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5 <title>The Altus Metrum System</title>
6 <subtitle>An Owner's Manual for TeleMetrum, TeleMini and TeleDongle Devices</subtitle>
9 <firstname>Bdale</firstname>
10 <surname>Garbee</surname>
13 <firstname>Keith</firstname>
14 <surname>Packard</surname>
17 <firstname>Bob</firstname>
18 <surname>Finch</surname>
21 <firstname>Anthony</firstname>
22 <surname>Towns</surname>
26 <holder>Bdale Garbee and Keith Packard</holder>
30 This document is released under the terms of the
31 <ulink url="http://creativecommons.org/licenses/by-sa/3.0/">
32 Creative Commons ShareAlike 3.0
39 <revnumber>1.0</revnumber>
40 <date>24 August 2011</date>
42 Updated for software version 1.0. Note that 1.0 represents a
43 telemetry format change, meaning both ends of a link
44 (TeleMetrum/TeleMini and TeleDongle) must be updated or
45 communications will fail.
49 <revnumber>0.9</revnumber>
50 <date>18 January 2011</date>
52 Updated for software version 0.9. Note that 0.9 represents a
53 telemetry format change, meaning both ends of a link (TeleMetrum and
54 TeleDongle) must be updated or communications will fail.
58 <revnumber>0.8</revnumber>
59 <date>24 November 2010</date>
60 <revremark>Updated for software version 0.8 </revremark>
66 Thanks to Bob Finch, W9YA, NAR 12965, TRA 12350 for writing "The
67 Mere-Mortals Quick Start/Usage Guide to the Altus Metrum Starter
68 Kit" which formed the basis of the original Getting Started chapter
69 in this manual. Bob was one of our first customers for a production
70 TeleMetrum, and his continued enthusiasm and contributions
71 are immensely gratifying and highly appreciated!
74 And thanks to Anthony (AJ) Towns for major contributions including
75 the AltosUI graphing and site map code and associated documentation.
76 Free software means that our customers and friends can become our
77 collaborators, and we certainly appreciate this level of
81 Have fun using these products, and we hope to meet all of you
82 out on the rocket flight line somewhere.
85 NAR #87103, TRA #12201
88 NAR #88757, TRA #12200
93 <title>Introduction and Overview</title>
95 Welcome to the Altus Metrum community! Our circuits and software reflect
96 our passion for both hobby rocketry and Free Software. We hope their
97 capabilities and performance will delight you in every way, but by
98 releasing all of our hardware and software designs under open licenses,
99 we also hope to empower you to take as active a role in our collective
103 The first device created for our community was TeleMetrum, a dual
104 deploy altimeter with fully integrated GPS and radio telemetry
105 as standard features, and a "companion interface" that will
106 support optional capabilities in the future.
109 The newest device is TeleMini, a dual deploy altimeter with
110 radio telemetry and radio direction finding. This device is only
111 13mm by 38mm (½ inch by 1½ inches) and can fit easily in an 18mm
115 Complementing TeleMetrum and TeleMini is TeleDongle, a USB to RF
116 interface for communicating with the altimeters. Combined with your
117 choice of antenna and
118 notebook computer, TeleDongle and our associated user interface software
119 form a complete ground station capable of logging and displaying in-flight
120 telemetry, aiding rocket recovery, then processing and archiving flight
121 data for analysis and review.
124 More products will be added to the Altus Metrum family over time, and
125 we currently envision that this will be a single, comprehensive manual
126 for the entire product family.
130 <title>Getting Started</title>
132 The first thing to do after you check the inventory of parts in your
133 "starter kit" is to charge the battery.
136 The TeleMetrum battery can be charged by plugging it into the
137 corresponding socket of the TeleMetrum and then using the USB A to
139 cable to plug the TeleMetrum into your computer's USB socket. The
140 TeleMetrum circuitry will charge the battery whenever it is plugged
141 in, because the TeleMetrum's on-off switch does NOT control the
145 When the GPS chip is initially searching for
146 satellites, TeleMetrum will consume more current than it can pull
147 from the USB port, so the battery must be attached in order to get
148 satellite lock. Once GPS is locked, the current consumption goes back
149 down enough to enable charging while
150 running. So it's a good idea to fully charge the battery as your
151 first item of business so there is no issue getting and maintaining
152 satellite lock. The yellow charge indicator led will go out when the
153 battery is nearly full and the charger goes to trickle charge. It
154 can take several hours to fully recharge a deeply discharged battery.
157 The TeleMini battery can be charged by disconnecting it from the
158 TeleMini board and plugging it into a standalone battery charger
159 board, and connecting that via a USB cable to a laptop or other USB
163 The other active device in the starter kit is the TeleDongle USB to
164 RF interface. If you plug it in to your Mac or Linux computer it should
165 "just work", showing up as a serial port device. Windows systems need
166 driver information that is part of the AltOS download to know that the
167 existing USB modem driver will work. We therefore recommend installing
168 our software before plugging in TeleDongle if you are using a Windows
169 computer. If you are using Linux and are having problems, try moving
170 to a fresher kernel (2.6.33 or newer), as the USB serial driver had
171 ugly bugs in some earlier versions.
174 Next you should obtain and install the AltOS software. These include
175 the AltosUI ground station program, current firmware images for
176 TeleMetrum, TeleMini and TeleDongle, and a number of standalone
177 utilities that are rarely needed. Pre-built binary packages are
178 available for Linux, Microsoft Windows, and recent MacOSX versions.
179 Full source code and build instructions are also available.
180 The latest version may always be downloaded from
181 <ulink url="http://altusmetrum.org/AltOS"/>.
185 <title>Handling Precautions</title>
187 All Altus Metrum products are sophisticated electronic devices.
188 When handled gently and properly installed in an air-frame, they
189 will deliver impressive results. However, as with all electronic
190 devices, there are some precautions you must take.
193 The Lithium Polymer rechargeable batteries have an
194 extraordinary power density. This is great because we can fly with
195 much less battery mass than if we used alkaline batteries or previous
196 generation rechargeable batteries... but if they are punctured
197 or their leads are allowed to short, they can and will release their
199 Thus we recommend that you take some care when handling our batteries
200 and consider giving them some extra protection in your air-frame. We
201 often wrap them in suitable scraps of closed-cell packing foam before
202 strapping them down, for example.
205 The barometric sensors used on both TeleMetrum and TeleMini are
206 sensitive to sunlight. In normal TeleMetrum mounting situations, it
207 and all of the other surface mount components
208 are "down" towards whatever the underlying mounting surface is, so
209 this is not normally a problem. Please consider this, though, when
210 designing an installation, for example, in an air-frame with a
211 see-through plastic payload bay. It is particularly important to
212 consider this with TeleMini, both because the baro sensor is on the
213 "top" of the board, and because many model rockets with payload bays
214 use clear plastic for the payload bay! Replacing these with an opaque
215 cardboard tube, painting them, or wrapping them with a layer of masking
216 tape are all reasonable approaches to keep the sensor out of direct
220 The barometric sensor sampling port must be able to "breathe",
221 both by not being covered by foam or tape or other materials that might
222 directly block the hole on the top of the sensor, and also by having a
223 suitable static vent to outside air.
226 As with all other rocketry electronics, Altus Metrum altimeters must
227 be protected from exposure to corrosive motor exhaust and ejection
232 <title>Hardware Overview</title>
234 TeleMetrum is a 1 inch by 2.75 inch circuit board. It was designed to
235 fit inside coupler for 29mm air-frame tubing, but using it in a tube that
236 small in diameter may require some creativity in mounting and wiring
237 to succeed! The presence of an accelerometer means TeleMetrum should
238 be aligned along the flight axis of the airframe, and by default the 1/4
239 wave UHF wire antenna should be on the nose-cone end of the board. The
240 antenna wire is about 7 inches long, and wiring for a power switch and
241 the e-matches for apogee and main ejection charges depart from the
242 fin can end of the board, meaning an ideal "simple" avionics
243 bay for TeleMetrum should have at least 10 inches of interior length.
246 TeleMini is a 0.5 inch by 1.5 inch circuit board. It was designed to
247 fit inside an 18mm air-frame tube, but using it in a tube that
248 small in diameter may require some creativity in mounting and wiring
249 to succeed! Since there is no accelerometer, TeleMini can be mounted
250 in any convenient orientation. The default 1/4
251 wave UHF wire antenna attached to the center of one end of
252 the board is about 7 inches long, and wiring for a power switch and
253 the e-matches for apogee and main ejection charges depart from the
254 other end of the board, meaning an ideal "simple" avionics
255 bay for TeleMini should have at least 9 inches of interior length.
258 A typical TeleMetrum or TeleMini installation involves attaching
259 only a suitable Lithium Polymer battery, a single pole switch for
260 power on/off, and two pairs of wires connecting e-matches for the
261 apogee and main ejection charges.
264 By default, we use the unregulated output of the Li-Po battery directly
265 to fire ejection charges. This works marvelously with standard
266 low-current e-matches like the J-Tek from MJG Technologies, and with
267 Quest Q2G2 igniters. However, if you want or need to use a separate
268 pyro battery, check out the "External Pyro Battery" section in this
269 manual for instructions on how to wire that up. The altimeters are
270 designed to work with an external pyro battery of no more than 15 volts.
273 Ejection charges are wired directly to the screw terminal block
274 at the aft end of the altimeter. You'll need a very small straight
275 blade screwdriver for these screws, such as you might find in a
276 jeweler's screwdriver set.
279 TeleMetrum also uses the screw terminal block for the power
280 switch leads. On TeleMini, the power switch leads are soldered
281 directly to the board and can be connected directly to a switch.
