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2 <!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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5 <title>TeleMetrum</title>
6 <subtitle>Owner's Manual for the TeleMetrum System</subtitle>
9 <firstname>Bdale</firstname>
10 <surname>Garbee</surname>
13 <firstname>Keith</firstname>
14 <surname>Packard</surname>
18 <holder>Bdale Garbee and Keith Packard</holder>
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>Getting Started</title>
65 This chapter began as "The Mere-Mortals Quick Start/Usage Guide to
66 the Altus Metrum Starter Kit" by Bob Finch, W9YA, NAR 12965, TRA 12350,
67 w9ya@amsat.org. Bob was one of our first customers for a production
68 TeleMetrum, and the enthusiasm that led to his contribution of this
69 section is immensely gratifying and highy appreciated!
72 The first thing to do after you check the inventory of parts in your
73 "starter kit" is to charge the battery by plugging it into the
74 corresponding socket of the TeleMetrum and then using the USB A to B
75 cable to plug the Telemetrum into your computer's USB socket. The
76 TeleMetrum circuitry will charge the battery whenever it is plugged
77 into the usb socket. The TeleMetrum's on-off switch does NOT control
78 the charging circuitry. When the GPS chip is initially searching for
79 satellites, the unit will pull more current than it can pull from the
80 usb port, so the battery must be plugged in order to get a good
81 satellite lock. Once GPS is locked the current consumption goes back
82 down enough to enable charging while
83 running. So it's a good idea to fully charge the battery as your
84 first item of business so there is no issue getting and maintaining
85 satellite lock. The yellow charge indicator led will go out when the
86 battery is nearly full and the charger goes to trickle charge.
89 The other active device in the starter kit is the half-duplex TeleDongle
90 rf link. If you plug it in to your computer it should "just work",
91 showing up as a serial port device. If you are using Linux and are
92 having problems, try moving to a fresher kernel (2.6.33 or newer), as
93 there were some ugly USB serial driver bugs in earlier versions.
96 Next you should obtain and install the AltOS utilities. The first
97 generation sofware was written for Linux only. New software is coming
98 soon that will also run on Windows and Mac. For now, we'll concentrate
99 on Linux. If you are using Debian, an 'altos' package already exists,
100 see http://altusmetrum.org/AltOS for details on how to install it.
101 User-contributed directions for building packages on ArchLinux may be
102 found in the contrib/arch-linux directory as PKGBUILD files.
103 Between the debian/rules file and the PKGBUILD files in
104 contrib, you should find enough information to learn how to build the
105 software for any other version of Linux.
108 When you have successfully installed the software suite (either from
109 compiled source code or as the pre-built Debian package) you will
110 have 10 executable programs all of which have names beginning with 'ao-'.
111 ('ao-view' is the lone GUI-based program.
112 The rest are command-line based.) You will also
113 have 10 man pages, that give you basic info on each program.
114 And you will also get this documentation in two file types,
115 telemetrum.pdf and telemetrum.html.
116 Finally you will have a couple of control files that allow the ao-view
117 GUI-based program to appear in your menu of programs (under
118 the 'Internet' category).
121 Both Telemetrum and TeleDongle can be directly communicated
122 with using USB ports. The first thing you should try after getting
123 both units plugged into to your computer's usb port(s) is to run
124 'ao-list' from a terminal-window (I use konsole for this,) to see what
125 port-device-name each device has been assigned by the operating system.
126 You will need this information to access the devices via their
127 respective on-board firmware and data using other command line
128 programs in the AltOS software suite.
