1 = MicroPeak Owner's Manual
8 Thanks to John Lyngdal for suggesting that we build something
11 Have fun using these products, and we hope to meet all of you
12 out on the rocket flight line somewhere.
16 NAR #87103, TRA #12201
20 NAR #88757, TRA #12200
24 MicroPeak is designed to be easy to use. Requiring no external
25 components, flying takes just a few steps
29 Fit a CR1025 battery into the plastic carrier. The positive
30 (\+) terminal should be towards the more open side of the
31 carrier. Slip the carrier into the battery holder with the
32 positive (+) terminal facing away from the circuit board.
34 .MicroPeak and Battery
35 image::micropeak-back.jpg[width="4.5in"]
37 Install MicroPeak in your rocket::
39 This can be as simple as preparing a soft cushion of wadding
40 inside a vented model payload bay. Wherever you mount it,
41 make sure you protect the barometric sensor from corrosive
42 ejection gasses as those will damage the sensor, and shield
43 it from light as that can cause incorrect sensor readings.
47 Slide the switch so that the actuator covers the '1' printed
48 on the board. MicroPeak will report the maximum height of
49 the last flight in decimeters using a sequence of flashes on
50 the LED. A sequence of short flashes indicates one digit. A
51 single long flash indicates zero. The height is reported in
52 decimeters, so the last digit will be tenths of a meter. For
53 example, if MicroPeak reports 5 4 4 3, then the maximum
54 height of the last flight was 544.3m, or 1786 feet.
56 Finish preparing the rocket for flight::
58 After the previous flight data have been reported, MicroPeak
59 waits for one minute before starting to check for
60 launch. This gives you time to finish assembling the
61 rocket. As those activities might cause pressure changes
62 inside the airframe, MicroPeak might accidentally detect
63 boost. If you need to do anything to the airframe after the
64 one minute window passes, make sure to be careful not to
65 disturb the altimeter. The LED will remain dark during the
66 one minute delay, but after that, it will start blinking
71 Once the rocket passes about 30m in height (100 feet), the
72 micro-controller will record the ground pressure and track
73 the pressure seen during the flight. In this mode, the LED
74 flickers rapidly. When the rocket lands, and the pressure
75 stabilizes, the micro-controller will record the minimum
76 pressure pressure experienced during the flight, compute the
77 height represented by the difference in air pressure and
78 blink that value out on the LED. After that, MicroPeak
79 powers down to conserve battery power.
83 Turn MicroPeak off and then back on. MicroPeak will blink
84 out the maximum height for the last flight. Turn MicroPeak
85 back off to conserve battery power.
87 == The MicroPeak USB adapter
89 .MicroPeak USB Adapter
90 image::MicroPeakUSB-2.0.jpg[width="4.5in",align="center"]
92 MicroPeak stores barometric pressure information for the first
93 48 seconds of the flight in on-board non-volatile memory. The
94 contents of this memory can be downloaded to a computer using
95 the MicroPeak USB adapter.
97 === Installing the MicroPeak software
99 The MicroPeak application runs on Linux, Mac OS X and
100 Windows. You can download the latest version from
101 http://altusmetrum.org/MicroPeak
103 On Mac OS X and Windows, the FTDI USB device driver
104 needs to be installed. A compatible version of this
105 driver is included with the MicroPeak application, but
106 you may want to download a newer version from
107 http://www.ftdichip.com/FTDrivers.htm
109 === Downloading Micro Peak data
111 * Plug the MicroPeak USB adapter in to your computer.
113 * Start the MicroPeak application.
115 image::micropeak-nofont.svg[width="0.5in",align="center"]
117 * Click on the Download button at the top of the
120 .MicroPeak Application
121 image::micropeak-app.png[width="4.5in",align="center"]
123 * Select from the listed devices. There will probably
126 .MicroPeak Device Dialog
127 image::micropeak-device-dialog.png[width="2.3in",align="center"]
129 * The application will now wait until it receives
130 valid data from the MicroPeak USB adapter.
