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[]
22 ifdef::telemini[TeleMini v2.0 and EasyMini don't]
23 ifndef::telemini[EasyMini doesn't]
25 accelerometer we can use to determine orientation, “idle” mode
26 is selected if the board is connected via USB to a computer,
27 otherwise the board enters “flight” mode.
30 selects “idle” mode if it receives a command packet within the
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 v1.0 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 v1.0 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, TeleMini v1.0
105 offers an 'emergency recovery' mode. In this mode, TeleMini is
106 configured as follows:
109 * Sets the radio frequency to 434.550MHz
110 * Sets the radio calibration back to the factory value.
111 * Sets the callsign to N0CALL
112 * Does not go to 'pad' mode after five seconds.
114 To get into 'emergency recovery' mode, first find the row of
115 four small holes opposite the switch wiring. Using a short
116 piece of small gauge wire, connect the outer two holes
117 together, then power TeleMini up. Once the red LED is lit,
118 disconnect the wire and the board should signal that it's in
119 'idle' mode after the initial five second startup
126 TeleMetrum and TeleMega include a complete GPS receiver. A
127 complete explanation of how GPS works is beyond the scope of
128 this manual, but the bottom line is that the GPS receiver
129 needs to lock onto at least four satellites to obtain a solid
130 3 dimensional position fix and know what time it is.
132 The flight computers provide backup power to the GPS chip any time a
133 battery is connected. This allows the receiver to “warm start” on
134 the launch rail much faster than if every power-on were a GPS
135 “cold start”. In typical operations, powering up
136 on the flight line in idle mode while performing final air-frame
137 preparation will be sufficient to allow the GPS receiver to cold
138 start and acquire lock. Then the board can be powered down during
139 RSO review and installation on a launch rod or rail. When the board
140 is turned back on, the GPS system should lock very quickly, typically
141 long before igniter installation and return to the flight line are
146 === Controlling An Altimeter Over The Radio Link
148 One of the unique features of the Altus Metrum system is the
149 ability to create a two way command link between TeleDongle
150 and an altimeter using the digital radio transceivers
151 built into each device. This allows you to interact with the
152 altimeter from afar, as if it were directly connected to the
155 Any operation which can be performed with a flight computer can
156 either be done with the device directly connected to the
157 computer via the USB cable, or through the radio
158 link. TeleMini v1.0 doesn't provide a USB connector and so it is
159 always communicated with over radio. Select the appropriate
160 TeleDongle device when the list of devices is presented and
161 AltosUI will interact with an altimeter over the radio link.
163 One oddity in the current interface is how AltosUI selects the
164 frequency for radio communications. Instead of providing
165 an interface to specifically configure the frequency, it uses
166 whatever frequency was most recently selected for the target
167 TeleDongle device in Monitor Flight mode. If you haven't ever
168 used that mode with the TeleDongle in question, select the
169 Monitor Flight button from the top level UI, and pick the
170 appropriate TeleDongle device. Once the flight monitoring
171 window is open, select the desired frequency and then close it
172 down again. All radio communications will now use that frequency.
174 * Save Flight Data—Recover flight data from the
175 rocket without opening it up.
177 * Configure altimeter apogee delays, main deploy
178 heights and additional pyro event conditions to
179 respond to changing launch conditions. You can also
180 'reboot' the altimeter. Use this to remotely enable
181 the flight computer by turning TeleMetrum or
182 TeleMega on in “idle” mode, then once the air-frame
183 is oriented for launch, you can reboot the
184 altimeter and have it restart in pad mode without
185 having to climb the scary ladder.
187 * Fire Igniters—Test your deployment charges without snaking
188 wires out through holes in the air-frame. Simply assemble the
189 rocket as if for flight with the apogee and main charges
190 loaded, then remotely command the altimeter to fire the
193 Operation over the radio link for configuring an
194 altimeter, ground testing igniters, and so forth uses
195 the same RF frequencies as flight telemetry. To
196 configure the desired TeleDongle frequency, select the
197 monitor flight tab, then use the frequency selector
198 and close the window before performing other desired
201 The flight computers only enable radio commanding in
202 'idle' mode. TeleMetrum and TeleMega use the
203 accelerometer to detect which orientation they start
204 up in, so make sure you have the flight computer lying
205 horizontally when you turn it on. Otherwise, it will
206 start in 'pad' mode ready for flight, and will not be
207 listening for command packets from TeleDongle.