284 For most air-frames, the integrated antennas are more than
285 adequate. However, if you are installing in a carbon-fiber or
286 metal electronics bay which is opaque to RF signals, you may need to
287 use off-board external antennas instead. In this case, you can
288 order an altimeter with an SMA connector for the UHF antenna
289 connection, and, on TeleMetrum, you can unplug the integrated GPS
290 antenna and select an appropriate off-board GPS antenna with
291 cable terminating in a U.FL connector.
295 <title>System Operation</title>
297 <title>Firmware Modes </title>
299 The AltOS firmware build for the altimeters has two
300 fundamental modes, "idle" and "flight". Which of these modes
301 the firmware operates in is determined at start up time. For
302 TeleMetrum, the mode is controlled by the orientation of the
303 rocket (well, actually the board, of course...) at the time
304 power is switched on. If the rocket is "nose up", then
305 TeleMetrum assumes it's on a rail or rod being prepared for
306 launch, so the firmware chooses flight mode. However, if the
307 rocket is more or less horizontal, the firmware instead enters
308 idle mode. Since TeleMini doesn't have an accelerometer we can
309 use to determine orientation, "idle" mode is selected when the
310 board receives a command packet within the first five seconds
311 of operation; if no packet is received, the board enters
315 At power on, you will hear three beeps or see three flashes
316 ("S" in Morse code for start up) and then a pause while
317 the altimeter completes initialization and self test, and decides
318 which mode to enter next.
321 In flight or "pad" mode, the altimeter engages the flight
322 state machine, goes into transmit-only mode to
323 send telemetry, and waits for launch to be detected.
324 Flight mode is indicated by an "di-dah-dah-dit" ("P" for pad)
325 on the beeper or lights, followed by beeps or flashes
326 indicating the state of the pyrotechnic igniter continuity.
327 One beep/flash indicates apogee continuity, two beeps/flashes
328 indicate main continuity, three beeps/flashes indicate both
329 apogee and main continuity, and one longer "brap" sound or
330 rapidly alternating lights indicates no continuity. For a
331 dual deploy flight, make sure you're getting three beeps or
332 flashes before launching! For apogee-only or motor eject
333 flights, do what makes sense.
336 If idle mode is entered, you will hear an audible "di-dit" or see
337 two short flashes ("I" for idle), and the flight state machine is
338 disengaged, thus no ejection charges will fire. The altimeters also
339 listen for the radio link when in idle mode for requests sent via
340 TeleDongle. Commands can be issued to a TeleMetrum in idle mode
342 USB or the radio link equivalently. TeleMini only has the radio link.
343 Idle mode is useful for configuring the altimeter, for extracting data
344 from the on-board storage chip after flight, and for ground testing
348 One "neat trick" of particular value when TeleMetrum is used with
349 very large air-frames, is that you can power the board up while the
350 rocket is horizontal, such that it comes up in idle mode. Then you can
351 raise the air-frame to launch position, and issue a 'reset' command
352 via TeleDongle over the radio link to cause the altimeter to reboot and
353 come up in flight mode. This is much safer than standing on the top
354 step of a rickety step-ladder or hanging off the side of a launch
355 tower with a screw-driver trying to turn on your avionics before
362 TeleMetrum includes a complete GPS receiver. A complete explanation
363 of how GPS works is beyond the scope of this manual, but the bottom
364 line is that the TeleMetrum GPS receiver needs to lock onto at least
365 four satellites to obtain a solid 3 dimensional position fix and know
369 TeleMetrum provides backup power to the GPS chip any time a
370 battery is connected. This allows the receiver to "warm start" on
371 the launch rail much faster than if every power-on were a GPS
372 "cold start". In typical operations, powering up TeleMetrum
373 on the flight line in idle mode while performing final air-frame
374 preparation will be sufficient to allow the GPS receiver to cold
375 start and acquire lock. Then the board can be powered down during
376 RSO review and installation on a launch rod or rail. When the board
377 is turned back on, the GPS system should lock very quickly, typically
378 long before igniter installation and return to the flight line are
383 <title>Controlling An Altimeter Over The Radio Link</title>
385 One of the unique features of the Altus Metrum system is
386 the ability to create a two way command link between TeleDongle
387 and an altimeter using the digital radio transceivers built into
388 each device. This allows you to interact with the altimeter from
389 afar, as if it were directly connected to the computer.
392 Any operation which can be performed with TeleMetrum can
393 either be done with TeleMetrum directly connected to the
394 computer via the USB cable, or through the radio
395 link. TeleMini doesn't provide a USB connector and so it is
396 always communicated with over radio. Select the appropriate
397 TeleDongle device when the list of devices is presented and
398 AltosUI will interact with an altimeter over the radio link.
401 One oddity in the current interface is how AltosUI selects the
402 frequency for radio communications. Instead of providing
403 an interface to specifically configure the frequency, it uses
404 whatever frequency was most recently selected for the target
405 TeleDongle device in Monitor Flight mode. If you haven't ever
406 used that mode with the TeleDongle in question, select the
407 Monitor Flight button from the top level UI, and pick the
408 appropriate TeleDongle device. Once the flight monitoring
409 window is open, select the desired frequency and then close it
410 down again. All radio communications will now use that frequency.
415 Save Flight Data—Recover flight data from the rocket without
421 Configure altimeter apogee delays or main deploy heights
422 to respond to changing launch conditions. You can also
423 'reboot' the altimeter. Use this to remotely enable the
424 flight computer by turning TeleMetrum on in "idle" mode,
425 then once the air-frame is oriented for launch, you can
426 reboot the altimeter and have it restart in pad mode
427 without having to climb the scary ladder.
432 Fire Igniters—Test your deployment charges without snaking
433 wires out through holes in the air-frame. Simply assembly the
434 rocket as if for flight with the apogee and main charges
435 loaded, then remotely command the altimeter to fire the
441 Operation over the radio link for configuring an altimeter, ground
442 testing igniters, and so forth uses the same RF frequencies as flight
443 telemetry. To configure the desired TeleDongle frequency, select
444 the monitor flight tab, then use the frequency selector and
445 close the window before performing other desired radio operations.
448 TeleMetrum only enables radio commanding in 'idle' mode, so
449 make sure you have TeleMetrum lying horizontally when you turn
450 it on. Otherwise, TeleMetrum will start in 'pad' mode ready for
451 flight, and will not be listening for command packets from TeleDongle.
454 TeleMini listens for a command packet for five seconds after
455 first being turned on, if it doesn't hear anything, it enters
456 'pad' mode, ready for flight and will no longer listen for
457 command packets. The easiest way to connect to TeleMini is to
458 initiate the command and select the TeleDongle device. At this
459 point, the TeleDongle will be attempting to communicate with
460 the TeleMini. Now turn TeleMini on, and it should immediately
461 start communicating with the TeleDongle and the desired
462 operation can be performed.
465 You can monitor the operation of the radio link by watching the
466 lights on the devices. The red LED will flash each time a packet
467 is tramsitted, while the green LED will light up on TeleDongle when
468 it is waiting to receive a packet from the altimeter.
472 <title>Ground Testing </title>
474 An important aspect of preparing a rocket using electronic deployment
475 for flight is ground testing the recovery system. Thanks
476 to the bi-directional radio link central to the Altus Metrum system,
477 this can be accomplished in a TeleMetrum or TeleMini equipped rocket
478 with less work than you may be accustomed to with other systems. It
482 Just prep the rocket for flight, then power up the altimeter
483 in "idle" mode (placing air-frame horizontal for TeleMetrum or
484 selected the Configure Altimeter tab for TeleMini). This will cause
485 the firmware to go into "idle" mode, in which the normal flight
486 state machine is disabled and charges will not fire without
487 manual command. You can now command the altimeter to fire the apogee
488 or main charges from a safe distance using your computer and
489 TeleDongle and the Fire Igniter tab to complete ejection testing.
493 <title>Radio Link </title>
495 The chip our boards are based on incorporates an RF transceiver, but
496 it's not a full duplex system... each end can only be transmitting or
497 receiving at any given moment. So we had to decide how to manage the
501 By design, the altimeter firmware listens for the radio link when
502 it's in "idle mode", which
503 allows us to use the radio link to configure the rocket, do things like
504 ejection tests, and extract data after a flight without having to
505 crack open the air-frame. However, when the board is in "flight
506 mode", the altimeter only
507 transmits and doesn't listen at all. That's because we want to put
508 ultimate priority on event detection and getting telemetry out of
510 the radio in case the rocket crashes and we aren't able to extract
514 We don't use a 'normal packet radio' mode like APRS because they're
515 just too inefficient. The GFSK modulation we use is FSK with the
516 base-band pulses passed through a
517 Gaussian filter before they go into the modulator to limit the
518 transmitted bandwidth. When combined with the hardware forward error
519 correction support in the cc1111 chip, this allows us to have a very
520 robust 38.4 kilobit data link with only 10 milliwatts of transmit
521 power, a whip antenna in the rocket, and a hand-held Yagi on the
522 ground. We've had flights to above 21k feet AGL with great reception,
523 and calculations suggest we should be good to well over 40k feet AGL
524 with a 5-element yagi on the ground. We hope to fly boards to higher
525 altitudes over time, and would of course appreciate customer feedback
526 on performance in higher altitude flights!
530 <title>Configurable Parameters</title>
532 Configuring an Altus Metrum altimeter for flight is very
533 simple. Even on our baro-only TeleMini board, the use of a Kalman
534 filter means there is no need to set a "mach delay". The few
535 configurable parameters can all be set using AltosUI over USB or
536 or radio link via TeleDongle.
539 <title>Radio Frequencies</title>
541 Altus Metrum boards support radio frequencies in the 70cm
542 band. By default, the configuration interface provides a
543 list of 10 "standard" frequencies in 100kHz channels starting at
544 434.550MHz. However, the firmware supports use of
545 any 50kHz multiple within the 70cm band. At any given
546 launch, we highly recommend coordinating when and by whom each
547 frequency will be used to avoid interference. And of course, both
548 altimeter and TeleDongle must be configured to the same
549 frequency to successfully communicate with each other.