132 .MicroPeak Download Dialog
133 image::micropeak-download.png[width="2in",align="center"]
135 * The MicroPeak USB adapter has a small
136 phototransistor under the hole in the center of the
137 box. Locate this, turn on the MicroPeak and place
138 the orange LED on the MicroPeak directly inside the
139 hole, resting the MicroPeak itself on the box. You
140 should see the blue LED on the MicroPeak USB adapter
141 blinking in time with the orange LED on the
142 MicroPeak board itself.
144 .MicroPeak Downloading
145 image::MicroPeakUSB-2.0-inuse.jpg[width="4.5in",align="center"]
147 * After the maximum flight height is reported,
148 MicroPeak will pause for a few seconds, blink the
149 LED four times rapidly and then send the data in one
150 long blur on the LED. The MicroPeak application
151 should receive the data. When it does, it will
152 present the data in a graph and offer to save the
153 data to a file. If not, you can power cycle the
154 MicroPeak board and try again.
156 .MicroPeak Save Dialog
157 image::micropeak-save-dialog.png[width="2.3in",align="center"]
159 * Once the data are saved, a graph will be displayed
160 with height, speed and acceleration values computed
161 from the recorded barometric pressure data. See
162 <<_analyzing_micropeak_data> for more details on that.
164 === Analyzing MicroPeak Data
166 The MicroPeak application can present flight data in
167 the form of a graph, a collection of computed
168 statistics or in tabular form.
170 MicroPeak collects raw barometric pressure data which
171 is then used to compute the remaining data. Altitude
172 is computed through a standard atmospheric
173 model. Absolute error in this data will be affected by
174 local atmospheric conditions. Fortunately, these
175 errors tend to mostly cancel out, so the error in the
176 height computation is much smaller than the error in
179 Speed and acceleration are computed by first smoothing
180 the height data with a Gaussian window averaging
181 filter. For speed data, this average uses seven
182 samples. For acceleration data, eleven samples are
183 used. These were chosen to provide reasonably smooth
184 speed and acceleration data, which would otherwise be
187 The File menu has operations to open existing flight
188 logs, Download new data from MicroPeak, Save a copy of
189 the flight log to a new file, Export the tabular data
190 (as seen in the Raw Data tab) to a file, change the
191 application Preferences, Close the current window or
192 close all windows and Exit the application.
194 ==== MicroPeak Graphs
197 image::micropeak-graph.png[width="4.5in",align="center"]
199 Under the Graph tab, the height, speed and acceleration values
200 are displayed together. You can zoom in on the graph by
201 clicking and dragging to sweep out an area of
202 interest. Right-click on the plot to bring up a menu that will
203 let you save, copy or print the graph.
205 ==== MicroPeak Flight Statistics
207 .MicroPeak Flight Statistics
208 image::micropeak-statistics.png[width="4.5in",align="center"]
210 The Statistics tab presents overall data from
211 the flight. Note that the Maximum height value
212 is taken from the minumum pressure captured in
213 flight, and may be different from the apparant
214 apogee value as the on-board data are sampled
215 twice as fast as the recorded values, or
216 because the true apogee occurred after the
217 on-board memory was full. Each value is
218 presented in several units as appropriate.
222 .MicroPeak Raw Flight Data
223 image::micropeak-raw-data.png[width="4.5in",align="center"]
225 A table consisting of the both the raw barometric pressure
226 data and values computed from that for each recorded time.
228 ==== Configuring the Graph
230 .MicroPeak Graph Configuration
231 image::micropeak-graph-configure.png[width="4.5in",align="center"]
233 This selects which graph elements to show, and lets you
234 switch between metric and imperial units
236 === Setting MicroPeak Preferences
238 .MicroPeak Preferences
239 image::micropeak-preferences.png[width="1.8in",align="center"]
241 The MicroPeak application has a few user settings which are
242 configured through the Preferences dialog, which can be
243 accessed from the File menu.
247 The Log Directory is where flight data will be
248 saved to and loaded from by default. Of
249 course, you can always navigate to other
250 directories in the file chooser windows, this
251 setting is just the starting point.
255 If you prefer to see your graph data in feet
256 and miles per hour instead of meters and
257 meters per second, you can select Imperial
262 To see what data is actually arriving over the
263 serial port, start the MicroPeak application
264 from a command prompt and select the Serial
265 Debug option. This can be useful in debugging
266 serial communication problems, but most people
267 need never choose this.
