getting three beeps before launching!
247 For apogee-only or motor eject flights, do what makes sense.
250 In idle mode, the normal flight state machine is disengaged, and thus
251 no ejection charges will fire. TeleMetrum also listens on the RF
252 link when in idle mode for packet mode requests sent from TeleDongle.
253 Commands can thus be issues to a TeleMetrum in idle mode over either
254 USB or the RF link equivalently.
255 Idle mode is useful for configuring TeleMetrum, for extracting data
256 from the on-board storage chip after flight, and for ground testing
260 One "neat trick" of particular value when TeleMetrum is used with very
261 large airframes, is that you can power the board up while the rocket
262 is horizontal, such that it comes up in idle mode. Then you can
263 raise the airframe to launch position, use a TeleDongle to open
264 a packet connection, and issue a 'reset' command which will cause
265 TeleMetrum to reboot, realize it's now nose-up, and thus choose
266 flight mode. This is much safer than standing on the top step of a
267 rickety step-ladder or hanging off the side of a launch tower with
268 a screw-driver trying to turn on your avionics before installing
275 TeleMetrum includes a complete GPS receiver. See a later section for
276 a brief explanation of how GPS works that will help you understand
277 the information in the telemetry stream. The bottom line is that
278 the TeleMetrum GPS receiver needs to lock onto at least four
279 satellites to obtain a solid 3 dimensional position fix and know
283 TeleMetrum provides backup power to the GPS chip any time a LiPo
284 battery is connected. This allows the receiver to "warm start" on
285 the launch rail much faster than if every power-on were a "cold start"
286 for the GPS receiver. In typical operations, powering up TeleMetrum
287 on the flight line in idle mode while performing final airframe
288 preparation will be sufficient to allow the GPS receiver to cold
289 start and acquire lock. Then the board can be powered down during
290 RSO review and installation on a launch rod or rail. When the board
291 is turned back on, the GPS system should lock very quickly, typically
292 long before igniter installation and return to the flight line are
297 <title>Ground Testing </title>
299 An important aspect of preparing a rocket using electronic deployment
300 for flight is ground testing the recovery system. Thanks
301 to the bi-directional RF link central to the Altus Metrum system,
302 this can be accomplished in a TeleMetrum-equipped rocket without as
303 much work as you may be accustomed to with other systems. It can
307 Just prep the rocket for flight, then power up TeleMetrum while the
308 airframe is horizontal. This will cause the firmware to go into
309 "idle" mode, in which the normal flight state machine is disabled and
310 charges will not fire without manual command. Then, establish an
311 RF packet connection from a TeleDongle-equipped computer using the
312 P command from a safe distance. You can now command TeleMetrum to
313 fire the apogee or main charges to complete your testing.
317 <title>Radio Link </title>
319 The chip our boards are based on incorporates an RF transceiver, but
320 it's not a full duplex system... each end can only be transmitting or
321 receiving at any given moment. So we have to decide how to manage the
325 By design, TeleMetrum firmware listens for an RF connection when
326 it's in "idle mode" (turned on while the rocket is horizontal), which
327 allows us to use the RF link to configure the rocket, do things like
328 ejection tests, and extract data after a flight without having to
329 crack open the airframe. However, when the board is in "flight
330 mode" (turned on when the rocket is vertical) the TeleMetrum only
331 transmits and doesn't listen at all. That's because we want to put
332 ultimate priority on event detection and getting telemetry out of
333 the rocket and out over
334 the RF link in case the rocket crashes and we aren't able to extract
338 We don't use a 'normal packet radio' mode because they're just too
339 inefficient. GFSK is just FSK with the baseband pulses passed through a
340 Gaussian filter before they go into the modulator to limit the
341 transmitted bandwidth. When combined with the hardware forward error
342 correction support in the cc1111 chip, this allows us to have a very
343 robust 38.4 kilobit data link with only 10 milliwatts of transmit power,
344 a whip antenna in the rocket, and a hand-held Yagi on the ground. We've
345 had a test flight above 12k AGL with good reception, and my calculations
346 say we should be good to 40k AGL or more with just a 5-element yagi on
347 the ground. I expect to push 30k with a 54mm minimum airframe I'm
348 working on now, so we'll hopefully have further practical confirmation
349 of our link margin in a few months.
