6 The AltOS firmware build for the altimeters has two
7 fundamental modes, “idle” and “flight”. Which of these modes
8 the firmware operates in is determined at start up
10 ifdef::telemetrum,telemega,easymega[]
12 TeleMetrum, TeleMega and EasyMega, which have accelerometers, the mode is
13 controlled by the orientation of the
14 rocket (well, actually the board, of course...) at the time
15 power is switched on. If the rocket is “nose up”, then
16 the flight computer assumes it's on a rail or rod being prepared for
17 launch, so the firmware chooses flight mode. However, if the
18 rocket is more or less horizontal, the firmware instead enters
20 endif::telemetrum,telemega,easymega[]
24 accelerometer we can use to determine orientation, “idle” mode
25 is selected if the board is connected via USB to a computer,
26 otherwise the board enters “flight” mode.
29 selects “idle” mode if it receives a command packet within the
30 first five seconds of operation.
33 At power on, the altimeter will beep out the battery voltage
34 to the nearest tenth of a volt. Each digit is represented by
35 a sequence of short “dit” beeps, with a pause between
36 digits. A zero digit is represented with one long “dah”
37 beep. Then there will be a short pause while the altimeter
38 completes initialization and self test, and decides which mode
41 In flight or “pad” mode, the altimeter engages the flight
42 state machine, goes into transmit-only mode to send telemetry,
43 and waits for launch to be detected. Flight mode is indicated
44 by an “di-dah-dah-dit” (“P” for pad) on the beeper or lights,
45 followed by beeps or flashes indicating the state of the
46 pyrotechnic igniter continuity. One beep/flash indicates
47 apogee continuity, two beeps/flashes indicate main continuity,
48 three beeps/flashes indicate both apogee and main continuity,
49 and one longer “brap” sound which is made by rapidly
50 alternating between two tones indicates no continuity. For a
51 dual deploy flight, make sure you're getting three beeps or
52 flashes before launching! For apogee-only or motor eject
53 flights, do what makes sense.
55 If idle mode is entered, you will hear an audible “di-dit” or
56 see two short flashes (“I” for idle), and the flight state
57 machine is disengaged, thus no ejection charges will fire.
59 The altimeters also listen for the radio link when in idle
60 mode for requests sent via TeleDongle. Commands can be issued
61 in idle mode over either USB or the radio link
63 ifdef::telemini[TeleMini v1.0 only has the radio link.]
65 Idle mode is useful for configuring the altimeter, for
66 extracting data from the on-board storage chip after
67 flight, and for ground testing pyro charges.
69 In “Idle” and “Pad” modes, once the mode indication
70 beeps/flashes and continuity indication has been sent, if
71 there is no space available to log the flight in on-board
72 memory, the flight computer will emit a warbling tone (much
73 slower than the “no continuity tone”)
75 See <<_understanding_beeps>> for a summary of all of
76 the audio signals used.
78 Once landed, the flight computer will signal that by emitting
79 the “Landed” sound described above, after which it will beep
80 out the apogee height (in meters). Each digit is represented
81 by a sequence of short “dit” beeps, with a pause between
82 digits. A zero digit is represented with one long “dah”
83 beep. The flight computer will continue to report landed mode
84 and beep out the maximum height until turned off.
86 ifdef::telemetrum,telemega,easymega[]
87 One “neat trick” of particular value when TeleMetrum, TeleMega
88 or EasyMega are used with
89 very large air-frames, is that you can power the board up while the
90 rocket is horizontal, such that it comes up in idle mode. Then you can
91 raise the air-frame to launch position, and issue a 'reset' command
92 via TeleDongle over the radio link to cause the altimeter to reboot and
93 come up in flight mode. This is much safer than standing on the top
94 step of a rickety step-ladder or hanging off the side of a launch
95 tower with a screw-driver trying to turn on your avionics before
97 endif::telemetrum,telemega,easymega[]
100 TeleMini v1.0 is configured solely via the radio link. Of course, that
101 means you need to know the TeleMini radio configuration values
102 or you won't be able to communicate with it. For situations
103 when you don't have the radio configuration values, TeleMini v1.0
104 offers an 'emergency recovery' mode. In this mode, TeleMini is
105 configured as follows:
108 * Sets the radio frequency to 434.550MHz
109 * Sets the radio calibration back to the factory value.