552 To set the radio frequency, use the 'c R' command to specify the
553 radio transceiver configuration parameter. This parameter is computed
554 using the desired frequency, 'F', the radio calibration parameter, 'C' (showed by the 'c s' command) and
555 the standard calibration reference frequency, 'S', (normally 434.550MHz):
559 Round the result to the nearest integer value.
560 As with all 'c' sub-commands, follow this with a 'c w' to write the
561 change to the parameter block in the on-board flash on
562 your altimeter board if you want the change to stay in place across reboots.
566 <title>Apogee Delay</title>
568 Apogee delay is the number of seconds after the altimeter detects flight
569 apogee that the drogue charge should be fired. In most cases, this
570 should be left at the default of 0. However, if you are flying
571 redundant electronics such as for an L3 certification, you may wish
572 to set one of your altimeters to a positive delay so that both
573 primary and backup pyrotechnic charges do not fire simultaneously.
576 To set the apogee delay, use the 'c d' command.
577 As with all 'c' sub-commands, follow this with a 'c w' to write the
578 change to the parameter block in the on-board DataFlash chip.
581 Please note that the Altus Metrum apogee detection algorithm
582 fires exactly at apogee. If you are also flying an
583 altimeter like the PerfectFlite MAWD, which only supports
584 selecting 0 or 1 seconds of apogee delay, you may wish to
585 set the MAWD to 0 seconds delay and set the TeleMetrum to
586 fire your backup 2 or 3 seconds later to avoid any chance of
587 both charges firing simultaneously. We've flown several
588 air-frames this way quite happily, including Keith's
593 <title>Main Deployment Altitude</title>
595 By default, the altimeter will fire the main deployment charge at an
596 elevation of 250 meters (about 820 feet) above ground. We think this
597 is a good elevation for most air-frames, but feel free to change this
598 to suit. In particular, if you are flying two altimeters, you may
600 deployment elevation for the backup altimeter to be something lower
601 than the primary so that both pyrotechnic charges don't fire
605 To set the main deployment altitude, use the 'c m' command.
606 As with all 'c' sub-commands, follow this with a 'c w' to write the
607 change to the parameter block in the on-board DataFlash chip.
615 <title>AltosUI</title>
617 The AltosUI program provides a graphical user interface for
618 interacting with the Altus Metrum product family, including
619 TeleMetrum, TeleMini and TeleDongle. AltosUI can monitor telemetry data,
620 configure TeleMetrum, TeleMini and TeleDongle devices and many other
621 tasks. The primary interface window provides a selection of
622 buttons, one for each major activity in the system. This manual
623 is split into chapters, each of which documents one of the tasks
624 provided from the top-level toolbar.
627 <title>Monitor Flight</title>
628 <subtitle>Receive, Record and Display Telemetry Data</subtitle>
630 Selecting this item brings up a dialog box listing all of the
631 connected TeleDongle devices. When you choose one of these,
632 AltosUI will create a window to display telemetry data as
633 received by the selected TeleDongle device.
636 All telemetry data received are automatically recorded in
637 suitable log files. The name of the files includes the current
638 date and rocket serial and flight numbers.
641 The radio frequency being monitored by the TeleDongle device is
642 displayed at the top of the window. You can configure the
643 frequency by clicking on the frequency box and selecting the desired
644 frequency. AltosUI remembers the last frequency selected for each
645 TeleDongle and selects that automatically the next time you use
649 Below the TeleDongle frequency selector, the window contains a few
650 significant pieces of information about the altimeter providing
651 the telemetry data stream:
655 <para>The configured call-sign</para>
658 <para>The device serial number</para>
661 <para>The flight number. Each altimeter remembers how many
667 The rocket flight state. Each flight passes through several
668 states including Pad, Boost, Fast, Coast, Drogue, Main and
674 The Received Signal Strength Indicator value. This lets
675 you know how strong a signal TeleDongle is receiving. The
676 radio inside TeleDongle operates down to about -99dBm;
677 weaker signals may not be receivable. The packet link uses
678 error correction and detection techniques which prevent
679 incorrect data from being reported.
684 Finally, the largest portion of the window contains a set of
685 tabs, each of which contain some information about the rocket.
686 They're arranged in 'flight order' so that as the flight
687 progresses, the selected tab automatically switches to display
688 data relevant to the current state of the flight. You can select
689 other tabs at any time. The final 'table' tab contains all of
690 the telemetry data in one place.
693 <title>Launch Pad</title>
695 The 'Launch Pad' tab shows information used to decide when the
696 rocket is ready for flight. The first elements include red/green
697 indicators, if any of these is red, you'll want to evaluate
698 whether the rocket is ready to launch:
702 Battery Voltage. This indicates whether the Li-Po battery
703 powering the TeleMetrum has sufficient charge to last for
704 the duration of the flight. A value of more than
705 3.7V is required for a 'GO' status.
710 Apogee Igniter Voltage. This indicates whether the apogee
711 igniter has continuity. If the igniter has a low
712 resistance, then the voltage measured here will be close
713 to the Li-Po battery voltage. A value greater than 3.2V is
714 required for a 'GO' status.
719 Main Igniter Voltage. This indicates whether the main
720 igniter has continuity. If the igniter has a low
721 resistance, then the voltage measured here will be close
722 to the Li-Po battery voltage. A value greater than 3.2V is
723 required for a 'GO' status.
728 On-board Data Logging. This indicates whether there is
729 space remaining on-board to store flight data for the
730 upcoming flight. If you've downloaded data, but failed
731 to erase flights, there may not be any space
732 left. TeleMetrum can store multiple flights, depending
733 on the configured maximum flight log size. TeleMini
734 stores only a single flight, so it will need to be
735 downloaded and erased after each flight to capture
736 data. This only affects on-board flight logging; the
737 altimeter will still transmit telemetry and fire
738 ejection charges at the proper times.
743 GPS Locked. For a TeleMetrum device, this indicates whether the GPS receiver is
744 currently able to compute position information. GPS requires
745 at least 4 satellites to compute an accurate position.
750 GPS Ready. For a TeleMetrum device, this indicates whether GPS has reported at least
751 10 consecutive positions without losing lock. This ensures
752 that the GPS receiver has reliable reception from the
758 The Launchpad tab also shows the computed launch pad position
759 and altitude, averaging many reported positions to improve the
765 <title>Ascent</title>
767 This tab is shown during Boost, Fast and Coast
768 phases. The information displayed here helps monitor the
769 rocket as it heads towards apogee.
772 The height, speed and acceleration are shown along with the
773 maximum values for each of them. This allows you to quickly
774 answer the most commonly asked questions you'll hear during
778 The current latitude and longitude reported by the TeleMetrum GPS are
779 also shown. Note that under high acceleration, these values
780 may not get updated as the GPS receiver loses position
781 fix. Once the rocket starts coasting, the receiver should
782 start reporting position again.
785 Finally, the current igniter voltages are reported as in the
786 Launch Pad tab. This can help diagnose deployment failures
787 caused by wiring which comes loose under high acceleration.
791 <title>Descent</title>
793 Once the rocket has reached apogee and (we hope) activated the
794 apogee charge, attention switches to tracking the rocket on
795 the way back to the ground, and for dual-deploy flights,
796 waiting for the main charge to fire.
799 To monitor whether the apogee charge operated correctly, the
800 current descent rate is reported along with the current
801 height. Good descent rates generally range from 15-30m/s.
804 For TeleMetrum altimeters, you can locate the rocket in the sky
805 using the elevation and
806 bearing information to figure out where to look. Elevation is
807 in degrees above the horizon. Bearing is reported in degrees
808 relative to true north. Range can help figure out how big the
809 rocket will appear. Note that all of these values are relative
810 to the pad location. If the elevation is near 90°, the rocket
811 is over the pad, not over you.
814 Finally, the igniter voltages are reported in this tab as
815 well, both to monitor the main charge as well as to see what
816 the status of the apogee charge is.
820 <title>Landed</title>
822 Once the rocket is on the ground, attention switches to
823 recovery. While the radio signal is generally lost once the
824 rocket is on the ground, the last reported GPS position is
825 generally within a short distance of the actual landing location.
828 The last reported GPS position is reported both by
829 latitude and longitude as well as a bearing and distance from
830 the launch pad. The distance should give you a good idea of
831 whether you'll want to walk or hitch a ride. Take the reported
832 latitude and longitude and enter them into your hand-held GPS
833 unit and have that compute a track to the landing location.
836 Both TeleMini and TeleMetrum will continue to transmit RDF
837 tones after landing, allowing you to locate the rocket by
838 following the radio signal. You may need to get away from
839 the clutter of the flight line, or even get up on a hill (or
840 your neighbor's RV) to receive the RDF signal.
843 The maximum height, speed and acceleration reported
844 during the flight are displayed for your admiring observers.
847 To get more detailed information about the flight, you can
848 click on the 'Graph Flight' button which will bring up a
849 graph window for the current flight.
853 <title>Site Map</title>
855 When the TeleMetrum gets a GPS fix, the Site Map tab will map
856 the rocket's position to make it easier for you to locate the
857 rocket, both while it is in the air, and when it has landed. The
858 rocket's state is indicated by color: white for pad, red for
859 boost, pink for fast, yellow for coast, light blue for drogue,
860 dark blue for main, and black for landed.
863 The map's scale is approximately 3m (10ft) per pixel. The map
864 can be dragged using the left mouse button. The map will attempt
865 to keep the rocket roughly centered while data is being received.
868 Images are fetched automatically via the Google Maps Static API,
869 and are cached for reuse. If map images cannot be downloaded,
870 the rocket's path will be traced on a dark gray background
874 You can pre-load images for your favorite launch sites
875 before you leave home; check out the 'Preload Maps' section below.