271 You can adjust the size of the text in the
272 Statistics tab by changing the Font size
273 preference. There are three settings, with
274 luck one will both fit on your screen and
275 provide readable values.
279 The Look & feel menu shows a list of available
280 application appearance choices. By default,
281 the MicroPeak application tries to blend in
282 with other applications, but you may choose
283 some other appearance if you like.
285 Note that MicroPeak shares a subset of the
286 AltosUI preferences, so if you use both of
287 these applications, change in one application
288 will affect the other.
291 == Handling Precautions
293 All Altus Metrum products are sophisticated electronic
294 devices. When handled gently and properly installed in an
295 air-frame, they will deliver impressive results. However, as
296 with all electronic devices, there are some precautions you
301 The CR1025 Lithium batteries have an extraordinary power
302 density. This is great because we can fly with much less
303 battery mass... but if they are punctured or their contacts
304 are allowed to short, they can and will release their energy
305 very rapidly! Thus we recommend that you take some care when
306 handling MicroPeak to keep conductive material from coming in
307 contact with the exposed metal elements.
309 The barometric sensor used in MicroPeak is sensitive to
310 sunlight. Please consider this when designing an
311 installation. Many model rockets with payload bays use clear
312 plastic for the payload bay. Replacing these with an opaque
313 cardboard tube, painting them, or wrapping them with a layer
314 of masking tape are all reasonable approaches to keep the
315 sensor out of direct sunlight.
317 The barometric sensor sampling ports must be able to
318 "breathe", both by not being covered by foam or tape or other
319 materials that might directly block the hole on the top of the
320 sensor, and also by having a suitable static vent to outside
323 As with all other rocketry electronics, Altus Metrum
324 altimeters must be protected from exposure to corrosive motor
325 exhaust and ejection charge gasses.
328 == Technical Information
330 === Barometric Sensor
332 MicroPeak uses the Measurement Specialties MS5607
333 sensor. This has a range of 120kPa to 1kPa with an
334 absolute accuracy of 150Pa and a resolution of 2.4Pa.
336 The pressure range corresponds roughly to an altitude
337 range of -1500m (-4900 feet) to 31000m (102000 feet),
338 while the resolution is approximately 20cm (8 inches)
339 near sea level and 60cm (24in) at 10000m (33000 feet).
341 Ground pressure is computed from an average of 16
342 samples, taken while the altimeter is at rest. The
343 flight pressure used to report maximum height is
344 computed from a Kalman filter designed to smooth out
345 any minor noise in the sensor values. The flight
346 pressure recorded to non-volatile storage is
347 unfiltered, coming directly from the pressure sensor.
351 MicroPeak uses an Atmel ATtiny85
352 micro-controller. This tiny CPU contains 8kB of flash
353 for the application, 512B of RAM for temporary data
354 storage and 512B of EEPROM for non-volatile storage of
355 previous flight data.
357 The ATtiny85 has a low-power mode which turns off all
358 of the clocks and powers down most of the internal
359 components. In this mode, the chip consumes only .1μA
360 of power. MicroPeak uses this mode once the flight has
361 ended to preserve battery power.
365 The CR1025 battery used by MicroPeak holds 30mAh of
366 power, which is sufficient to run for over 40
367 hours. Because MicroPeak powers down on landing, run
368 time includes only time sitting on the launch pad or
371 The large positive terminal (+) is usually marked,
372 while the smaller negative terminal is not. Make sure
373 you install the battery with the positive terminal
374 facing away from the circuit board where it will be in
375 contact with the metal battery holder. A small pad on
376 the circuit board makes contact with the negative
379 Shipping restrictions may prevent us from including a
380 CR1025 battery with MicroPeak. If so, many stores
381 carry CR1025 batteries as they are commonly used in
382 small electronic devices such as flash lights.
384 === Atmospheric Model
386 MicroPeak contains a fixed atmospheric model which is
387 used to convert barometric pressure into altitude. The
388 model was converted into a 469-element piece-wise
389 linear approximation which is then used to compute the
390 altitude of the ground and apogee. The difference
391 between these represents the maximum height of the
394 The model assumes a particular set of atmospheric
395 conditions, which, while a reasonable average, cannot
396 represent the changing nature of the real
397 atmosphere. Fortunately, for flights reasonably close
398 to the ground, the effect of this global inaccuracy
399 are largely canceled out when the computed ground
400 altitude is subtracted from the computed apogee
401 altitude, so the resulting height is more accurate
402 than either the ground or apogee altitudes.