131 To access the device's firmware for configuration you need a terminal
132 program such as you would use to talk to a modem. The software
133 authors prefer using the program 'cu' which comes from the UUCP package
134 on most Unix-like systems such as Linux. An example command line for
135 cu might be 'cu -l /dev/ttyACM0', substituting the correct number
136 indicated from running the
137 ao-list program. Another reasonable terminal program for Linux is
138 'cutecom'. The default 'escape'
139 character used by CU (i.e. the character you use to
140 issue commands to cu itself instead of sending the command as input
141 to the connected device) is a '~'. You will need this for use in
142 only two different ways during normal operations. First is to exit
143 the program by sending a '~.' which is called a 'escape-disconnect'
144 and allows you to close-out from 'cu'. The
145 second use will be outlined later.
148 Both TeleMetrum and TeleDongle share the concept of a two level
150 firmware. The first layer has several single letter commands. Once
151 you are using 'cu' (or 'cutecom') sending (typing) a '?'
152 returns a full list of these
153 commands. The second level are configuration sub-commands accessed
154 using the 'c' command, for
155 instance typing 'c?' will give you this second level of commands
156 (all of which require the
157 letter 'c' to access). Please note that most configuration options
158 are stored only in DataFlash memory, and only TeleMetrum has this
159 memory to save the various values entered like the channel number
160 and your callsign when powered off. TeleDongle requires that you
161 set these each time you plug it in, which ao-view can help with.
164 Try setting these config ('c' or second level menu) values. A good
165 place to start is by setting your call sign. By default, the boards
166 use 'N0CALL' which is cute, but not exactly legal!
167 Spend a few minutes getting comfortable with the units, their
168 firmware, 'cu' (and possibly 'cutecom') For instance, try to send
169 (type) a 'cr2' and verify the channel change by sending a 'cs'.
170 Verify you can connect and disconnect from the units while in 'cu'
171 by sending the escape-disconnect mentioned above.
174 Note that the 'reboot' command, which is very useful on TeleMetrum,
175 will likely just cause problems with the dongle. The *correct* way
176 to reset the dongle is just to unplug and re-plug it.
179 A fun thing to do at the launch site and something you can do while
180 learning how to use these units is to play with the rf-link access
181 of the TeleMetrum from the TeleDongle. Be aware that you *must* create
182 some physical separation between the devices, otherwise the link will
183 not function due to signal overload in the receivers in each device.
186 Now might be a good time to take a break and read the rest of this
187 manual, particularly about the two "modes" that the TeleMetrum
188 can be placed in and how the position of the TeleMetrum when booting
189 up will determine whether the unit is in "pad" or "idle" mode.
192 You can access a TeleMetrum in idle mode from the Teledongle's USB
193 connection using the rf link
194 by issuing a 'p' command to the TeleDongle. Practice connecting and
195 disconnecting ('~~' while using 'cu') from the TeleMetrum. If
196 you cannot escape out of the "p" command, (by using a '~~' when in
197 CU) then it is likely that your kernel has issues. Try a newer version.
200 Using this rf link allows you to configure the TeleMetrum, test
201 fire e-matches and igniters from the flight line, check pyro-match
202 continuity and so forth. You can leave the unit turned on while it
203 is in 'idle mode' and then place the
204 rocket vertically on the launch pad, walk away and then issue a
205 reboot command. The TeleMetrum will reboot and start sending data
206 having changed to the "pad" mode. If the TeleDongle is not receiving
207 this data, you can disconnect 'cu' from the Teledongle using the
208 procedures mentioned above and THEN connect to the TeleDongle from
209 inside 'ao-view'. If this doesn't work, disconnect from the
210 TeleDongle, unplug it, and try again after plugging it back in.
213 Eventually the GPS will find enough satellites, lock in on them,
214 and 'ao-view' will both auditorially announce and visually indicate
216 Now you can launch knowing that you have a good data path and
217 good satellite lock for flight data and recovery. Remember
218 you MUST tell ao-view to connect to the TeleDongle explicitly in
219 order for ao-view to be able to receive data.
222 Both RDF (radio direction finding) tones from the TeleMetrum and
223 GPS trekking data are available and together are very useful in
224 locating the rocket once it has landed. (The last good GPS data
225 received before touch-down will be on the data screen of 'ao-view'.)