209 TeleMini listens for a command packet for five seconds
210 after first being turned on, if it doesn't hear
211 anything, it enters 'pad' mode, ready for flight and
212 will no longer listen for command packets. The easiest
213 way to connect to TeleMini is to initiate the command
214 and select the TeleDongle device. At this point, the
215 TeleDongle will be attempting to communicate with the
216 TeleMini. Now turn TeleMini on, and it should
217 immediately start communicating with the TeleDongle
218 and the desired operation can be performed.
220 You can monitor the operation of the radio link by watching the
221 lights on the devices. The red LED will flash each time a packet
222 is transmitted, while the green LED will light up on TeleDongle when
223 it is waiting to receive a packet from the altimeter.
228 An important aspect of preparing a rocket using electronic deployment
229 for flight is ground testing the recovery system.
232 to the bi-directional radio link central to the Altus Metrum system,
233 this can be accomplished in a TeleMega, TeleMetrum or TeleMini equipped rocket
234 with less work than you may be accustomed to with other systems. It
238 Just prep the rocket for flight, then power up the altimeter
240 ifdef::telemetrum,telemega,telemini[]
241 mode (placing air-frame horizontal for TeleMetrum or TeleMega, or
242 selecting the Configure Altimeter tab for TeleMini).
244 the firmware to go into “idle” mode, in which the normal flight
245 state machine is disabled and charges will not fire without
247 endif::telemetrum,telemega,telemini[]
248 ifndef::telemetrum,telemega,telemini[]
250 endif::telemetrum,telemega,telemini[]
251 You can now command the altimeter to fire the apogee
252 or main charges from a safe distance using your
253 computer and the Fire Igniter tab to complete ejection testing.
258 TeleMetrum, TeleMini and TeleMega all incorporate an
259 RF transceiver, but it's not a full duplex system;
260 each end can only be transmitting or receiving at any
261 given moment. So we had to decide how to manage the
264 By design, the altimeter firmware listens for the
265 radio link when it's in “idle mode”, which allows us
266 to use the radio link to configure the rocket, do
267 things like ejection tests, and extract data after a
268 flight without having to crack open the air-frame.
269 However, when the board is in “flight mode”, the
270 altimeter only transmits and doesn't listen at all.
271 That's because we want to put ultimate priority on
272 event detection and getting telemetry out of the
273 rocket through the radio in case the rocket crashes
274 and we aren't able to extract data later.
276 We don't generally use a 'normal packet radio' mode
277 like APRS because they're just too inefficient. The
278 GFSK modulation we use is FSK with the base-band
279 pulses passed through a Gaussian filter before they go
280 into the modulator to limit the transmitted bandwidth.
281 When combined with forward error correction and
282 interleaving, this allows us to have a very robust
283 19.2 kilobit data link with only 10-40 milliwatts of
284 transmit power, a whip antenna in the rocket, and a
285 hand-held Yagi on the ground. We've had flights to
286 above 21k feet AGL with great reception, and
287 calculations suggest we should be good to well over
288 40k feet AGL with a 5-element yagi on the ground with
289 our 10mW units and over 100k feet AGL with the 40mW
290 devices. We hope to fly boards to higher altitudes
291 over time, and would of course appreciate customer
292 feedback on performance in higher altitude flights!
296 :aprsdevices: TeleMetrum v2.0 and TeleMega
297 :configure_section: _configure_altimeter
298 include::aprs-operation.raw[]
301 === Configurable Parameters
303 Configuring an Altus Metrum altimeter for flight is
304 very simple. Even on our baro-only TeleMini and
305 EasyMini boards, the use of a Kalman filter means
306 there is no need to set a “mach delay”. All of the
307 configurable parameters can be set using AltosUI. Read
308 <<_configure_altimeter>> for more information.
projects / fw / altos / blob