110 * Sets the callsign to N0CALL
111 * Does not go to 'pad' mode after five seconds.
113 To get into 'emergency recovery' mode, first find the row of
114 four small holes opposite the switch wiring. Using a short
115 piece of small gauge wire, connect the outer two holes
116 together, then power TeleMini up. Once the red LED is lit,
117 disconnect the wire and the board should signal that it's in
118 'idle' mode after the initial five second startup
125 TeleMetrum and TeleMega include a complete GPS receiver. A
126 complete explanation of how GPS works is beyond the scope of
127 this manual, but the bottom line is that the GPS receiver
128 needs to lock onto at least four satellites to obtain a solid
129 3 dimensional position fix and know what time it is.
131 The flight computers provide backup power to the GPS chip any time a
132 battery is connected. This allows the receiver to “warm start” on
133 the launch rail much faster than if every power-on were a GPS
134 “cold start”. In typical operations, powering up
135 on the flight line in idle mode while performing final air-frame
136 preparation will be sufficient to allow the GPS receiver to cold
137 start and acquire lock. Then the board can be powered down during
138 RSO review and installation on a launch rod or rail. When the board
139 is turned back on, the GPS system should lock very quickly, typically
140 long before igniter installation and return to the flight line are
145 === Controlling An Altimeter Over The Radio Link
147 One of the unique features of the Altus Metrum system is the
148 ability to create a two way command link between TeleDongle
149 and an altimeter using the digital radio transceivers
150 built into each device. This allows you to interact with the
151 altimeter from afar, as if it were directly connected to the
154 Any operation which can be performed with a flight computer can
155 either be done with the device directly connected to the
156 computer via the USB cable, or through the radio
157 link. TeleMini v1.0 doesn't provide a USB connector and so it is
158 always communicated with over radio. Select the appropriate
159 TeleDongle device when the list of devices is presented and
160 AltosUI will interact with an altimeter over the radio link.
162 One oddity in the current interface is how AltosUI selects the
163 frequency for radio communications. Instead of providing
164 an interface to specifically configure the frequency, it uses
165 whatever frequency was most recently selected for the target
166 TeleDongle device in Monitor Flight mode. If you haven't ever
167 used that mode with the TeleDongle in question, select the
168 Monitor Flight button from the top level UI, and pick the
169 appropriate TeleDongle device. Once the flight monitoring
170 window is open, select the desired frequency and then close it
171 down again. All radio communications will now use that frequency.
173 * Save Flight Data—Recover flight data from the
174 rocket without opening it up.
176 * Configure altimeter apogee delays, main deploy
177 heights and additional pyro event conditions to
178 respond to changing launch conditions. You can also
179 'reboot' the altimeter. Use this to remotely enable
180 the flight computer by turning TeleMetrum or
181 TeleMega on in “idle” mode, then once the air-frame
182 is oriented for launch, you can reboot the
183 altimeter and have it restart in pad mode without
184 having to climb the scary ladder.
186 * Fire Igniters—Test your deployment charges without snaking
187 wires out through holes in the air-frame. Simply assemble the
188 rocket as if for flight with the apogee and main charges
189 loaded, then remotely command the altimeter to fire the
192 Operation over the radio link for configuring an
193 altimeter, ground testing igniters, and so forth uses
194 the same RF frequencies as flight telemetry. To
195 configure the desired TeleDongle frequency, select the
196 monitor flight tab, then use the frequency selector
197 and close the window before performing other desired
200 The flight computers only enable radio commanding in
201 'idle' mode. TeleMetrum and TeleMega use the
202 accelerometer to detect which orientation they start
203 up in, so make sure you have the flight computer lying
204 horizontally when you turn it on. Otherwise, it will
205 start in 'pad' mode ready for flight, and will not be
206 listening for command packets from TeleDongle.