880 <title>Save Flight Data</title>
882 The altimeter records flight data to its internal flash memory.
883 The TeleMetrum data is recorded at a much higher rate than the telemetry
884 system can handle, and is not subject to radio drop-outs. As
885 such, it provides a more complete and precise record of the
886 flight. The 'Save Flight Data' button allows you to read the
887 flash memory and write it to disk. As TeleMini has only a barometer, it
888 records data at the same rate as the telemetry signal, but there will be
889 no data lost due to telemetry drop-outs.
892 Clicking on the 'Save Flight Data' button brings up a list of
893 connected TeleMetrum and TeleDongle devices. If you select a
894 TeleMetrum device, the flight data will be downloaded from that
895 device directly. If you select a TeleDongle device, flight data
896 will be downloaded from a TeleMetrum or TeleMini device connected via the
897 packet command link to the specified TeleDongle. See the chapter
898 on Packet Command Mode for more information about this.
901 After the device has been selected, a dialog showing the
902 flight data saved in the device will be shown allowing you to
903 select which flights to download and which to delete. With
904 version 0.9 or newer firmware, you must erase flights in order
905 for the space they consume to be reused by another
906 flight. This prevents you from accidentally losing flight data
907 if you neglect to download data before flying again. Note that
908 if there is no more space available in the device, then no
909 data will be recorded for a flight.
912 The file name for each flight log is computed automatically
913 from the recorded flight date, altimeter serial number and
914 flight number information.
918 <title>Replay Flight</title>
920 Select this button and you are prompted to select a flight
921 record file, either a .telem file recording telemetry data or a
922 .eeprom file containing flight data saved from the altimeter
926 Once a flight record is selected, the flight monitor interface
927 is displayed and the flight is re-enacted in real time. Check
928 the Monitor Flight chapter above to learn how this window operates.
932 <title>Graph Data</title>
934 Select this button and you are prompted to select a flight
935 record file, either a .telem file recording telemetry data or a
936 .eeprom file containing flight data saved from
940 Once a flight record is selected, a window with two tabs is
941 opened. The first tab contains a graph with acceleration
942 (blue), velocity (green) and altitude (red) of the flight are
943 plotted and displayed, measured in metric units. The
944 apogee(yellow) and main(magenta) igniter voltages are also
945 displayed; high voltages indicate continuity, low voltages
946 indicate open circuits. The second tab contains some basic
950 The graph can be zoomed into a particular area by clicking and
951 dragging down and to the right. Once zoomed, the graph can be
952 reset by clicking and dragging up and to the left. Holding down
953 control and clicking and dragging allows the graph to be panned.
954 The right mouse button causes a pop-up menu to be displayed, giving
955 you the option save or print the plot.
958 Note that telemetry files will generally produce poor graphs
959 due to the lower sampling rate and missed telemetry packets.
960 Use saved flight data for graphing where possible.
964 <title>Export Data</title>
966 This tool takes the raw data files and makes them available for
967 external analysis. When you select this button, you are prompted to select a flight
968 data file (either .eeprom or .telem will do, remember that
969 .eeprom files contain higher resolution and more continuous
970 data). Next, a second dialog appears which is used to select
971 where to write the resulting file. It has a selector to choose
972 between CSV and KML file formats.
975 <title>Comma Separated Value Format</title>
977 This is a text file containing the data in a form suitable for
978 import into a spreadsheet or other external data analysis
979 tool. The first few lines of the file contain the version and
980 configuration information from the altimeter, then
981 there is a single header line which labels all of the
982 fields. All of these lines start with a '#' character which
983 most tools can be configured to skip over.
986 The remaining lines of the file contain the data, with each
987 field separated by a comma and at least one space. All of
988 the sensor values are converted to standard units, with the
989 barometric data reported in both pressure, altitude and
990 height above pad units.
994 <title>Keyhole Markup Language (for Google Earth)</title>
996 This is the format used by
997 Googleearth to provide an overlay within that
998 application. With this, you can use Googleearth to see the
999 whole flight path in 3D.
1004 <title>Configure Altimeter</title>
1006 Select this button and then select either a TeleMetrum or
1007 TeleDongle Device from the list provided. Selecting a TeleDongle
1008 device will use Packet Command Mode to configure a remote
1009 altimeter. Learn how to use this in the Packet Command
1013 The first few lines of the dialog provide information about the
1014 connected device, including the product name,
1015 software version and hardware serial number. Below that are the
1016 individual configuration entries.
1019 At the bottom of the dialog, there are four buttons:
1024 Save. This writes any changes to the
1025 configuration parameter block in flash memory. If you don't
1026 press this button, any changes you make will be lost.
1031 Reset. This resets the dialog to the most recently saved values,
1032 erasing any changes you have made.
1037 Reboot. This reboots the device. Use this to
1038 switch from idle to pad mode by rebooting once the rocket is
1039 oriented for flight.
1044 Close. This closes the dialog. Any unsaved changes will be
1050 The rest of the dialog contains the parameters to be configured.
1053 <title>Main Deploy Altitude</title>
1055 This sets the altitude (above the recorded pad altitude) at
1056 which the 'main' igniter will fire. The drop-down menu shows
1057 some common values, but you can edit the text directly and
1058 choose whatever you like. If the apogee charge fires below
1059 this altitude, then the main charge will fire two seconds
1060 after the apogee charge fires.
1064 <title>Apogee Delay</title>
1066 When flying redundant electronics, it's often important to
1067 ensure that multiple apogee charges don't fire at precisely
1068 the same time as that can over pressurize the apogee deployment
1069 bay and cause a structural failure of the air-frame. The Apogee
1070 Delay parameter tells the flight computer to fire the apogee
1071 charge a certain number of seconds after apogee has been
1076 <title>Radio Frequency</title>
1078 This configures which of the configured frequencies to use for both
1079 telemetry and packet command mode. Note that if you set this
1080 value via packet command mode, you will have to reconfigure
1081 the TeleDongle frequency before you will be able to use packet
1086 <title>Radio Calibration</title>
1088 The radios in every Altus Metrum device are calibrated at the
1089 factory to ensure that they transmit and receive on the
1090 specified frequency. You can adjust that
1091 calibration by changing this value. To change the TeleDongle's
1092 calibration, you must reprogram the unit completely.
1096 <title>Callsign</title>
1098 This sets the call sign included in each telemetry packet. Set this
1099 as needed to conform to your local radio regulations.
1103 <title>Maximum Flight Log Size</title>
1105 This sets the space (in kilobytes) allocated for each flight
1106 log. The available space will be divided into chunks of this
1107 size. A smaller value will allow more flights to be stored,
1108 a larger value will record data from longer flights.
1111 During ascent, TeleMetrum records barometer and
1112 accelerometer values 100 times per second, other analog
1113 information (voltages and temperature) 6 times per second
1114 and GPS data once per second. During descent, the non-GPS
1115 data is recorded 1/10th as often. Each barometer +
1116 accelerometer record takes 8 bytes.
1119 The default, 192kB, will store over 200 seconds of data at
1120 the ascent rate, or over 2000 seconds of data at the descent
1121 rate. That's plenty for most flights. This leaves enough
1122 storage for five flights in a 1MB system, or 10 flights in a
1126 The configuration block takes the last available block of
1127 memory, on v1.0 boards that's just 256 bytes. However, the
1128 flash part on the v1.1 boards uses 64kB for each block.
1131 TeleMini has 5kB of on-board storage, which is plenty for a
1132 single flight. Make sure you download and delete the data
1133 before a subsequent flight or it will not log any data.
1137 <title>Ignite Mode</title>
1139 TeleMetrum and TeleMini provide two igniter channels as they
1140 were originally designed as dual-deploy flight
1141 computers. This configuration parameter allows the two
1142 channels to be used in different configurations.
1147 Dual Deploy. This is the usual mode of operation; the
1148 'apogee' channel is fired at apogee and the 'main'
1149 channel at the height above ground specified by the
1150 'Main Deploy Altitude' during descent.
1155 Redundant Apogee. This fires both channels at
1156 apogee, the 'apogee' channel first followed after a two second
1157 delay by the 'main' channel.
1162 Redundant Main. This fires both channels at the
1163 height above ground specified by the Main Deploy
1164 Altitude setting during descent. The 'apogee'
1165 channel is fired first, followed after a two second
1166 delay by the 'main' channel.
1172 <title>Pad Orientation</title>
1174 Because it includes an accelerometer, TeleMetrum is
1175 sensitive to the orientation of the board. By default, it
1176 expects the antenna end to point forward. This parameter
1177 allows that default to be changed, permitting the board to
1178 be mounted with the antenna pointing aft instead.
1183 Antenna Up. In this mode, the antenna end of the
1184 TeleMetrum board must point forward, in line with the
1185 expected flight path.
1190 Antenna Down. In this mode, the antenna end of the
1191 TeleMetrum board must point aft, in line with the
1192 expected flight path.
1199 <title>Configure AltosUI</title>
1201 This button presents a dialog so that you can configure the AltosUI global settings.
1204 <title>Voice Settings</title>
1206 AltosUI provides voice announcements during flight so that you
1207 can keep your eyes on the sky and still get information about
1208 the current flight status. However, sometimes you don't want
1213 <para>Enable—turns all voice announcements on and off</para>
1217 Test Voice—Plays a short message allowing you to verify
1218 that the audio system is working and the volume settings
1225 <title>Log Directory</title>
1227 AltosUI logs all telemetry data and saves all TeleMetrum flash
1228 data to this directory. This directory is also used as the
1229 staring point when selecting data files for display or export.
1232 Click on the directory name to bring up a directory choosing
1233 dialog, select a new directory and click 'Select Directory' to
1234 change where AltosUI reads and writes data files.