404 Because the raw pressure data is recorded to
405 non-volatile storage, you can use that, along with a
406 more sophisticated atmospheric model, to compute your
409 === Mechanical Considerations
411 MicroPeak is designed to be rugged enough for typical
412 rocketry applications. It contains two moving parts,
413 the battery holder and the power switch, which were
414 selected for their ruggedness.
416 The MicroPeak battery holder is designed to withstand
417 impact up to 150g without breaking contact (or, worse
418 yet, causing the battery to fall out). That means it
419 should stand up to almost any launch you care to try,
420 and should withstand fairly rough landings.
422 The power switch is designed to withstand up to 50g
423 forces in any direction. Because it is a sliding
424 switch, orienting the switch perpendicular to the
425 direction of rocket travel will serve to further
426 protect the switch from launch forces.
428 === MicroPeak Programming Interface
430 MicroPeak exposes a standard 6-pin AVR programming
431 interface, but not using the usual 2x3 array of pins
432 on 0.1" centers. Instead, there is a single row of
433 tiny 0.60mm × 0.85mm pads on 1.20mm centers exposed
434 near the edge of the circuit board. We couldn't find
435 any connector that was small enough to include on the
438 In lieu of an actual connector, the easiest way to
439 connect to the bare pads is through a set of Pogo
440 pins. These spring-loaded contacts are designed to
441 connect in precisely this way. We've designed a
442 programming jig, the MicroPeak Pogo Pin board which
443 provides a standard AVR interface on one end and a
444 recessed slot for MicroPeak to align the board with
447 The MicroPeak Pogo Pin board is not a complete AVR
448 programmer, it is an interface board that provides a
449 3.3V regulated power supply to run the MicroPeak via
450 USB and a standard 6-pin AVR programming interface
451 with the usual 2x3 grid of pins on 0.1" centers. This
452 can be connected to any AVR programming dongle.
454 The AVR programming interface cannot run faster than ¼
455 of the AVR CPU clock frequency. Because MicroPeak runs
456 at 250kHz to save power, you must configure your AVR
457 programming system to clock the AVR programming
458 interface at no faster than 62.5kHz, or a clock period
462 == On-board data storage
464 The ATtiny85 has 512 bytes of non-volatile storage, separate
465 from the code storage memory. The MicroPeak firmware uses this
466 to store information about the last completed
467 flight. Barometric measurements from the ground before launch
468 and at apogee are stored, and used at power-on to compute the
469 height of the last flight.
471 In addition to the data used to present the height of the last
472 flight, MicroPeak also stores barometric information sampled
473 at regular intervals during the flight. This is the
474 information captured with the MicroPeak USB adapter. It can
475 also be read from MicroPeak through any AVR programming tool.
478 .MicroPeak EEPROM Data Storage
479 [options="border",cols="2,1,7"]
481 |Address |Size (bytes) |Description
482 |0x000 |4 |Average ground pressure (Pa)
483 |0x004 |4 |Minimum flight pressure (Pa)
484 |0x008 |2 |Number of in-flight samples
485 |0x00a … 0x1fe |2 |Instantaneous flight pressure (Pa) low 16 bits
488 All EEPROM data are stored least-significant byte first. The
489 instantaneous flight pressure data are stored without the
490 upper 16 bits of data. The upper bits can be reconstructed
491 from the previous sample, assuming that pressure doesn't
492 change by more more than 32kPa in a single sample
493 interval. Note that this pressure data is *not* filtered in
494 any way, while both the recorded ground and apogee pressure
495 values are, so you shouldn't expect the minimum instantaneous
496 pressure value to match the recorded minimum pressure value
499 MicroPeak samples pressure every 96ms, but stores only every
500 other sample in the EEPROM. This provides for 251 pressure
501 samples at 192ms intervals, or 48.192s of storage. The clock
502 used for these samples is a factory calibrated RC circuit
503 built into the ATtiny85 and is accurate only to within ±10% at
504 25°C. So, you can count on the pressure data being accurate,
505 but speed or acceleration data computed from this will be
506 limited by the accuracy of this clock.