208 TeleMini listens for a command packet for five seconds
209 after first being turned on, if it doesn't hear
210 anything, it enters 'pad' mode, ready for flight and
211 will no longer listen for command packets. The easiest
212 way to connect to TeleMini is to initiate the command
213 and select the TeleDongle device. At this point, the
214 TeleDongle will be attempting to communicate with the
215 TeleMini. Now turn TeleMini on, and it should
216 immediately start communicating with the TeleDongle
217 and the desired operation can be performed.
219 You can monitor the operation of the radio link by watching the
220 lights on the devices. The red LED will flash each time a packet
221 is transmitted, while the green LED will light up on TeleDongle when
222 it is waiting to receive a packet from the altimeter.
227 An important aspect of preparing a rocket using electronic deployment
228 for flight is ground testing the recovery system.
231 to the bi-directional radio link central to the Altus Metrum system,
232 this can be accomplished in a TeleMega, TeleMetrum or TeleMini equipped rocket
233 with less work than you may be accustomed to with other systems. It
237 Just prep the rocket for flight, then power up the altimeter
239 ifdef::telemetrum,telemega,telemini[]
240 mode (placing air-frame horizontal for TeleMetrum or TeleMega, or
241 selecting the Configure Altimeter tab for TeleMini).
243 the firmware to go into “idle” mode, in which the normal flight
244 state machine is disabled and charges will not fire without
246 endif::telemetrum,telemega,telemini[]
247 ifndef::telemetrum,telemega,telemini[]
249 endif::telemetrum,telemega,telemini[]
250 You can now command the altimeter to fire the apogee
251 or main charges from a safe distance using your
252 computer and the Fire Igniter tab to complete ejection testing.
257 TeleMetrum, TeleMini and TeleMega all incorporate an
258 RF transceiver, but it's not a full duplex system;
259 each end can only be transmitting or receiving at any
260 given moment. So we had to decide how to manage the
263 By design, the altimeter firmware listens for the
264 radio link when it's in “idle mode”, which allows us
265 to use the radio link to configure the rocket, do
266 things like ejection tests, and extract data after a
267 flight without having to crack open the air-frame.
268 However, when the board is in “flight mode”, the
269 altimeter only transmits and doesn't listen at all.
270 That's because we want to put ultimate priority on
271 event detection and getting telemetry out of the
272 rocket through the radio in case the rocket crashes
273 and we aren't able to extract data later.
275 We don't generally use a 'normal packet radio' mode
276 like APRS because they're just too inefficient. The
277 GFSK modulation we use is FSK with the base-band
278 pulses passed through a Gaussian filter before they go
279 into the modulator to limit the transmitted bandwidth.
280 When combined with forward error correction and
281 interleaving, this allows us to have a very robust
282 19.2 kilobit data link with only 10-40 milliwatts of
283 transmit power, a whip antenna in the rocket, and a
284 hand-held Yagi on the ground. We've had flights to
285 above 21k feet AGL with great reception, and
286 calculations suggest we should be good to well over
287 40k feet AGL with a 5-element yagi on the ground with
288 our 10mW units and over 100k feet AGL with the 40mW
289 devices. We hope to fly boards to higher altitudes
290 over time, and would of course appreciate customer
291 feedback on performance in higher altitude flights!
295 :aprsdevices: TeleMetrum v2.0 and TeleMega
296 :configure_section: _configure_altimeter
297 include::aprs-operation.raw[]
300 === Configurable Parameters
302 Configuring an Altus Metrum altimeter for flight is
303 very simple. Even on our baro-only TeleMini and
304 EasyMini boards, the use of a Kalman filter means
305 there is no need to set a “mach delay”. All of the
306 configurable parameters can be set using AltosUI. Read
307 <<_configure_altimeter>> for more information.
projects / fw / altos / blob