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
27 * Install the battery. Fit a CR1025 battery into the plastic
28 carrier. The positive (\+) terminal should be towards the more
29 open side of the carrier. Slip the carrier into the battery
30 holder with the positive (+) terminal facing away from the
33 .MicroPeak and Battery
34 image::micropeak-back.jpg[width="4.5in"]
36 * Install MicroPeak in your rocket. This can be as simple as
37 preparing a soft cushion of wadding inside a vented model payload
38 bay. Wherever you mount it, make sure you protect the
39 barometric sensor from corrosive ejection gasses as those
40 will damage the sensor, and shield it from light as that can
41 cause incorrect sensor readings.
43 * Turn MicroPeak on. Slide the switch so that the actuator
44 covers the '1' printed on the board. MicroPeak will report
45 the maximum height of the last flight in decimeters using a
46 sequence of flashes on the LED. A sequence of short flashes
47 indicates one digit. A single long flash indicates zero. The
48 height is reported in decimeters, so the last digit will be
49 tenths of a meter. For example, if MicroPeak reports 5 4 4
50 3, then the maximum height of the last flight was 544.3m, or
53 * Finish preparing the rocket for flight. After the
54 previous flight data have been reported, MicroPeak waits for
55 one minute before starting to check for launch. This gives
56 you time to finish assembling the rocket. As those
57 activities might cause pressure changes inside the airframe,
58 MicroPeak might accidentally detect boost. If you need to do
59 anything to the airframe after the one minute window passes,
60 make sure to be careful not to disturb the altimeter. The
61 LED will remain dark during the one minute delay, but after
62 that, it will start blinking once every 3 seconds.
64 * Fly the rocket. Once the rocket passes about 30m in height
65 (100 feet), the micro-controller will record the ground
66 pressure and track the pressure seen during the flight. In
67 this mode, the LED flickers rapidly. When the rocket lands,
68 and the pressure stabilizes, the micro-controller will record
69 the minimum pressure pressure experienced during the flight,
70 compute the height represented by the difference in air
71 pressure and blink that value out on the LED. After that,
72 MicroPeak powers down to conserve battery power.
74 * Recover the data. Turn MicroPeak off and then back on. MicroPeak
75 will blink out the maximum height for the last flight. Turn
76 MicroPeak back off to conserve battery power.
78 == The MicroPeak USB adapter
80 .MicroPeak USB Adapter
81 image::MicroPeakUSB-2.0.jpg[width="4.5in"]
83 MicroPeak stores barometric pressure information for the first
84 48 seconds of the flight in on-board non-volatile memory. The
85 contents of this memory can be downloaded to a computer using
86 the MicroPeak USB adapter.
88 === Installing the MicroPeak software
90 The MicroPeak application runs on Linux, Mac OS X and
91 Windows. You can download the latest version from
92 http://altusmetrum.org/MicroPeak
94 On Mac OS X and Windows, the FTDI USB device driver
95 needs to be installed. A compatible version of this
96 driver is included with the MicroPeak application, but
97 you may want to download a newer version from
98 http://www.ftdichip.com/FTDrivers.htm
100 === Downloading Micro Peak data
102 * Plug the MicroPeak USB adapter in to your computer.
104 * Start the MicroPeak application.
106 image::micropeak-nofont.svg[width="0.5in"]
108 * Click on the Download button at the top of the
111 .MicroPeak Application
112 image::micropeak-app.png[width="4.5in"]
114 * Select from the listed devices. There will probably
117 .MicroPeak Device Dialog
118 image::micropeak-device-dialog.png[width="2.3in"]
120 * The application will now wait until it receives
121 valid data from the MicroPeak USB adapter.
