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