228 Once you have recovered the rocket you can download the eeprom
229 contents using either 'ao-dumplog' (or possibly 'ao-eeprom'), over
230 either a USB cable or over the radio link using TeleDongle.
231 And by following the man page for 'ao-postflight' you can create
232 various data output reports, graphs, and even kml data to see the
233 flight trajectory in google-earth. (Moving the viewing angle making
234 sure to connect the yellow lines while in google-earth is the proper
238 As for ao-view.... some things are in the menu but don't do anything
239 very useful. The developers have stopped working on ao-view to focus
240 on a new, cross-platform ground station program. Mostly you just use
241 the Log and Device menus. It has a wonderful display of the incoming
242 flight data and I am sure you will enjoy what it has to say to you
243 once you enable the voice output!
248 The altimeter (TeleMetrum) seems to shut off when disconnected from the
249 computer. Make sure the battery is adequately charged. Remember the
250 unit will pull more power than the USB port can deliver before the
251 GPS enters "locked" mode. The battery charges best when TeleMetrum
255 It's impossible to stop the TeleDongle when it's in "p" mode, I have
256 to unplug the USB cable? Make sure you have tried to "escape out" of
257 this mode. If this doesn't work the reboot procedure for the
258 TeleDongle *is* to simply unplug it. 'cu' however will retain it's
259 outgoing buffer IF your "escape out" ('~~') does not work.
260 At this point using either 'ao-view' (or possibly
261 'cutemon') instead of 'cu' will 'clear' the issue and allow renewed
265 The amber LED (on the TeleMetrum/altimeter) lights up when both
266 battery and USB are connected. Does this mean it's charging?
267 Yes, the yellow LED indicates the charging at the 'regular' rate.
268 If the led is out but the unit is still plugged into a USB port,
269 then the battery is being charged at a 'trickle' rate.
272 There are no "dit-dah-dah-dit" sound like the manual mentions?
273 That's the "pad" mode. Weak batteries might be the problem.
274 It is also possible that the unit is horizontal and the output
275 is instead a "dit-dit" meaning 'idle'.
278 It's unclear how to use 'ao-view' and other programs when 'cu'
279 is running. You cannot have more than one program connected to
280 the TeleDongle at one time without apparent data loss as the
281 incoming data will not make it to both programs intact.
282 Disconnect whatever programs aren't currently being used.
285 How do I save flight data?
286 Live telemetry is written to file(s) whenever 'ao-view' is connected
287 to the TeleDongle. The file area defaults to ~/altos
288 but is easily changed using the menus in 'ao-view'. The files that
289 are written end in '.telem'. The after-flight
290 data-dumped files will end in .eeprom and represent continuous data
291 unlike the rf-linked .telem files that are subject to the
292 turnarounds/data-packaging time slots in the half-duplex rf data path.
293 See the above instructions on what and how to save the eeprom stored
294 data after physically retrieving your TeleMetrum.
299 <title>Specifications</title>
303 Recording altimeter for model rocketry.
308 Supports dual deployment (can fire 2 ejection charges).
313 70cm ham-band transceiver for telemetry downlink.
318 Barometric pressure sensor good to 45k feet MSL.
323 1-axis high-g accelerometer for motor characterization, capable of
324 +/- 50g using default part.
329 On-board, integrated GPS receiver with 5hz update rate capability.
334 On-board 1 megabyte non-volatile memory for flight data storage.
339 USB interface for battery charging, configuration, and data recovery.
344 Fully integrated support for LiPo rechargeable batteries.
349 Uses LiPo to fire e-matches, support for optional separate pyro
355 2.75 x 1 inch board designed to fit inside 29mm airframe coupler tube.
361 <title>Handling Precautions</title>
363 TeleMetrum is a sophisticated electronic device. When handled gently and
364 properly installed in an airframe, it will deliver impressive results.