1238 <title>Callsign</title>
1240 This value is transmitted in each command packet sent from
1241 TeleDongle and received from an altimeter. It is not used in
1242 telemetry mode, as the callsign configured in the altimeter board
1243 is included in all telemetry packets. Configure this
1244 with the AltosUI operators call sign as needed to comply with
1245 your local radio regulations.
1249 <title>Font Size</title>
1251 Selects the set of fonts used in the flight monitor
1252 window. Choose between the small, medium and large sets.
1256 <title>Serial Debug</title>
1258 This causes all communication with a connected device to be
1259 dumped to the console from which AltosUI was started. If
1260 you've started it from an icon or menu entry, the output
1261 will simply be discarded. This mode can be useful to debug
1262 various serial communication issues.
1266 <title>Manage Frequencies</title>
1268 This brings up a dialog where you can configure the set of
1269 frequencies shown in the various frequency menus. You can
1270 add as many as you like, or even reconfigure the default
1271 set. Changing this list does not affect the frequency
1272 settings of any devices, it only changes the set of
1273 frequencies shown in the menus.
1278 <title>Flash Image</title>
1280 This reprograms any Altus Metrum device by using a TeleMetrum
1281 or TeleDongle as a programming dongle. Please read the
1282 directions for flashing devices in the Updating Device
1283 Firmware chapter below.
1286 Once you have the programmer and target devices connected,
1287 push the 'Flash Image' button. That will present a dialog box
1288 listing all of the connected devices. Carefully select the
1289 programmer device, not the device to be programmed.
1292 Next, select the image to flash to the device. These are named
1293 with the product name and firmware version. The file selector
1294 will start in the directory containing the firmware included
1295 with the AltosUI package. Navigate to the directory containing
1296 the desired firmware if it isn't there.
1299 Next, a small dialog containing the device serial number and
1300 RF calibration values should appear. If these values are
1301 incorrect (possibly due to a corrupted image in the device),
1302 enter the correct values here.
1305 Finally, a dialog containing a progress bar will follow the
1306 programming process.
1309 When programming is complete, the target device will
1310 reboot. Note that if the target device is connected via USB, you
1311 will have to unplug it and then plug it back in for the USB
1312 connection to reset so that you can communicate with the device
1317 <title>Fire Igniter</title>
1319 This activates the igniter circuits in TeleMetrum to help test
1320 recovery systems deployment. Because this command can operate
1321 over the Packet Command Link, you can prepare the rocket as
1322 for flight and then test the recovery system without needing
1323 to snake wires inside the air-frame.
1326 Selecting the 'Fire Igniter' button brings up the usual device
1327 selection dialog. Pick the desired TeleDongle or TeleMetrum
1328 device. This brings up another window which shows the current
1329 continuity test status for both apogee and main charges.
1332 Next, select the desired igniter to fire. This will enable the
1336 Select the 'Arm' button. This enables the 'Fire' button. The
1337 word 'Arm' is replaced by a countdown timer indicating that
1338 you have 10 seconds to press the 'Fire' button or the system
1339 will deactivate, at which point you start over again at
1340 selecting the desired igniter.
1344 <title>Scan Channels</title>
1346 This listens for telemetry packets on all of the configured
1347 frequencies, displaying information about each device it
1348 receives a packet from. You can select which of the three
1349 telemetry formats should be tried; by default, it only listens
1350 for the standard telemetry packets used in v1.0 and later
1355 <title>Load Maps</title>
1357 Before heading out to a new launch site, you can use this to
1358 load satellite images in case you don't have internet
1359 connectivity at the site. This loads a fairly large area
1360 around the launch site, which should cover any flight you're likely to make.
1363 There's a drop-down menu of launch sites we know about; if
1364 your favorites aren't there, please let us know the lat/lon
1365 and name of the site. The contents of this list are actually
1366 downloaded at run-time, so as new sites are sent in, they'll
1367 get automatically added to this list.
1370 If the launch site isn't in the list, you can manually enter the lat/lon values
1373 Clicking the 'Load Map' button will fetch images from Google
1374 Maps; note that Google limits how many images you can fetch at
1375 once, so if you load more than one launch site, you may get
1376 some gray areas in the map which indicate that Google is tired
1377 of sending data to you. Try again later.
1381 <title>Monitor Idle</title>
1383 This brings up a dialog similar to the Monitor Flight UI,
1384 except it works with the altimeter in "idle" mode by sending
1385 query commands to discover the current state rather than
1386 listening for telemetry packets.
1391 <title>Using Altus Metrum Products</title>
1393 <title>Being Legal</title>
1395 First off, in the US, you need an <ulink url="http://www.altusmetrum.org/Radio/">amateur radio license</ulink> or
1396 other authorization to legally operate the radio transmitters that are part
1401 <title>In the Rocket</title>
1403 In the rocket itself, you just need a <ulink url="http://www.altusmetrum.org/TeleMetrum/">TeleMetrum</ulink> or
1404 <ulink url="http://www.altusmetrum.org/TeleMini/">TeleMini</ulink> board and
1405 a Li-Po rechargeable battery. An 860mAh battery weighs less than a 9V
1406 alkaline battery, and will run a TeleMetrum for hours.
1407 A 110mAh battery weighs less than a triple A battery and will run a TeleMetrum for
1408 a few hours, or a TeleMini for much (much) longer.
1411 By default, we ship the altimeters with a simple wire antenna. If your
1412 electronics bay or the air-frame it resides within is made of carbon fiber,
1413 which is opaque to RF signals, you may choose to have an SMA connector
1414 installed so that you can run a coaxial cable to an antenna mounted
1415 elsewhere in the rocket.
1419 <title>On the Ground</title>
1421 To receive the data stream from the rocket, you need an antenna and short
1422 feed-line connected to one of our <ulink url="http://www.altusmetrum.org/TeleDongle/">TeleDongle</ulink> units. The
1423 TeleDongle in turn plugs directly into the USB port on a notebook
1424 computer. Because TeleDongle looks like a simple serial port, your computer
1425 does not require special device drivers... just plug it in.
1428 The GUI tool, AltosUI, is written in Java and runs across
1429 Linux, Mac OS and Windows. There's also a suite of C tools
1430 for Linux which can perform most of the same tasks.
1433 After the flight, you can use the radio link to extract the more detailed data
1434 logged in either TeleMetrum or TeleMini devices, or you can use a mini USB cable to plug into the
1435 TeleMetrum board directly. Pulling out the data without having to open up
1436 the rocket is pretty cool! A USB cable is also how you charge the Li-Po
1437 battery, so you'll want one of those anyway... the same cable used by lots
1438 of digital cameras and other modern electronic stuff will work fine.
1441 If your TeleMetrum-equipped rocket lands out of sight, you may enjoy having a hand-held GPS
1442 receiver, so that you can put in a way-point for the last reported rocket
1443 position before touch-down. This makes looking for your rocket a lot like
1444 Geo-Caching... just go to the way-point and look around starting from there.
1447 You may also enjoy having a ham radio "HT" that covers the 70cm band... you
1448 can use that with your antenna to direction-find the rocket on the ground
1449 the same way you can use a Walston or Beeline tracker. This can be handy
1450 if the rocket is hiding in sage brush or a tree, or if the last GPS position
1451 doesn't get you close enough because the rocket dropped into a canyon, or
1452 the wind is blowing it across a dry lake bed, or something like that... Keith
1453 and Bdale both currently own and use the Yaesu VX-7R at launches.
1456 So, to recap, on the ground the hardware you'll need includes:
1457 <orderedlist inheritnum='inherit' numeration='arabic'>
1459 an antenna and feed-line
1468 optionally, a hand-held GPS receiver
1471 optionally, an HT or receiver covering 435 MHz
1476 The best hand-held commercial directional antennas we've found for radio
1477 direction finding rockets are from
1478 <ulink url="http://www.arrowantennas.com/" >
1481 The 440-3 and 440-5 are both good choices for finding a
1482 TeleMetrum- or TeleMini- equipped rocket when used with a suitable 70cm HT.
1486 <title>Data Analysis</title>
1488 Our software makes it easy to log the data from each flight, both the
1489 telemetry received during the flight itself, and the more
1490 complete data log recorded in the flash memory on the altimeter
1491 board. Once this data is on your computer, our post-flight tools make it
1492 easy to quickly get to the numbers everyone wants, like apogee altitude,
1493 max acceleration, and max velocity. You can also generate and view a
1494 standard set of plots showing the altitude, acceleration, and
1495 velocity of the rocket during flight. And you can even export a TeleMetrum data file
1496 usable with Google Maps and Google Earth for visualizing the flight path
1497 in two or three dimensions!
1500 Our ultimate goal is to emit a set of files for each flight that can be
1501 published as a web page per flight, or just viewed on your local disk with
1506 <title>Future Plans</title>
1508 In the future, we intend to offer "companion boards" for the rocket that will
1509 plug in to TeleMetrum to collect additional data, provide more pyro channels,
1510 and so forth. A reference design for a companion board will be documented
1511 soon, and will be compatible with open source Arduino programming tools.
1514 We are also working on the design of a hand-held ground terminal that will
1515 allow monitoring the rocket's status, collecting data during flight, and
1516 logging data after flight without the need for a notebook computer on the
1517 flight line. Particularly since it is so difficult to read most notebook
1518 screens in direct sunlight, we think this will be a great thing to have.
1521 Because all of our work is open, both the hardware designs and the software,
1522 if you have some great idea for an addition to the current Altus Metrum family,
1523 feel free to dive in and help! Or let us know what you'd like to see that
1524 we aren't already working on, and maybe we'll get excited about it too...