123 .MicroPeak Download Dialog
124 image::micropeak-download.png[width="2in"]
126 * The MicroPeak USB adapter has a small
127 phototransistor under the hole in the center of the
128 box. Locate this, turn on the MicroPeak and place
129 the orange LED on the MicroPeak directly inside the
130 hole, resting the MicroPeak itself on the box. You
131 should see the blue LED on the MicroPeak USB adapter
132 blinking in time with the orange LED on the
133 MicroPeak board itself.
135 .MicroPeak Downloading
136 image::MicroPeakUSB-2.0-inuse.jpg[width="4.5in"]
138 * After the maximum flight height is reported,
139 MicroPeak will pause for a few seconds, blink the
140 LED four times rapidly and then send the data in one
141 long blur on the LED. The MicroPeak application
142 should receive the data. When it does, it will
143 present the data in a graph and offer to save the
144 data to a file. If not, you can power cycle the
145 MicroPeak board and try again.
147 .MicroPeak Save Dialog
148 image::micropeak-save-dialog.png[width="2.3in"]
150 * Once the data are saved, a graph will be displayed
151 with height, speed and acceleration values computed
152 from the recorded barometric pressure data. See the
153 next section for more details on that.
155 === Analyzing MicroPeak Data
157 The MicroPeak application can present flight data in
158 the form of a graph, a collection of computed
159 statistics or in tabular form.
161 MicroPeak collects raw barometric pressure data which
162 is then used to compute the remaining data. Altitude
163 is computed through a standard atmospheric
164 model. Absolute error in this data will be affected by
165 local atmospheric conditions. Fortunately, these
166 errors tend to mostly cancel out, so the error in the
167 height computation is much smaller than the error in
170 Speed and acceleration are computed by first smoothing
171 the height data with a Gaussian window averaging
172 filter. For speed data, this average uses seven
173 samples. For acceleration data, eleven samples are
174 used. These were chosen to provide reasonably smooth
175 speed and acceleration data, which would otherwise be
178 The File menu has operations to open existing flight
179 logs, Download new data from MicroPeak, Save a copy of
180 the flight log to a new file, Export the tabular data
181 (as seen in the Raw Data tab) to a file, change the
182 application Preferences, Close the current window or
183 close all windows and Exit the application.
185 ==== MicroPeak Graphs
188 image::micropeak-graph.png[width="4.5in"]
190 Under the Graph tab, the height, speed and acceleration values
191 are displayed together. You can zoom in on the graph by
192 clicking and dragging to sweep out an area of
193 interest. Right-click on the plot to bring up a menu that will
194 let you save, copy or print the graph.
196 ==== MicroPeak Flight Statistics
198 .MicroPeak Flight Statistics
199 image::micropeak-statistics.png[width="4.5in"]
201 The Statistics tab presents overall data from
202 the flight. Note that the Maximum height value
203 is taken from the minumum pressure captured in
204 flight, and may be different from the apparant
205 apogee value as the on-board data are sampled
206 twice as fast as the recorded values, or
207 because the true apogee occurred after the
208 on-board memory was full. Each value is
209 presented in several units as appropriate.
213 .MicroPeak Raw Flight Data
214 image::micropeak-raw-data.png[width="4.5in"]
216 A table consisting of the both the raw barometric pressure
217 data and values computed from that for each recorded time.
219 ==== Configuring the Graph
221 .MicroPeak Graph Configuration
222 image::micropeak-graph-configure.png[width="4.5in"]
224 This selects which graph elements to show, and lets you
225 switch between metric and imperial units
227 === Setting MicroPeak Preferences
229 .MicroPeak Preferences
230 image::micropeak-preferences.png[width="1.8in"]
232 The MicroPeak application has a few user settings which are
233 configured through the Preferences dialog, which can be
234 accessed from the File menu.
238 The Log Directory is where flight data will be
239 saved to and loaded from by default. Of
240 course, you can always navigate to other
241 directories in the file chooser windows, this
242 setting is just the starting point.
246 If you prefer to see your graph data in feet
247 and miles per hour instead of meters and
248 meters per second, you can select Imperial
253 To see what data is actually arriving over the
254 serial port, start the MicroPeak application
255 from a command prompt and select the Serial
256 Debug option. This can be useful in debugging
257 serial communication problems, but most people
258 need never choose this.
262 You can adjust the size of the text in the
263 Statistics tab by changing the Font size
264 preference. There are three settings, with
265 luck one will both fit on your screen and
266 provide readable values.
270 The Look & feel menu shows a list of available
271 application appearance choices. By default,
272 the MicroPeak application tries to blend in
273 with other applications, but you may choose
274 some other appearance if you like.