365 However, like all electronic devices, there are some precautions you
369 The Lithium Polymer rechargeable batteries used with TeleMetrum have an
370 extraordinary power density. This is great because we can fly with
371 much less battery mass than if we used alkaline batteries or previous
372 generation rechargeable batteries... but if they are punctured
373 or their leads are allowed to short, they can and will release their
375 Thus we recommend that you take some care when handling our batteries
376 and consider giving them some extra protection in your airframe. We
377 often wrap them in suitable scraps of closed-cell packing foam before
378 strapping them down, for example.
381 The TeleMetrum barometric sensor is sensitive to sunlight. In normal
382 mounting situations, it and all of the other surface mount components
383 are "down" towards whatever the underlying mounting surface is, so
384 this is not normally a problem. Please consider this, though, when
385 designing an installation, for example, in a 29mm airframe's see-through
389 The TeleMetrum barometric sensor sampling port must be able to "breathe",
390 both by not being covered by foam or tape or other materials that might
391 directly block the hole on the top of the sensor, but also by having a
392 suitable static vent to outside air.
395 As with all other rocketry electronics, TeleMetrum must be protected
396 from exposure to corrosive motor exhaust and ejection charge gasses.
400 <title>Hardware Overview</title>
402 TeleMetrum is a 1 inch by 2.75 inch circuit board. It was designed to
403 fit inside coupler for 29mm airframe tubing, but using it in a tube that
404 small in diameter may require some creativity in mounting and wiring
405 to succeed! The default 1/4
406 wave UHF wire antenna attached to the center of the nose-cone end of
407 the board is about 7 inches long, and wiring for a power switch and
408 the e-matches for apogee and main ejection charges depart from the
409 fin can end of the board. Given all this, an ideal "simple" avionics
410 bay for TeleMetrum should have at least 10 inches of interior length.
413 A typical TeleMetrum installation using the on-board GPS antenna and
414 default wire UHF antenna involves attaching only a suitable
415 Lithium Polymer battery, a single pole switch for power on/off, and
416 two pairs of wires connecting e-matches for the apogee and main ejection
420 By default, we use the unregulated output of the LiPo battery directly
421 to fire ejection charges. This works marvelously with standard
422 low-current e-matches like the J-Tek from MJG Technologies, and with
423 Quest Q2G2 igniters. However, if you
424 want or need to use a separate pyro battery, you can do so by adding
425 a second 2mm connector to position B2 on the board and cutting the
426 thick pcb trace connecting the LiPo battery to the pyro circuit between
427 the two silk screen marks on the surface mount side of the board shown
431 We offer two choices of pyro and power switch connector, or you can
432 choose neither and solder wires directly to the board. All three choices
433 are reasonable depending on the constraints of your airframe. Our
434 favorite option when there is sufficient room above the board is to use
435 the Tyco pin header with polarization and locking. If you choose this
436 option, you crimp individual wires for the power switch and e-matches
437 into a mating connector, and installing and removing the TeleMetrum
438 board from an airframe is as easy as plugging or unplugging two
439 connectors. If the airframe will not support this much height or if
440 you want to be able to directly attach e-match leads to the board, we
441 offer a screw terminal block. This is very similar to what most other
442 altimeter vendors provide and so may be the most familiar
443 option. You'll need a very small straight blade screwdriver to connect
444 and disconnect the board in this case, such as you might find in a
445 jeweler's screwdriver set. Finally, you can forego both options and
446 solder wires directly to the board, which may be the best choice for
447 minimum diameter and/or minimum mass designs.
450 For most airframes, the integrated GPS antenna and wire UHF antenna are
451 a great combination. However, if you are installing in a carbon-fiber
452 electronics bay which is opaque to RF signals, you may need to use
453 off-board external antennas instead. In this case, you can order
454 TeleMetrum with an SMA connector for the UHF antenna connection, and
455 you can unplug the integrated GPS antenna and select an appropriate
456 off-board GPS antenna with cable terminating in a U.FL connector.