1529 <title>Altimeter Installation Recommendations</title>
1531 Building high-power rockets that fly safely is hard enough. Mix
1532 in some sophisticated electronics and a bunch of radio energy
1533 and oftentimes you find few perfect solutions. This chapter
1534 contains some suggestions about how to install Altus Metrum
1535 products into the rocket air-frame, including how to safely and
1536 reliably mix a variety of electronics into the same air-frame.
1539 <title>Mounting the Altimeter</title>
1541 The first consideration is to ensure that the altimeter is
1542 securely fastened to the air-frame. For TeleMetrum, we use
1543 nylon standoffs and nylon screws; they're good to at least 50G
1544 and cannot cause any electrical issues on the board. For
1545 TeleMini, we usually cut small pieces of 1/16" balsa to fit
1546 under the screw holes, and then take 2x56 nylon screws and
1547 screw them through the TeleMini mounting holes, through the
1548 balsa and into the underlying material.
1550 <orderedlist inheritnum='inherit' numeration='arabic'>
1552 Make sure TeleMetrum is aligned precisely along the axis of
1553 acceleration so that the accelerometer can accurately
1554 capture data during the flight.
1557 Watch for any metal touching components on the
1558 board. Shorting out connections on the bottom of the board
1559 can cause the altimeter to fail during flight.
1564 <title>Dealing with the Antenna</title>
1566 The antenna supplied is just a piece of solid, insulated,
1567 wire. If it gets damaged or broken, it can be easily
1568 replaced. It should be kept straight and not cut; bending or
1569 cutting it will change the resonant frequency and/or
1570 impedance, making it a less efficient radiator and thus
1571 reducing the range of the telemetry signal.
1574 Keeping metal away from the antenna will provide better range
1575 and a more even radiation pattern. In most rockets, it's not
1576 entirely possible to isolate the antenna from metal
1577 components; there are often bolts, all-thread and wires from other
1578 electronics to contend with. Just be aware that the more stuff
1579 like this around the antenna, the lower the range.
1582 Make sure the antenna is not inside a tube made or covered
1583 with conducting material. Carbon fiber is the most common
1584 culprit here -- CF is a good conductor and will effectively
1585 shield the antenna, dramatically reducing signal strength and
1586 range. Metallic flake paint is another effective shielding
1587 material which is to be avoided around any antennas.
1590 If the ebay is large enough, it can be convenient to simply
1591 mount the altimeter at one end and stretch the antenna out
1592 inside. Taping the antenna to the sled can keep it straight
1593 under acceleration. If there are metal rods, keep the
1594 antenna as far away as possible.
1597 For a shorter ebay, it's quite practical to have the antenna
1598 run through a bulkhead and into an adjacent bay. Drill a small
1599 hole in the bulkhead, pass the antenna wire through it and
1600 then seal it up with glue or clay. We've also used acrylic
1601 tubing to create a cavity for the antenna wire. This works a
1602 bit better in that the antenna is known to stay straight and
1603 not get folded by recovery components in the bay. Angle the
1604 tubing towards the side wall of the rocket and it ends up
1605 consuming very little space.
1608 If you need to place the antenna at a distance from the
1609 altimeter, you can replace the antenna with an edge-mounted
1610 SMA connector, and then run 50Ω coax from the board to the
1611 antenna. Building a remote antenna is beyond the scope of this
1616 <title>Preserving GPS Reception</title>
1618 The GPS antenna and receiver in TeleMetrum are highly
1619 sensitive and normally have no trouble tracking enough
1620 satellites to provide accurate position information for
1621 recovering the rocket. However, there are many ways to
1622 attenuate the GPS signal.
1623 <orderedlist inheritnum='inherit' numeration='arabic'>
1625 Conductive tubing or coatings. Carbon fiber and metal
1626 tubing, or metallic paint will all dramatically attenuate the
1627 GPS signal. We've never heard of anyone successfully
1628 receiving GPS from inside these materials.
1631 Metal components near the GPS patch antenna. These will
1632 de-tune the patch antenna, changing the resonant frequency
1633 away from the L1 carrier and reduce the effectiveness of the
1634 antenna. You can place as much stuff as you like beneath the
1635 antenna as that's covered with a ground plane. But, keep
1636 wires and metal out from above the patch antenna.
1642 <title>Radio Frequency Interference</title>
1644 Any altimeter will generate RFI; the digital circuits use
1645 high-frequency clocks that spray radio interference across a
1646 wide band. Altusmetrum altimeters generate intentional radio
1647 signals as well, increasing the amount of RF energy around the board.
1650 Rocketry altimeters also use precise sensors measuring air
1651 pressure and acceleration. Tiny changes in voltage can cause
1652 these sensor readings to vary by a huge amount. When the
1653 sensors start mis-reporting data, the altimeter can either
1654 fire the igniters at the wrong time, or not fire them at all.
1657 Voltages are induced when radio frequency energy is
1658 transmitted from one circuit to another. Here are things that
1659 increase the induced voltage and current:
1663 Keep wires from different circuits apart. Moving circuits
1664 further apart will reduce RFI.
1667 Avoid parallel wires from different circuits. The longer two
1668 wires run parallel to one another, the larger the amount of
1669 transferred energy. Cross wires at right angles to reduce
1673 Twist wires from the same circuits. Two wires the same
1674 distance from the transmitter will get the same amount of
1675 induced energy which will then cancel out. Any time you have
1676 a wire pair running together, twist the pair together to
1677 even out distances and reduce RFI. For altimeters, this
1678 includes battery leads, switch hookups and igniter
1682 Avoid resonant lengths. Know what frequencies are present
1683 in the environment and avoid having wire lengths near a
1684 natural resonant length. Altusmetrum products transmit on the
1685 70cm amateur band, so you should avoid lengths that are a
1686 simple ratio of that length; essentially any multiple of 1/4
1687 of the wavelength (17.5cm).
1692 <title>The Barometric Sensor</title>
1694 Altusmetrum altimeters measure altitude with a barometric
1695 sensor, essentially measuring the amount of air above the
1696 rocket to figure out how high it is. A large number of
1697 measurements are taken as the altimeter initializes itself to
1698 figure out the pad altitude. Subsequent measurements are then
1699 used to compute the height above the pad.
1702 To accurately measure atmospheric pressure, the ebay
1703 containing the altimeter must be vented outside the
1704 air-frame. The vent must be placed in a region of linear
1705 airflow, smooth and not in an area of increasing or decreasing
1709 The barometric sensor in the altimeter is quite sensitive to
1710 chemical damage from the products of APCP or BP combustion, so
1711 make sure the ebay is carefully sealed from any compartment
1712 which contains ejection charges or motors.
1716 <title>Ground Testing</title>
1718 The most important aspect of any installation is careful
1719 ground testing. Bringing an air-frame up to the LCO table which
1720 hasn't been ground tested can lead to delays or ejection
1721 charges firing on the pad, or, even worse, a recovery system
1725 Do a 'full systems' test that includes wiring up all igniters
1726 without any BP and turning on all of the electronics in flight
1727 mode. This will catch any mistakes in wiring and any residual
1728 RFI issues that might accidentally fire igniters at the wrong
1729 time. Let the air-frame sit for several minutes, checking for
1730 adequate telemetry signal strength and GPS lock.
1733 Ground test the ejection charges. Prepare the rocket for
1734 flight, loading ejection charges and igniters. Completely
1735 assemble the air-frame and then use the 'Fire Igniters'
1736 interface through a TeleDongle to command each charge to
1737 fire. Make sure the charge is sufficient to robustly separate
1738 the air-frame and deploy the recovery system.
1743 <title>Updating Device Firmware</title>
1745 The big conceptual thing to realize is that you have to use a
1746 TeleDongle as a programmer to update a TeleMetrum or TeleMini,
1747 and a TeleMetrum or other TeleDongle to program the TeleDongle
1748 Due to limited memory resources in the cc1111, we don't support
1749 programming directly over USB.
1752 You may wish to begin by ensuring you have current firmware images.
1753 These are distributed as part of the AltOS software bundle that
1754 also includes the AltosUI ground station program. Newer ground
1755 station versions typically work fine with older firmware versions,
1756 so you don't need to update your devices just to try out new
1757 software features. You can always download the most recent
1758 version from <ulink url="http://www.altusmetrum.org/AltOS/"/>.
1761 We recommend updating the altimeter first, before updating TeleDongle.
1764 <title>Updating TeleMetrum Firmware</title>
1765 <orderedlist inheritnum='inherit' numeration='arabic'>
1767 Find the 'programming cable' that you got as part of the starter
1768 kit, that has a red 8-pin MicroMaTch connector on one end and a
1769 red 4-pin MicroMaTch connector on the other end.
1772 Take the 2 screws out of the TeleDongle case to get access
1773 to the circuit board.
1776 Plug the 8-pin end of the programming cable to the
1777 matching connector on the TeleDongle, and the 4-pin end to the
1778 matching connector on the TeleMetrum.
1779 Note that each MicroMaTch connector has an alignment pin that
1780 goes through a hole in the PC board when you have the cable
1784 Attach a battery to the TeleMetrum board.
1787 Plug the TeleDongle into your computer's USB port, and power
1791 Run AltosUI, and select 'Flash Image' from the File menu.
1794 Pick the TeleDongle device from the list, identifying it as the
1798 Select the image you want put on the TeleMetrum, which should have a
1799 name in the form telemetrum-v1.1-1.0.0.ihx. It should be visible
1800 in the default directory, if not you may have to poke around
1801 your system to find it.
1804 Make sure the configuration parameters are reasonable
1805 looking. If the serial number and/or RF configuration
1806 values aren't right, you'll need to change them.
1809 Hit the 'OK' button and the software should proceed to flash
1810 the TeleMetrum with new firmware, showing a progress bar.