276 Note that MicroPeak shares a subset of the
277 AltosUI preferences, so if you use both of
278 these applications, change in one application
279 will affect the other.
282 == Handling Precautions
284 All Altus Metrum products are sophisticated electronic
285 devices. When handled gently and properly installed in an
286 air-frame, they will deliver impressive results. However, as
287 with all electronic devices, there are some precautions you
292 The CR1025 Lithium batteries have an extraordinary power
293 density. This is great because we can fly with much less
294 battery mass... but if they are punctured or their contacts
295 are allowed to short, they can and will release their energy
296 very rapidly! Thus we recommend that you take some care when
297 handling MicroPeak to keep conductive material from coming in
298 contact with the exposed metal elements.
300 The barometric sensor used in MicroPeak is sensitive to
301 sunlight. Please consider this when designing an
302 installation. Many model rockets with payload bays use clear
303 plastic for the payload bay. Replacing these with an opaque
304 cardboard tube, painting them, or wrapping them with a layer
305 of masking tape are all reasonable approaches to keep the
306 sensor out of direct sunlight.
308 The barometric sensor sampling ports must be able to
309 "breathe", both by not being covered by foam or tape or other
310 materials that might directly block the hole on the top of the
311 sensor, and also by having a suitable static vent to outside
314 As with all other rocketry electronics, Altus Metrum
315 altimeters must be protected from exposure to corrosive motor
316 exhaust and ejection charge gasses.
319 == Technical Information
321 === Barometric Sensor
323 MicroPeak uses the Measurement Specialties MS5607
324 sensor. This has a range of 120kPa to 1kPa with an
325 absolute accuracy of 150Pa and a resolution of 2.4Pa.
327 The pressure range corresponds roughly to an altitude
328 range of -1500m (-4900 feet) to 31000m (102000 feet),
329 while the resolution is approximately 20cm (8 inches)
330 near sea level and 60cm (24in) at 10000m (33000 feet).
332 Ground pressure is computed from an average of 16
333 samples, taken while the altimeter is at rest. The
334 flight pressure used to report maximum height is
335 computed from a Kalman filter designed to smooth out
336 any minor noise in the sensor values. The flight
337 pressure recorded to non-volatile storage is
338 unfiltered, coming directly from the pressure sensor.
342 MicroPeak uses an Atmel ATtiny85
343 micro-controller. This tiny CPU contains 8kB of flash
344 for the application, 512B of RAM for temporary data
345 storage and 512B of EEPROM for non-volatile storage of
346 previous flight data.
348 The ATtiny85 has a low-power mode which turns off all
349 of the clocks and powers down most of the internal
350 components. In this mode, the chip consumes only .1μA
351 of power. MicroPeak uses this mode once the flight has
352 ended to preserve battery power.
356 The CR1025 battery used by MicroPeak holds 30mAh of
357 power, which is sufficient to run for over 40
358 hours. Because MicroPeak powers down on landing, run
359 time includes only time sitting on the launch pad or
362 The large positive terminal (+) is usually marked,
363 while the smaller negative terminal is not. Make sure
364 you install the battery with the positive terminal
365 facing away from the circuit board where it will be in
366 contact with the metal battery holder. A small pad on
367 the circuit board makes contact with the negative
370 Shipping restrictions may prevent us from including a
371 CR1025 battery with MicroPeak. If so, many stores
372 carry CR1025 batteries as they are commonly used in
373 small electronic devices such as flash lights.
375 === Atmospheric Model
377 MicroPeak contains a fixed atmospheric model which is
378 used to convert barometric pressure into altitude. The
379 model was converted into a 469-element piece-wise
380 linear approximation which is then used to compute the
381 altitude of the ground and apogee. The difference
382 between these represents the maximum height of the
385 The model assumes a particular set of atmospheric
386 conditions, which, while a reasonable average, cannot
387 represent the changing nature of the real
388 atmosphere. Fortunately, for flights reasonably close
389 to the ground, the effect of this global inaccuracy
390 are largely canceled out when the computed ground
391 altitude is subtracted from the computed apogee
392 altitude, so the resulting height is more accurate
393 than either the ground or apogee altitudes.