460 <title>Operation</title>
462 <title>Firmware Modes </title>
464 The AltOS firmware build for TeleMetrum has two fundamental modes,
465 "idle" and "flight". Which of these modes the firmware operates in
466 is determined by the orientation of the rocket (well, actually the
467 board, of course...) at the time power is switched on. If the rocket
468 is "nose up", then TeleMetrum assumes it's on a rail or rod being
469 prepared for launch, so the firmware chooses flight mode. However,
470 if the rocket is more or less horizontal, the firmware instead enters
474 At power on, you will hear three beeps ("S" in Morse code for startup)
475 and then a pause while
476 TeleMetrum completes initialization and self tests, and decides which
480 In flight mode, TeleMetrum turns on the GPS system, engages the flight
481 state machine, goes into transmit-only mode on the RF link sending
482 telemetry, and waits for launch to be detected. Flight mode is
483 indicated by an audible "di-dah-dah-dit" ("P" for pad) on the
485 beeps indicating the state of the pyrotechnic igniter continuity.
486 One beep indicates apogee continuity, two beeps indicate
487 main continuity, three beeps indicate both apogee and main continuity,
488 and one longer "brap" sound indicates no continuity. For a dual
489 deploy flight, make sure you're getting three beeps before launching!
490 For apogee-only or motor eject flights, do what makes sense.
493 In idle mode, you will hear an audible "di-dit" ("I" for idle), and
494 the normal flight state machine is disengaged, thus
495 no ejection charges will fire. TeleMetrum also listens on the RF
496 link when in idle mode for packet mode requests sent from TeleDongle.
497 Commands can be issued to a TeleMetrum in idle mode over either
498 USB or the RF link equivalently.
499 Idle mode is useful for configuring TeleMetrum, for extracting data
500 from the on-board storage chip after flight, and for ground testing
504 One "neat trick" of particular value when TeleMetrum is used with very
505 large airframes, is that you can power the board up while the rocket
506 is horizontal, such that it comes up in idle mode. Then you can
507 raise the airframe to launch position, use a TeleDongle to open
508 a packet connection, and issue a 'reset' command which will cause
509 TeleMetrum to reboot, realize it's now nose-up, and thus choose
510 flight mode. This is much safer than standing on the top step of a
511 rickety step-ladder or hanging off the side of a launch tower with
512 a screw-driver trying to turn on your avionics before installing
519 TeleMetrum includes a complete GPS receiver. See a later section for
520 a brief explanation of how GPS works that will help you understand
521 the information in the telemetry stream. The bottom line is that
522 the TeleMetrum GPS receiver needs to lock onto at least four
523 satellites to obtain a solid 3 dimensional position fix and know
527 TeleMetrum provides backup power to the GPS chip any time a LiPo
528 battery is connected. This allows the receiver to "warm start" on
529 the launch rail much faster than if every power-on were a "cold start"
530 for the GPS receiver. In typical operations, powering up TeleMetrum
531 on the flight line in idle mode while performing final airframe
532 preparation will be sufficient to allow the GPS receiver to cold
533 start and acquire lock. Then the board can be powered down during
534 RSO review and installation on a launch rod or rail. When the board
535 is turned back on, the GPS system should lock very quickly, typically
536 long before igniter installation and return to the flight line are
541 <title>Ground Testing </title>
543 An important aspect of preparing a rocket using electronic deployment
544 for flight is ground testing the recovery system. Thanks
545 to the bi-directional RF link central to the Altus Metrum system,
546 this can be accomplished in a TeleMetrum-equipped rocket without as
547 much work as you may be accustomed to with other systems. It can
551 Just prep the rocket for flight, then power up TeleMetrum while the
552 airframe is horizontal. This will cause the firmware to go into
553 "idle" mode, in which the normal flight state machine is disabled and
554 charges will not fire without manual command. Then, establish an
555 RF packet connection from a TeleDongle-equipped computer using the
556 P command from a safe distance. You can now command TeleMetrum to
557 fire the apogee or main charges to complete your testing.