1813 Confirm that the TeleMetrum board seems to have updated OK, which you
1814 can do by plugging in to it over USB and using a terminal program
1815 to connect to the board and issue the 'v' command to check
1819 If something goes wrong, give it another try.
1824 <title>Updating TeleMini Firmware</title>
1825 <orderedlist inheritnum='inherit' numeration='arabic'>
1827 You'll need a special 'programming cable' to reprogram the
1828 TeleMini. It's available on the Altus Metrum web store, or
1829 you can make your own using an 8-pin MicroMaTch connector on
1830 one end and a set of four pins on the other.
1833 Take the 2 screws out of the TeleDongle case to get access
1834 to the circuit board.
1837 Plug the 8-pin end of the programming cable to the matching
1838 connector on the TeleDongle, and the 4-pins into the holes
1839 in the TeleMini circuit board. Note that the MicroMaTch
1840 connector has an alignment pin that goes through a hole in
1841 the PC board when you have the cable oriented correctly, and
1842 that pin 1 on the TeleMini board is marked with a square pad
1843 while the other pins have round pads.
1846 Attach a battery to the TeleMini board.
1849 Plug the TeleDongle into your computer's USB port, and power
1853 Run AltosUI, and select 'Flash Image' from the File menu.
1856 Pick the TeleDongle device from the list, identifying it as the
1860 Select the image you want put on the TeleMini, which should have a
1861 name in the form telemini-v1.0-1.0.0.ihx. It should be visible
1862 in the default directory, if not you may have to poke around
1863 your system to find it.
1866 Make sure the configuration parameters are reasonable
1867 looking. If the serial number and/or RF configuration
1868 values aren't right, you'll need to change them.
1871 Hit the 'OK' button and the software should proceed to flash
1872 the TeleMini with new firmware, showing a progress bar.
1875 Confirm that the TeleMini board seems to have updated OK, which you
1876 can do by configuring it over the radio link through the TeleDongle, or
1877 letting it come up in "flight" mode and listening for telemetry.
1880 If something goes wrong, give it another try.
1885 <title>Updating TeleDongle Firmware</title>
1887 Updating TeleDongle's firmware is just like updating TeleMetrum or TeleMini
1888 firmware, but you use either a TeleMetrum or another TeleDongle as the programmer.
1890 <orderedlist inheritnum='inherit' numeration='arabic'>
1892 Find the 'programming cable' that you got as part of the starter
1893 kit, that has a red 8-pin MicroMaTch connector on one end and a
1894 red 4-pin MicroMaTch connector on the other end.
1897 Find the USB cable that you got as part of the starter kit, and
1898 plug the "mini" end in to the mating connector on TeleMetrum or TeleDongle.
1901 Take the 2 screws out of the TeleDongle case to get access
1902 to the circuit board.
1905 Plug the 8-pin end of the programming cable to the
1906 matching connector on the programmer, and the 4-pin end to the
1907 matching connector on the TeleDongle.
1908 Note that each MicroMaTch connector has an alignment pin that
1909 goes through a hole in the PC board when you have the cable
1913 Attach a battery to the TeleMetrum board if you're using one.
1916 Plug both the programmer and the TeleDongle into your computer's USB
1917 ports, and power up the programmer.
1920 Run AltosUI, and select 'Flash Image' from the File menu.
1923 Pick the programmer device from the list, identifying it as the
1927 Select the image you want put on the TeleDongle, which should have a
1928 name in the form teledongle-v0.2-1.0.0.ihx. It should be visible
1929 in the default directory, if not you may have to poke around
1930 your system to find it.
1933 Make sure the configuration parameters are reasonable
1934 looking. If the serial number and/or RF configuration
1935 values aren't right, you'll need to change them. The TeleDongle
1936 serial number is on the "bottom" of the circuit board, and can
1937 usually be read through the translucent blue plastic case without
1938 needing to remove the board from the case.
1941 Hit the 'OK' button and the software should proceed to flash
1942 the TeleDongle with new firmware, showing a progress bar.
1945 Confirm that the TeleDongle board seems to have updated OK, which you
1946 can do by plugging in to it over USB and using a terminal program
1947 to connect to the board and issue the 'v' command to check
1948 the version, etc. Once you're happy, remove the programming cable
1949 and put the cover back on the TeleDongle.
1952 If something goes wrong, give it another try.
1956 Be careful removing the programming cable from the locking 8-pin
1957 connector on TeleMetrum. You'll need a fingernail or perhaps a thin
1958 screwdriver or knife blade to gently pry the locking ears out
1959 slightly to extract the connector. We used a locking connector on
1960 TeleMetrum to help ensure that the cabling to companion boards
1961 used in a rocket don't ever come loose accidentally in flight.
1966 <title>Hardware Specifications</title>
1968 <title>TeleMetrum Specifications</title>
1972 Recording altimeter for model rocketry.
1977 Supports dual deployment (can fire 2 ejection charges).
1982 70cm ham-band transceiver for telemetry down-link.
1987 Barometric pressure sensor good to 45k feet MSL.
1992 1-axis high-g accelerometer for motor characterization, capable of
1993 +/- 50g using default part.
1998 On-board, integrated GPS receiver with 5Hz update rate capability.
2003 On-board 1 megabyte non-volatile memory for flight data storage.
2008 USB interface for battery charging, configuration, and data recovery.
2013 Fully integrated support for Li-Po rechargeable batteries.
2018 Uses Li-Po to fire e-matches, can be modified to support
2019 optional separate pyro battery if needed.
2024 2.75 x 1 inch board designed to fit inside 29mm air-frame coupler tube.
2030 <title>TeleMini Specifications</title>
2034 Recording altimeter for model rocketry.
2039 Supports dual deployment (can fire 2 ejection charges).
2044 70cm ham-band transceiver for telemetry down-link.
2049 Barometric pressure sensor good to 45k feet MSL.
2054 On-board 5 kilobyte non-volatile memory for flight data storage.
2059 RF interface for battery charging, configuration, and data recovery.
2064 Support for Li-Po rechargeable batteries, using an external charger.
2069 Uses Li-Po to fire e-matches, can be modified to support
2070 optional separate pyro battery if needed.
2075 1.5 x .5 inch board designed to fit inside 18mm air-frame coupler tube.
2084 TeleMetrum seems to shut off when disconnected from the
2085 computer. Make sure the battery is adequately charged. Remember the
2086 unit will pull more power than the USB port can deliver before the
2087 GPS enters "locked" mode. The battery charges best when TeleMetrum
2091 It's impossible to stop the TeleDongle when it's in "p" mode, I have
2092 to unplug the USB cable? Make sure you have tried to "escape out" of
2093 this mode. If this doesn't work the reboot procedure for the
2094 TeleDongle *is* to simply unplug it. 'cu' however will retain it's
2095 outgoing buffer IF your "escape out" ('~~') does not work.
2096 At this point using either 'ao-view' (or possibly
2097 'cutemon') instead of 'cu' will 'clear' the issue and allow renewed
2101 The amber LED (on the TeleMetrum) lights up when both
2102 battery and USB are connected. Does this mean it's charging?
2103 Yes, the yellow LED indicates the charging at the 'regular' rate.
2104 If the led is out but the unit is still plugged into a USB port,
2105 then the battery is being charged at a 'trickle' rate.
2108 There are no "dit-dah-dah-dit" sound or lights like the manual mentions?
2109 That's the "pad" mode. Weak batteries might be the problem.
2110 It is also possible that the TeleMetrum is horizontal and the output
2111 is instead a "dit-dit" meaning 'idle'. For TeleMini, it's possible that
2112 it received a command packet which would have left it in "pad" mode.
2115 How do I save flight data?
2116 Live telemetry is written to file(s) whenever AltosUI is connected
2117 to the TeleDongle. The file area defaults to ~/TeleMetrum
2118 but is easily changed using the menus in AltosUI. The files that
2119 are written end in '.telem'. The after-flight
2120 data-dumped files will end in .eeprom and represent continuous data
2121 unlike the .telem files that are subject to losses
2122 along the RF data path.
2123 See the above instructions on what and how to save the eeprom stored
2124 data after physically retrieving your altimeter. Make sure to save
2125 the on-board data after each flight; while the TeleMetrum can store
2126 multiple flights, you never know when you'll lose the altimeter...
2130 <title>Notes for Older Software</title>
2133 Before AltosUI was written, using Altus Metrum devices required
2134 some finesse with the Linux command line. There was a limited
2135 GUI tool, ao-view, which provided functionality similar to the
2136 Monitor Flight window in AltosUI, but everything else was a
2137 fairly 80's experience. This appendix includes documentation for
2138 using that software.
2142 Both TeleMetrum and TeleDongle can be directly communicated
2143 with using USB ports. The first thing you should try after getting
2144 both units plugged into to your computer's USB port(s) is to run
2145 'ao-list' from a terminal-window to see what port-device-name each
2146 device has been assigned by the operating system.
2147 You will need this information to access the devices via their
2148 respective on-board firmware and data using other command line
2149 programs in the AltOS software suite.
2152 TeleMini can be communicated with through a TeleDongle device
2153 over the radio link. When first booted, TeleMini listens for a
2154 TeleDongle device and if it receives a packet, it goes into
2155 'idle' mode. Otherwise, it goes into 'pad' mode and waits to be
2156 launched. The easiest way to get it talking is to start the
2157 communication link on the TeleDongle and the power up the
2161 To access the device's firmware for configuration you need a terminal
2162 program such as you would use to talk to a modem. The software
2163 authors prefer using the program 'cu' which comes from the UUCP package
2164 on most Unix-like systems such as Linux. An example command line for
2165 cu might be 'cu -l /dev/ttyACM0', substituting the correct number
2166 indicated from running the
2167 ao-list program. Another reasonable terminal program for Linux is
2168 'cutecom'. The default 'escape'
2169 character used by CU (i.e. the character you use to
2170 issue commands to cu itself instead of sending the command as input
2171 to the connected device) is a '~'. You will need this for use in
2172 only two different ways during normal operations. First is to exit
2173 the program by sending a '~.' which is called a 'escape-disconnect'
2174 and allows you to close-out from 'cu'. The
2175 second use will be outlined later.