357 <title>Using Altus Metrum Products</title>
359 <title>Being Legal</title>
361 First off, in the US, you need an [amateur radio license](../Radio) or
362 other authorization to legally operate the radio transmitters that are part
366 <title>In the Rocket</title>
368 In the rocket itself, you just need a [TeleMetrum](../TeleMetrum) board and
369 a LiPo rechargeable battery. An 860mAh battery weighs less than a 9V
370 alkaline battery, and will run a [TeleMetrum](../TeleMetrum) for hours.
373 By default, we ship TeleMetrum with a simple wire antenna. If your
374 electronics bay or the airframe it resides within is made of carbon fiber,
375 which is opaque to RF signals, you may choose to have an SMA connector
376 installed so that you can run a coaxial cable to an antenna mounted
377 elsewhere in the rocket.
381 <title>On the Ground</title>
383 To receive the data stream from the rocket, you need an antenna and short
384 feedline connected to one of our [TeleDongle](../TeleDongle) units. The
385 TeleDongle in turn plugs directly into the USB port on a notebook
386 computer. Because TeleDongle looks like a simple serial port, your computer
387 does not require special device drivers... just plug it in.
390 Right now, all of our application software is written for Linux. However,
391 because we understand that many people run Windows or MacOS, we are working
392 on a new ground station program written in Java that should work on all
396 After the flight, you can use the RF link to extract the more detailed data
397 logged in the rocket, or you can use a mini USB cable to plug into the
398 TeleMetrum board directly. Pulling out the data without having to open up
399 the rocket is pretty cool! A USB cable is also how you charge the LiPo
400 battery, so you'll want one of those anyway... the same cable used by lots
401 of digital cameras and other modern electronic stuff will work fine.
404 If your rocket lands out of sight, you may enjoy having a hand-held GPS
405 receiver, so that you can put in a waypoint for the last reported rocket
406 position before touch-down. This makes looking for your rocket a lot like
407 Geo-Cacheing... just go to the waypoint and look around starting from there.
410 You may also enjoy having a ham radio "HT" that covers the 70cm band... you
411 can use that with your antenna to direction-find the rocket on the ground
412 the same way you can use a Walston or Beeline tracker. This can be handy
413 if the rocket is hiding in sage brush or a tree, or if the last GPS position
414 doesn't get you close enough because the rocket dropped into a canyon, or
415 the wind is blowing it across a dry lake bed, or something like that... Keith
416 and Bdale both currently own and use the Yaesu VX-7R at launches.
419 So, to recap, on the ground the hardware you'll need includes:
420 <orderedlist inheritnum='inherit' numeration='arabic'>
422 an antenna and feedline
431 optionally, a handheld GPS receiver
434 optionally, an HT or receiver covering 435 Mhz
439 The best hand-held commercial directional antennas we've found for radio
440 direction finding rockets are from
441 <ulink url="http://www.arrowantennas.com/" >
444 The 440-3 and 440-5 are both good choices for finding a
445 TeleMetrum-equipped rocket when used with a suitable 70cm HT.
449 <title>Data Analysis</title>
451 Our software makes it easy to log the data from each flight, both the
452 telemetry received over the RF link during the flight itself, and the more
453 complete data log recorded in the DataFlash memory on the TeleMetrum
454 board. Once this data is on your computer, our postflight tools make it
455 easy to quickly get to the numbers everyone wants, like apogee altitude,
456 max acceleration, and max velocity. You can also generate and view a
457 standard set of plots showing the altitude, acceleration, and
458 velocity of the rocket during flight. And you can even export a data file
459 useable with Google Maps and Google Earth for visualizing the flight path
460 in two or three dimensions!
463 Our ultimate goal is to emit a set of files for each flight that can be
464 published as a web page per flight, or just viewed on your local disk with
469 <title>Future Plans</title>
471 In the future, we intend to offer "companion boards" for the rocket that will
472 plug in to TeleMetrum to collect additional data, provide more pyro channels,
473 and so forth. A reference design for a companion board will be documented
474 soon, and will be compatible with open source Arduino programming tools.
477 We are also working on the design of a hand-held ground terminal that will
478 allow monitoring the rocket's status, collecting data during flight, and
479 logging data after flight without the need for a notebook computer on the
480 flight line. Particularly since it is so difficult to read most notebook
481 screens in direct sunlight, we think this will be a great thing to have.
484 Because all of our work is open, both the hardware designs and the software,
485 if you have some great idea for an addition to the current Altus Metrum family,
486 feel free to dive in and help! Or let us know what you'd like to see that
487 we aren't already working on, and maybe we'll get excited about it too...