560 In order to reduce the chance of accidental firing of pyrotechnic
561 charges, the command to fire a charge is intentionally somewhat
562 difficult to type, and the built-in help is slightly cryptic to
563 prevent accidental echoing of characters from the help text back at
564 the board from firing a charge. The command to fire the apogee
565 drogue charge is 'i DoIt drogue' and the command to fire the main
566 charge is 'i DoIt main'.
570 <title>Radio Link </title>
572 The chip our boards are based on incorporates an RF transceiver, but
573 it's not a full duplex system... each end can only be transmitting or
574 receiving at any given moment. So we had to decide how to manage the
578 By design, TeleMetrum firmware listens for an RF connection when
579 it's in "idle mode" (turned on while the rocket is horizontal), which
580 allows us to use the RF link to configure the rocket, do things like
581 ejection tests, and extract data after a flight without having to
582 crack open the airframe. However, when the board is in "flight
583 mode" (turned on when the rocket is vertical) the TeleMetrum only
584 transmits and doesn't listen at all. That's because we want to put
585 ultimate priority on event detection and getting telemetry out of
586 the rocket and out over
587 the RF link in case the rocket crashes and we aren't able to extract
591 We don't use a 'normal packet radio' mode because they're just too
592 inefficient. The GFSK modulation we use is just FSK with the
593 baseband pulses passed through a
594 Gaussian filter before they go into the modulator to limit the
595 transmitted bandwidth. When combined with the hardware forward error
596 correction support in the cc1111 chip, this allows us to have a very
597 robust 38.4 kilobit data link with only 10 milliwatts of transmit power,
598 a whip antenna in the rocket, and a hand-held Yagi on the ground. We've
599 had a test flight above 12k AGL with good reception, and calculations
600 suggest we should be good to 40k AGL or more with a 5-element yagi on
601 the ground. We hope to fly boards to higher altitudes soon, and would
602 of course appreciate customer feedback on performance in higher
607 <title>Configurable Parameters</title>
609 Configuring a TeleMetrum board for flight is very simple. Because we
610 have both acceleration and pressure sensors, there is no need to set
611 a "mach delay", for example. The few configurable parameters can all
612 be set using a simple terminal program over the USB port or RF link
616 <title>Radio Channel</title>
618 Our firmware supports 10 channels. The default channel 0 corresponds
619 to a center frequency of 434.550 Mhz, and channels are spaced every
620 100 khz. Thus, channel 1 is 434.650 Mhz, and channel 9 is 435.550 Mhz.
621 At any given launch, we highly recommend coordinating who will use
622 each channel and when to avoid interference. And of course, both
623 TeleMetrum and TeleDongle must be configured to the same channel to
624 successfully communicate with each other.
627 To set the radio channel, use the 'c r' command, like 'c r 3' to set
629 As with all 'c' sub-commands, follow this with a 'c w' to write the
630 change to the parameter block in the on-board DataFlash chip.
634 <title>Apogee Delay</title>
636 Apogee delay is the number of seconds after TeleMetrum detects flight
637 apogee that the drogue charge should be fired. In most cases, this
638 should be left at the default of 0. However, if you are flying
639 redundant electronics such as for an L3 certification, you may wish
640 to set one of your altimeters to a positive delay so that both
641 primary and backup pyrotechnic charges do not fire simultaneously.
644 To set the apogee delay, use the [FIXME] command.
645 As with all 'c' sub-commands, follow this with a 'c w' to write the
646 change to the parameter block in the on-board DataFlash chip.
