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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>Radio Link </title>
228 The chip our boards are based on incorporates an RF transceiver, but
229 it's not a full duplex system... each end can only be transmitting or
230 receiving at any given moment. So we have to decide how to manage the
234 By design, TeleMetrum firmware listens for an RF connection when
235 it's in "idle mode" (turned on while the rocket is horizontal), which
236 allows us to use the RF link to configure the rocket, do things like
237 ejection tests, and extract data after a flight without having to
238 crack open the airframe. However, when the board is in "flight
239 mode" (turned on when the rocket is vertical) the TeleMetrum only
240 transmits and doesn't listen at all. That's because we want to put
241 ultimate priority on event detection and getting telemetry out of
242 the rocket and out over
243 the RF link in case the rocket crashes and we aren't able to extract
247 We don't use a 'normal packet radio' mode because they're just too
248 inefficient. GFSK is just FSK with the baseband pulses passed through a
249 Gaussian filter before they go into the modulator to limit the
250 transmitted bandwidth. When combined with the hardware forward error
251 correction support in the cc1111 chip, this allows us to have a very
252 robust 38.4 kilobit data link with only 10 milliwatts of transmit power,
253 a whip antenna in the rocket, and a hand-held Yagi on the ground. We've
254 had a test flight above 12k AGL with good reception, and my calculations
255 say we should be good to 40k AGL or more with just a 5-element yagi on
256 the ground. I expect to push 30k with a 54mm minimum airframe I'm
257 working on now, so we'll hopefully have further practical confirmation
258 of our link margin in a few months.
266 <title>Using Altus Metrum Products</title>
268 <title>Being Legal</title>
270 First off, in the US, you need an [amateur radio license](../Radio) or
271 other authorization to legally operate the radio transmitters that are part
275 <title>In the Rocket</title>
277 In the rocket itself, you just need a [TeleMetrum](../TeleMetrum) board and
278 a LiPo rechargeable battery. An 860mAh battery weighs less than a 9V
279 alkaline battery, and will run a [TeleMetrum](../TeleMetrum) for hours.
282 By default, we ship TeleMetrum with a simple wire antenna. If your
283 electronics bay or the airframe it resides within is made of carbon fiber,
284 which is opaque to RF signals, you may choose to have an SMA connector
285 installed so that you can run a coaxial cable to an antenna mounted
286 elsewhere in the rocket.
290 <title>On the Ground</title>
292 To receive the data stream from the rocket, you need an antenna and short
293 feedline connected to one of our [TeleDongle](../TeleDongle) units. The
294 TeleDongle in turn plugs directly into the USB port on a notebook
295 computer. Because TeleDongle looks like a simple serial port, your computer
296 does not require special device drivers... just plug it in.
299 Right now, all of our application software is written for Linux. However,
300 because we understand that many people run Windows or MacOS, we are working
301 on a new ground station program written in Java that should work on all
305 After the flight, you can use the RF link to extract the more detailed data
306 logged in the rocket, or you can use a mini USB cable to plug into the
307 TeleMetrum board directly. Pulling out the data without having to open up
308 the rocket is pretty cool! A USB cable is also how you charge the LiPo
309 battery, so you'll want one of those anyway... the same cable used by lots
310 of digital cameras and other modern electronic stuff will work fine.
313 If your rocket lands out of sight, you may enjoy having a hand-held GPS
314 receiver, so that you can put in a waypoint for the last reported rocket
315 position before touch-down. This makes looking for your rocket a lot like
316 Geo-Cacheing... just go to the waypoint and look around starting from there.
319 You may also enjoy having a ham radio "HT" that covers the 70cm band... you
320 can use that with your antenna to direction-find the rocket on the ground
321 the same way you can use a Walston or Beeline tracker. This can be handy
322 if the rocket is hiding in sage brush or a tree, or if the last GPS position
323 doesn't get you close enough because the rocket dropped into a canyon, or
324 the wind is blowing it across a dry lake bed, or something like that... Keith
325 and Bdale both currently own and use the Yaesu VX-7R at launches.
328 So, to recap, on the ground the hardware you'll need includes:
329 <orderedlist inheritnum='inherit' numeration='arabic'>
331 an antenna and feedline
340 optionally, a handheld GPS receiver
343 optionally, an HT or receiver covering 435 Mhz
348 The best hand-held commercial directional antennas we've found for radio
349 direction finding rockets are from
350 <ulink url="http://www.arrowantennas.com/" >
353 The 440-3 and 440-5 are both good choices for finding a
354 TeleMetrum-equipped rocket when used with a suitable 70cm HT.
358 <title>Data Analysis</title>
360 Our software makes it easy to log the data from each flight, both the
361 telemetry received over the RF link during the flight itself, and the more
362 complete data log recorded in the DataFlash memory on the TeleMetrum
363 board. Once this data is on your computer, our postflight tools make it
364 easy to quickly get to the numbers everyone wants, like apogee altitude,
365 max acceleration, and max velocity. You can also generate and view a
366 standard set of plots showing the altitude, acceleration, and
367 velocity of the rocket during flight. And you can even export a data file
368 useable with Google Maps and Google Earth for visualizing the flight path
369 in two or three dimensions!
372 Our ultimate goal is to emit a set of files for each flight that can be
373 published as a web page per flight, or just viewed on your local disk with
378 <title>Future Plans</title>
380 In the future, we intend to offer "companion boards" for the rocket that will
381 plug in to TeleMetrum to collect additional data, provide more pyro channels,
382 and so forth. A reference design for a companion board will be documented
383 soon, and will be compatible with open source Arduino programming tools.
386 We are also working on the design of a hand-held ground terminal that will
387 allow monitoring the rocket's status, collecting data during flight, and
388 logging data after flight without the need for a notebook computer on the
389 flight line. Particularly since it is so difficult to read most notebook
390 screens in direct sunlight, we think this will be a great thing to have.
393 Because all of our work is open, both the hardware designs and the software,
394 if you have some great idea for an addition to the current Altus Metrum family,
395 feel free to dive in and help! Or let us know what you'd like to see that
396 we aren't already working on, and maybe we'll get excited about it too...