2178 All of the Altus Metrum devices share the concept of a two level
2179 command set in their firmware.
2180 The first layer has several single letter commands. Once
2181 you are using 'cu' (or 'cutecom') sending (typing) a '?'
2182 returns a full list of these
2183 commands. The second level are configuration sub-commands accessed
2184 using the 'c' command, for
2185 instance typing 'c?' will give you this second level of commands
2186 (all of which require the
2187 letter 'c' to access). Please note that most configuration options
2188 are stored only in Flash memory; TeleDongle doesn't provide any storage
2189 for these options and so they'll all be lost when you unplug it.
2192 Try setting these configuration ('c' or second level menu) values. A good
2193 place to start is by setting your call sign. By default, the boards
2194 use 'N0CALL' which is cute, but not exactly legal!
2195 Spend a few minutes getting comfortable with the units, their
2196 firmware, and 'cu' (or possibly 'cutecom').
2197 For instance, try to send
2198 (type) a 'c r 2' and verify the channel change by sending a 'c s'.
2199 Verify you can connect and disconnect from the units while in your
2200 terminal program by sending the escape-disconnect mentioned above.
2203 Note that the 'reboot' command, which is very useful on the altimeters,
2204 will likely just cause problems with the dongle. The *correct* way
2205 to reset the dongle is just to unplug and re-plug it.
2208 A fun thing to do at the launch site and something you can do while
2209 learning how to use these units is to play with the radio link access
2210 between an altimeter and the TeleDongle. Be aware that you *must* create
2211 some physical separation between the devices, otherwise the link will
2212 not function due to signal overload in the receivers in each device.
2215 Now might be a good time to take a break and read the rest of this
2216 manual, particularly about the two "modes" that the altimeters
2217 can be placed in. TeleMetrum uses the position of the device when booting
2218 up will determine whether the unit is in "pad" or "idle" mode. TeleMini
2219 enters "idle" mode when it receives a command packet within the first 5 seconds
2220 of being powered up, otherwise it enters "pad" mode.
2223 You can access an altimeter in idle mode from the TeleDongle's USB
2224 connection using the radio link
2225 by issuing a 'p' command to the TeleDongle. Practice connecting and
2226 disconnecting ('~~' while using 'cu') from the altimeter. If
2227 you cannot escape out of the "p" command, (by using a '~~' when in
2228 CU) then it is likely that your kernel has issues. Try a newer version.
2231 Using this radio link allows you to configure the altimeter, test
2232 fire e-matches and igniters from the flight line, check pyro-match
2233 continuity and so forth. You can leave the unit turned on while it
2234 is in 'idle mode' and then place the
2235 rocket vertically on the launch pad, walk away and then issue a
2236 reboot command. The altimeter will reboot and start sending data
2237 having changed to the "pad" mode. If the TeleDongle is not receiving
2238 this data, you can disconnect 'cu' from the TeleDongle using the
2239 procedures mentioned above and THEN connect to the TeleDongle from
2240 inside 'ao-view'. If this doesn't work, disconnect from the
2241 TeleDongle, unplug it, and try again after plugging it back in.
2244 In order to reduce the chance of accidental firing of pyrotechnic
2245 charges, the command to fire a charge is intentionally somewhat
2246 difficult to type, and the built-in help is slightly cryptic to
2247 prevent accidental echoing of characters from the help text back at
2248 the board from firing a charge. The command to fire the apogee
2249 drogue charge is 'i DoIt drogue' and the command to fire the main
2250 charge is 'i DoIt main'.
2253 On TeleMetrum, the GPS will eventually find enough satellites, lock in on them,
2254 and 'ao-view' will both auditorily announce and visually indicate
2256 Now you can launch knowing that you have a good data path and
2257 good satellite lock for flight data and recovery. Remember
2258 you MUST tell ao-view to connect to the TeleDongle explicitly in
2259 order for ao-view to be able to receive data.
2262 The altimeters provide RDF (radio direction finding) tones on
2263 the pad, during descent and after landing. These can be used to
2264 locate the rocket using a directional antenna; the signal
2265 strength providing an indication of the direction from receiver to rocket.
2268 TeleMetrum also provides GPS trekking data, which can further simplify
2269 locating the rocket once it has landed. (The last good GPS data
2270 received before touch-down will be on the data screen of 'ao-view'.)
2273 Once you have recovered the rocket you can download the eeprom
2274 contents using either 'ao-dumplog' (or possibly 'ao-eeprom'), over
2275 either a USB cable or over the radio link using TeleDongle.
2276 And by following the man page for 'ao-postflight' you can create
2277 various data output reports, graphs, and even KML data to see the
2278 flight trajectory in Google-earth. (Moving the viewing angle making
2279 sure to connect the yellow lines while in Google-earth is the proper
2283 As for ao-view.... some things are in the menu but don't do anything
2284 very useful. The developers have stopped working on ao-view to focus
2285 on a new, cross-platform ground station program. So ao-view may or
2286 may not be updated in the future. Mostly you just use
2287 the Log and Device menus. It has a wonderful display of the incoming
2288 flight data and I am sure you will enjoy what it has to say to you
2289 once you enable the voice output!
2293 <title>Calibration</title>
2295 There are only two calibrations required for a TeleMetrum board, and
2296 only one for TeleDongle and TeleMini. All boards are shipped from
2297 the factory pre-calibrated, but the procedures are documented here
2298 in case they are ever needed. Re-calibration is not supported by
2299 AltosUI, you must connect to the board with a serial terminal program
2300 and interact directly with the on-board command interpreter to effect
2304 <title>Radio Frequency</title>
2306 The radio frequency is synthesized from a clock based on the 48 MHz
2307 crystal on the board. The actual frequency of this oscillator
2308 must be measured to generate a calibration constant. While our
2310 bandwidth is wide enough to allow boards to communicate even when
2311 their oscillators are not on exactly the same frequency, performance
2312 is best when they are closely matched.
2313 Radio frequency calibration requires a calibrated frequency counter.
2314 Fortunately, once set, the variation in frequency due to aging and
2315 temperature changes is small enough that re-calibration by customers
2316 should generally not be required.
2319 To calibrate the radio frequency, connect the UHF antenna port to a
2320 frequency counter, set the board to 434.550MHz, and use the 'C'
2321 command in the on-board command interpreter to generate a CW
2322 carrier. For TeleMetrum, this is best done over USB. For TeleMini,
2323 note that the only way to escape the 'C' command is via power cycle
2324 since the board will no longer be listening for commands once it
2325 starts generating a CW carrier.
2328 Wait for the transmitter temperature to stabilize and the frequency
2329 to settle down. Then, divide 434.550 MHz by the
2330 measured frequency and multiply by the current radio cal value show
2331 in the 'c s' command. For an unprogrammed board, the default value
2332 is 1186611. Take the resulting integer and program it using the 'c f'
2333 command. Testing with the 'C' command again should show a carrier
2334 within a few tens of Hertz of the intended frequency.
2335 As with all 'c' sub-commands, follow this with a 'c w' to write the
2336 change to the parameter block in the on-board DataFlash chip.
2339 Note that any time you re-do the radio frequency calibration, the
2340 radio frequency is reset to the default 434.550 Mhz. If you want
2341 to use another frequency, you will have to set that again after
2342 calibration is completed.
2346 <title>TeleMetrum Accelerometer</title>
2348 The TeleMetrum accelerometer we use has its own 5 volt power
2350 the output must be passed through a resistive voltage divider to match
2351 the input of our 3.3 volt ADC. This means that unlike the barometric
2352 sensor, the output of the acceleration sensor is not ratio-metric to
2353 the ADC converter, and calibration is required. Explicitly
2354 calibrating the accelerometers also allows us to load any device
2355 from a Freescale family that includes at least +/- 40g, 50g, 100g,
2356 and 200g parts. Using gravity,
2357 a simple 2-point calibration yields acceptable results capturing both
2358 the different sensitivities and ranges of the different accelerometer
2359 parts and any variation in power supply voltages or resistor values
2360 in the divider network.
2363 To calibrate the acceleration sensor, use the 'c a 0' command. You
2364 will be prompted to orient the board vertically with the UHF antenna
2365 up and press a key, then to orient the board vertically with the
2366 UHF antenna down and press a key. Note that the accuracy of this
2367 calibration depends primarily on how perfectly vertical and still
2368 the board is held during the cal process. As with all 'c'
2369 sub-commands, follow this with a 'c w' to write the
2370 change to the parameter block in the on-board DataFlash chip.
2373 The +1g and -1g calibration points are included in each telemetry
2374 frame and are part of the header stored in onboard flash to be
2375 downloaded after flight. We always store and return raw ADC
2376 samples for each sensor... so nothing is permanently "lost" or
2377 "damaged" if the calibration is poor.
2380 In the unlikely event an accel cal goes badly, it is possible
2381 that TeleMetrum may always come up in 'pad mode' and as such not be
2382 listening to either the USB or radio link. If that happens,
2383 there is a special hook in the firmware to force the board back
2384 in to 'idle mode' so you can re-do the cal. To use this hook, you
2385 just need to ground the SPI clock pin at power-on. This pin is
2386 available as pin 2 on the 8-pin companion connector, and pin 1 is
2387 ground. So either carefully install a fine-gauge wire jumper
2388 between the two pins closest to the index hole end of the 8-pin
2389 connector, or plug in the programming cable to the 8-pin connector
2390 and use a small screwdriver or similar to short the two pins closest
2391 to the index post on the 4-pin end of the programming cable, and
2392 power up the board. It should come up in 'idle mode' (two beeps),
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