395 Because the raw pressure data is recorded to
396 non-volatile storage, you can use that, along with a
397 more sophisticated atmospheric model, to compute your
400 === Mechanical Considerations
402 MicroPeak is designed to be rugged enough for typical
403 rocketry applications. It contains two moving parts,
404 the battery holder and the power switch, which were
405 selected for their ruggedness.
407 The MicroPeak battery holder is designed to withstand
408 impact up to 150g without breaking contact (or, worse
409 yet, causing the battery to fall out). That means it
410 should stand up to almost any launch you care to try,
411 and should withstand fairly rough landings.
413 The power switch is designed to withstand up to 50g
414 forces in any direction. Because it is a sliding
415 switch, orienting the switch perpendicular to the
416 direction of rocket travel will serve to further
417 protect the switch from launch forces.
419 === MicroPeak Programming Interface
421 MicroPeak exposes a standard 6-pin AVR programming
422 interface, but not using the usual 2x3 array of pins
423 on 0.1" centers. Instead, there is a single row of
424 tiny 0.60mm × 0.85mm pads on 1.20mm centers exposed
425 near the edge of the circuit board. We couldn't find
426 any connector that was small enough to include on the
429 In lieu of an actual connector, the easiest way to
430 connect to the bare pads is through a set of Pogo
431 pins. These spring-loaded contacts are designed to
432 connect in precisely this way. We've designed a
433 programming jig, the MicroPeak Pogo Pin board which
434 provides a standard AVR interface on one end and a
435 recessed slot for MicroPeak to align the board with
438 The MicroPeak Pogo Pin board is not a complete AVR
439 programmer, it is an interface board that provides a
440 3.3V regulated power supply to run the MicroPeak via
441 USB and a standard 6-pin AVR programming interface
442 with the usual 2x3 grid of pins on 0.1" centers. This
443 can be connected to any AVR programming dongle.
445 The AVR programming interface cannot run faster than ¼
446 of the AVR CPU clock frequency. Because MicroPeak runs
447 at 250kHz to save power, you must configure your AVR
448 programming system to clock the AVR programming
449 interface at no faster than 62.5kHz, or a clock period
453 == On-board data storage
455 The ATtiny85 has 512 bytes of non-volatile storage, separate
456 from the code storage memory. The MicroPeak firmware uses this
457 to store information about the last completed
458 flight. Barometric measurements from the ground before launch
459 and at apogee are stored, and used at power-on to compute the
460 height of the last flight.
462 In addition to the data used to present the height of the last
463 flight, MicroPeak also stores barometric information sampled
464 at regular intervals during the flight. This is the
465 information captured with the MicroPeak USB adapter. It can
466 also be read from MicroPeak through any AVR programming tool.
469 .MicroPeak EEPROM Data Storage
470 [options="border",cols="2,1,7"]
472 |Address |Size (bytes) |Description
473 |0x000 |4 |Average ground pressure (Pa)
474 |0x004 |4 |Minimum flight pressure (Pa)
475 |0x008 |2 |Number of in-flight samples
476 |0x00a … 0x1fe |2 |Instantaneous flight pressure (Pa) low 16 bits
479 All EEPROM data are stored least-significant byte first. The
480 instantaneous flight pressure data are stored without the
481 upper 16 bits of data. The upper bits can be reconstructed
482 from the previous sample, assuming that pressure doesn't
483 change by more more than 32kPa in a single sample
484 interval. Note that this pressure data is *not* filtered in
485 any way, while both the recorded ground and apogee pressure
486 values are, so you shouldn't expect the minimum instantaneous
487 pressure value to match the recorded minimum pressure value
490 MicroPeak samples pressure every 96ms, but stores only every
491 other sample in the EEPROM. This provides for 251 pressure
492 samples at 192ms intervals, or 48.192s of storage. The clock
493 used for these samples is a factory calibrated RC circuit
494 built into the ATtiny85 and is accurate only to within ±10% at
495 25°C. So, you can count on the pressure data being accurate,
496 but speed or acceleration data computed from this will be
497 limited by the accuracy of this clock.