650 <title>Main Deployment Altitude</title>
652 By default, TeleMetrum will fire the main deployment charge at an
653 elevation of 250 meters (about 820 feet) above ground. We think this
654 is a good elevation for most airframes, but feel free to change this
655 to suit. In particular, if you are flying two altimeters, you may
657 deployment elevation for the backup altimeter to be something lower
658 than the primary so that both pyrotechnic charges don't fire
662 To set the main deployment altitude, use the [FIXME] command.
663 As with all 'c' sub-commands, follow this with a 'c w' to write the
664 change to the parameter block in the on-board DataFlash chip.
669 <title>Calibration</title>
671 There are only two calibrations required for a TeleMetrum board, and
672 only one for TeleDongle.
675 <title>Radio Frequency</title>
677 The radio frequency is synthesized from a clock based on the 48 Mhz
678 crystal on the board. The actual frequency of this oscillator must be
679 measured to generate a calibration constant. While our GFSK modulation
680 bandwidth is wide enough to allow boards to communicate even when
681 their oscillators are not on exactly the same frequency, performance
682 is best when they are closely matched.
683 Radio frequency calibration requires a calibrated frequency counter.
684 Fortunately, once set, the variation in frequency due to aging and
685 temperature changes is small enough that re-calibration by customers
686 should generally not be required.
689 To calibrate the radio frequency, connect the UHF antenna port to a
690 frequency counter, set the board to channel 0, and use the 'C'
691 command to generate a CW carrier. Wait for the transmitter temperature
692 to stabilize and the frequency to settle down.
693 Then, divide 434.550 Mhz by the
694 measured frequency and multiply by the current radio cal value show
695 in the 'c s' command. For an unprogrammed board, the default value
696 is 1186611. Take the resulting integer and program it using the 'c f'
697 command. Testing with the 'C' command again should show a carrier
698 within a few tens of Hertz of the intended frequency.
699 As with all 'c' sub-commands, follow this with a 'c w' to write the
700 change to the parameter block in the on-board DataFlash chip.
704 <title>Accelerometer</title>
706 The accelerometer we use has its own 5 volt power supply and
707 the output must be passed through a resistive voltage divider to match
708 the input of our 3.3 volt ADC. This means that unlike the barometric
709 sensor, the output of the acceleration sensor is not ratiometric to
710 the ADC converter, and calibration is required. We also support the
711 use of any of several accelerometers from a Freescale family that
712 includes at least +/- 40g, 50g, 100g, and 200g parts. Using gravity,
713 a simple 2-point calibration yields acceptable results capturing both
714 the different sensitivities and ranges of the different accelerometer
715 parts and any variation in power supply voltages or resistor values
716 in the divider network.
719 To calibrate the acceleration sensor, use the 'c a 0' command. You
720 will be prompted to orient the board vertically with the UHF antenna
721 up and press a key, then to orient the board vertically with the
722 UHF antenna down and press a key.
723 As with all 'c' sub-commands, follow this with a 'c w' to write the
724 change to the parameter block in the on-board DataFlash chip.
727 The +1g and -1g calibration points are included in each telemetry
728 frame and are part of the header extracted by ao-dumplog after flight.
729 Note that we always store and return raw ADC samples for each
730 sensor... nothing is permanently "lost" or "damaged" if the
737 <title>Using Altus Metrum Products</title>
739 <title>Being Legal</title>
741 First off, in the US, you need an [amateur radio license](../Radio) or
742 other authorization to legally operate the radio transmitters that are part
746 <title>In the Rocket</title>
748 In the rocket itself, you just need a [TeleMetrum](../TeleMetrum) board and
749 a LiPo rechargeable battery. An 860mAh battery weighs less than a 9V
750 alkaline battery, and will run a [TeleMetrum](../TeleMetrum) for hours.
753 By default, we ship TeleMetrum with a simple wire antenna. If your
754 electronics bay or the airframe it resides within is made of carbon fiber,
755 which is opaque to RF signals, you may choose to have an SMA connector
756 installed so that you can run a coaxial cable to an antenna mounted
757 elsewhere in the rocket.
