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 time. For
9 TeleMetrum, TeleMega and EasyMega, which have accelerometers, the mode is
10 controlled by the orientation of the
11 rocket (well, actually the board, of course...) at the time
12 power is switched on. If the rocket is “nose up”, then
13 the flight computer assumes it's on a rail or rod being prepared for
14 launch, so the firmware chooses flight mode. However, if the
15 rocket is more or less horizontal, the firmware instead enters
16 idle mode. Since TeleMini v2.0 and EasyMini don't have an
17 accelerometer we can use to determine orientation, “idle” mode
18 is selected if the board is connected via USB to a computer,
19 otherwise the board enters “flight” mode. TeleMini v1.0
20 selects “idle” mode if it receives a command packet within the
21 first five seconds of operation.
23 At power on, the altimeter will beep out the battery voltage
24 to the nearest tenth of a volt. Each digit is represented by
25 a sequence of short “dit” beeps, with a pause between
26 digits. A zero digit is represented with one long “dah”
27 beep. Then there will be a short pause while the altimeter
28 completes initialization and self test, and decides which mode
31 In flight or “pad” mode, the altimeter engages the flight
32 state machine, goes into transmit-only mode to send telemetry,
33 and waits for launch to be detected. Flight mode is indicated
34 by an “di-dah-dah-dit” (“P” for pad) on the beeper or lights,
35 followed by beeps or flashes indicating the state of the
36 pyrotechnic igniter continuity. One beep/flash indicates
37 apogee continuity, two beeps/flashes indicate main continuity,
38 three beeps/flashes indicate both apogee and main continuity,
39 and one longer “brap” sound which is made by rapidly
40 alternating between two tones indicates no continuity. For a
41 dual deploy flight, make sure you're getting three beeps or
42 flashes before launching! For apogee-only or motor eject
43 flights, do what makes sense.
45 If idle mode is entered, you will hear an audible “di-dit” or
46 see two short flashes (“I” for idle), and the flight state
47 machine is disengaged, thus no ejection charges will fire.
48 The altimeters also listen for the radio link when in idle
49 mode for requests sent via TeleDongle. Commands can be issued
50 in idle mode over either USB or the radio link
51 equivalently. TeleMini v1.0 only has the radio link. Idle
52 mode is useful for configuring the altimeter, for extracting
53 data from the on-board storage chip after flight, and for
54 ground testing pyro charges.
56 In “Idle” and “Pad” modes, once the mode indication
57 beeps/flashes and continuity indication has been sent, if
58 there is no space available to log the flight in on-board
59 memory, the flight computer will emit a warbling tone (much
60 slower than the “no continuity tone”)
62 Here's a summary of all of the “pad” and “idle” mode indications.
65 [options="header",cols="1,1,3"]
67 |Name |Beeps |Description
71 |No continuity detected on either apogee or main igniters.
75 |Continuity detected only on apogee igniter.
79 |Continuity detected only on main igniter.
84 |Continuity detected on both igniters.
89 |On-board data logging storage is full. This will
90 not prevent the flight computer from safely
91 controlling the flight or transmitting telemetry
92 signals, but no record of the flight will be
93 stored in on-board flash.
96 Once landed, the flight computer will signal that by emitting
97 the “Landed” sound described above, after which it will beep
98 out the apogee height (in meters). Each digit is represented
99 by a sequence of short “dit” beeps, with a pause between
100 digits. A zero digit is represented with one long “dah”
101 beep. The flight computer will continue to report landed mode
102 and beep out the maximum height until turned off.
104 One “neat trick” of particular value when TeleMetrum, TeleMega
105 or EasyMega are used with
106 very large air-frames, is that you can power the board up while the
107 rocket is horizontal, such that it comes up in idle mode. Then you can
108 raise the air-frame to launch position, and issue a 'reset' command
109 via TeleDongle over the radio link to cause the altimeter to reboot and
110 come up in flight mode. This is much safer than standing on the top
111 step of a rickety step-ladder or hanging off the side of a launch
112 tower with a screw-driver trying to turn on your avionics before
115 TeleMini v1.0 is configured solely via the radio link. Of course, that
116 means you need to know the TeleMini radio configuration values
117 or you won't be able to communicate with it. For situations
118 when you don't have the radio configuration values, TeleMini v1.0
119 offers an 'emergency recovery' mode. In this mode, TeleMini is
120 configured as follows:
123 * Sets the radio frequency to 434.550MHz
124 * Sets the radio calibration back to the factory value.
125 * Sets the callsign to N0CALL
126 * Does not go to 'pad' mode after five seconds.
128 To get into 'emergency recovery' mode, first find the row of
129 four small holes opposite the switch wiring. Using a short
130 piece of small gauge wire, connect the outer two holes
131 together, then power TeleMini up. Once the red LED is lit,
132 disconnect the wire and the board should signal that it's in
133 'idle' mode after the initial five second startup period.
137 TeleMetrum and TeleMega include a complete GPS receiver. A
138 complete explanation of how GPS works is beyond the scope of
139 this manual, but the bottom line is that the GPS receiver
140 needs to lock onto at least four satellites to obtain a solid
141 3 dimensional position fix and know what time it is.
143 The flight computers provide backup power to the GPS chip any time a
144 battery is connected. This allows the receiver to “warm start” on
145 the launch rail much faster than if every power-on were a GPS
146 “cold start”. In typical operations, powering up
147 on the flight line in idle mode while performing final air-frame
148 preparation will be sufficient to allow the GPS receiver to cold
149 start and acquire lock. Then the board can be powered down during
150 RSO review and installation on a launch rod or rail. When the board
151 is turned back on, the GPS system should lock very quickly, typically
152 long before igniter installation and return to the flight line are
155 === Controlling An Altimeter Over The Radio Link
157 One of the unique features of the Altus Metrum system is the
158 ability to create a two way command link between TeleDongle
159 and an altimeter using the digital radio transceivers
160 built into each device. This allows you to interact with the
161 altimeter from afar, as if it were directly connected to the
164 Any operation which can be performed with a flight computer can
165 either be done with the device directly connected to the
166 computer via the USB cable, or through the radio
167 link. TeleMini v1.0 doesn't provide a USB connector and so it is
168 always communicated with over radio. Select the appropriate
169 TeleDongle device when the list of devices is presented and
170 AltosUI will interact with an altimeter over the radio link.
172 One oddity in the current interface is how AltosUI selects the
173 frequency for radio communications. Instead of providing
174 an interface to specifically configure the frequency, it uses
175 whatever frequency was most recently selected for the target
176 TeleDongle device in Monitor Flight mode. If you haven't ever
177 used that mode with the TeleDongle in question, select the
178 Monitor Flight button from the top level UI, and pick the
179 appropriate TeleDongle device. Once the flight monitoring
180 window is open, select the desired frequency and then close it
181 down again. All radio communications will now use that frequency.
183 * Save Flight Data—Recover flight data from the
184 rocket without opening it up.
186 * Configure altimeter apogee delays, main deploy
187 heights and additional pyro event conditions to
188 respond to changing launch conditions. You can also
189 'reboot' the altimeter. Use this to remotely enable
190 the flight computer by turning TeleMetrum or
191 TeleMega on in “idle” mode, then once the air-frame
192 is oriented for launch, you can reboot the
193 altimeter and have it restart in pad mode without
194 having to climb the scary ladder.
196 * Fire Igniters—Test your deployment charges without snaking
197 wires out through holes in the air-frame. Simply assemble the
198 rocket as if for flight with the apogee and main charges
199 loaded, then remotely command the altimeter to fire the
202 Operation over the radio link for configuring an
203 altimeter, ground testing igniters, and so forth uses
204 the same RF frequencies as flight telemetry. To
205 configure the desired TeleDongle frequency, select the
206 monitor flight tab, then use the frequency selector
207 and close the window before performing other desired
210 The flight computers only enable radio commanding in
211 'idle' mode. TeleMetrum and TeleMega use the
212 accelerometer to detect which orientation they start
213 up in, so make sure you have the flight computer lying
214 horizontally when you turn it on. Otherwise, it will
215 start in 'pad' mode ready for flight, and will not be
216 listening for command packets from TeleDongle.