761 <title>On the Ground</title>
763 To receive the data stream from the rocket, you need an antenna and short
764 feedline connected to one of our [TeleDongle](../TeleDongle) units. The
765 TeleDongle in turn plugs directly into the USB port on a notebook
766 computer. Because TeleDongle looks like a simple serial port, your computer
767 does not require special device drivers... just plug it in.
770 Right now, all of our application software is written for Linux. However,
771 because we understand that many people run Windows or MacOS, we are working
772 on a new ground station program written in Java that should work on all
776 After the flight, you can use the RF link to extract the more detailed data
777 logged in the rocket, or you can use a mini USB cable to plug into the
778 TeleMetrum board directly. Pulling out the data without having to open up
779 the rocket is pretty cool! A USB cable is also how you charge the LiPo
780 battery, so you'll want one of those anyway... the same cable used by lots
781 of digital cameras and other modern electronic stuff will work fine.
784 If your rocket lands out of sight, you may enjoy having a hand-held GPS
785 receiver, so that you can put in a waypoint for the last reported rocket
786 position before touch-down. This makes looking for your rocket a lot like
787 Geo-Cacheing... just go to the waypoint and look around starting from there.
790 You may also enjoy having a ham radio "HT" that covers the 70cm band... you
791 can use that with your antenna to direction-find the rocket on the ground
792 the same way you can use a Walston or Beeline tracker. This can be handy
793 if the rocket is hiding in sage brush or a tree, or if the last GPS position
794 doesn't get you close enough because the rocket dropped into a canyon, or
795 the wind is blowing it across a dry lake bed, or something like that... Keith
796 and Bdale both currently own and use the Yaesu VX-7R at launches.
799 So, to recap, on the ground the hardware you'll need includes:
800 <orderedlist inheritnum='inherit' numeration='arabic'>
802 an antenna and feedline
811 optionally, a handheld GPS receiver
814 optionally, an HT or receiver covering 435 Mhz
819 The best hand-held commercial directional antennas we've found for radio
820 direction finding rockets are from
821 <ulink url="http://www.arrowantennas.com/" >
824 The 440-3 and 440-5 are both good choices for finding a
825 TeleMetrum-equipped rocket when used with a suitable 70cm HT.
829 <title>Data Analysis</title>
831 Our software makes it easy to log the data from each flight, both the
832 telemetry received over the RF link during the flight itself, and the more
833 complete data log recorded in the DataFlash memory on the TeleMetrum
834 board. Once this data is on your computer, our postflight tools make it
835 easy to quickly get to the numbers everyone wants, like apogee altitude,
836 max acceleration, and max velocity. You can also generate and view a
837 standard set of plots showing the altitude, acceleration, and
838 velocity of the rocket during flight. And you can even export a data file
839 useable with Google Maps and Google Earth for visualizing the flight path
840 in two or three dimensions!
843 Our ultimate goal is to emit a set of files for each flight that can be
844 published as a web page per flight, or just viewed on your local disk with
849 <title>Future Plans</title>
851 In the future, we intend to offer "companion boards" for the rocket that will
852 plug in to TeleMetrum to collect additional data, provide more pyro channels,
853 and so forth. A reference design for a companion board will be documented
854 soon, and will be compatible with open source Arduino programming tools.
857 We are also working on the design of a hand-held ground terminal that will
858 allow monitoring the rocket's status, collecting data during flight, and
859 logging data after flight without the need for a notebook computer on the
860 flight line. Particularly since it is so difficult to read most notebook
861 screens in direct sunlight, we think this will be a great thing to have.
864 Because all of our work is open, both the hardware designs and the software,
865 if you have some great idea for an addition to the current Altus Metrum family,
866 feel free to dive in and help! Or let us know what you'd like to see that
867 we aren't already working on, and maybe we'll get excited about it too...