218 TeleMini listens for a command packet for five seconds
219 after first being turned on, if it doesn't hear
220 anything, it enters 'pad' mode, ready for flight and
221 will no longer listen for command packets. The easiest
222 way to connect to TeleMini is to initiate the command
223 and select the TeleDongle device. At this point, the
224 TeleDongle will be attempting to communicate with the
225 TeleMini. Now turn TeleMini on, and it should
226 immediately start communicating with the TeleDongle
227 and the desired operation can be performed.
229 You can monitor the operation of the radio link by watching the
230 lights on the devices. The red LED will flash each time a packet
231 is transmitted, while the green LED will light up on TeleDongle when
232 it is waiting to receive a packet from the altimeter.
236 An important aspect of preparing a rocket using electronic deployment
237 for flight is ground testing the recovery system. Thanks
238 to the bi-directional radio link central to the Altus Metrum system,
239 this can be accomplished in a TeleMega, TeleMetrum or TeleMini equipped rocket
240 with less work than you may be accustomed to with other systems. It
243 Just prep the rocket for flight, then power up the altimeter
244 in “idle” mode (placing air-frame horizontal for TeleMetrum or TeleMega, or
245 selecting the Configure Altimeter tab for TeleMini). This will cause
246 the firmware to go into “idle” mode, in which the normal flight
247 state machine is disabled and charges will not fire without
248 manual command. You can now command the altimeter to fire the apogee
249 or main charges from a safe distance using your computer and
250 TeleDongle and the Fire Igniter tab to complete ejection testing.
254 TeleMetrum, TeleMini and TeleMega all incorporate an
255 RF transceiver, but it's not a full duplex system;
256 each end can only be transmitting or receiving at any
257 given moment. So we had to decide how to manage the
260 By design, the altimeter firmware listens for the
261 radio link when it's in “idle mode”, which allows us
262 to use the radio link to configure the rocket, do
263 things like ejection tests, and extract data after a
264 flight without having to crack open the air-frame.
265 However, when the board is in “flight mode”, the
266 altimeter only transmits and doesn't listen at all.
267 That's because we want to put ultimate priority on
268 event detection and getting telemetry out of the
269 rocket through the radio in case the rocket crashes
270 and we aren't able to extract data later.
272 We don't generally use a 'normal packet radio' mode
273 like APRS because they're just too inefficient. The
274 GFSK modulation we use is FSK with the base-band
275 pulses passed through a Gaussian filter before they go
276 into the modulator to limit the transmitted bandwidth.
277 When combined with forward error correction and
278 interleaving, this allows us to have a very robust
279 19.2 kilobit data link with only 10-40 milliwatts of
280 transmit power, a whip antenna in the rocket, and a
281 hand-held Yagi on the ground. We've had flights to
282 above 21k feet AGL with great reception, and
283 calculations suggest we should be good to well over
284 40k feet AGL with a 5-element yagi on the ground with
285 our 10mW units and over 100k feet AGL with the 40mW
286 devices. We hope to fly boards to higher altitudes
287 over time, and would of course appreciate customer
288 feedback on performance in higher altitude flights!
290 :aprsdevices: TeleMetrum v2.0 and TeleMega
291 :configure_section: _configure_altimeter
292 include::aprs-operation.raw[]
294 === Configurable Parameters
296 Configuring an Altus Metrum altimeter for flight is
297 very simple. Even on our baro-only TeleMini and
298 EasyMini boards, the use of a Kalman filter means
299 there is no need to set a “mach delay”. All of the
300 configurable parameters can be set using AltosUI
301 over USB or or radio link via TeleDongle. Read
302 <<_configure_altimeter>> for more information.
projects / fw / altos / blob