1 = MicroPeak Owner's Manual
2 Keith Packard <keithp@keithp.com>; Bdale Garbee <bdale@gag.com>
5 :copyright: Bdale Garbee and Keith Packard 2018
12 :pdf-style: altusmetrum
15 include::header.adoc[]
20 Thanks to John Lyngdal for suggesting that we build something
23 Have fun using these products, and we hope to meet all of you
24 out on the rocket flight line somewhere.
28 NAR #87103, TRA #12201
32 NAR #88757, TRA #12200
36 MicroPeak is designed to be easy to use. Requiring no external
37 components, flying takes just a few steps
41 Fit a CR1025 battery into the plastic carrier. The positive
42 (\+) terminal should be towards the more open side of the
43 carrier. Slip the carrier into the battery holder with the
44 positive (+) terminal facing away from the circuit board.
46 .MicroPeak and Battery
47 image::micropeak-back.jpg[width=430]
49 Install MicroPeak in your rocket::
51 This can be as simple as preparing a soft cushion of wadding
52 inside a vented model payload bay. Wherever you mount it,
53 make sure you protect the barometric sensor from corrosive
54 ejection gasses as those will damage the sensor, and shield
55 it from light as that can cause incorrect sensor readings.
59 Slide the switch so that the actuator covers the '1' printed
60 on the board. MicroPeak will report the maximum height of
61 the last flight in decimeters using a sequence of flashes on
62 the LED. A sequence of short flashes indicates one digit. A
63 single long flash indicates zero. The height is reported in
64 decimeters, so the last digit will be tenths of a meter. For
65 example, if MicroPeak reports 5 4 4 3, then the maximum
66 height of the last flight was 544.3m, or 1786 feet.
68 Finish preparing the rocket for flight::
70 After the previous flight data have been reported, MicroPeak
71 waits for one minute before starting to check for
72 launch. This gives you time to finish assembling the
73 rocket. As those activities might cause pressure changes
74 inside the airframe, MicroPeak might accidentally detect
75 boost. If you need to do anything to the airframe after the
76 one minute window passes, make sure to be careful not to
77 disturb the altimeter. The LED will remain dark during the
78 one minute delay, but after that, it will start blinking
83 Once the rocket passes about 30m in height (100 feet), the
84 micro-controller will record the ground pressure and track
85 the pressure seen during the flight. In this mode, the LED
86 flickers rapidly. When the rocket lands, and the pressure
87 stabilizes, the micro-controller will record the minimum
88 pressure pressure experienced during the flight, compute the
89 height represented by the difference in air pressure and
90 blink that value out on the LED. After that, MicroPeak
91 powers down to conserve battery power.
95 Turn MicroPeak off and then back on. MicroPeak will blink
96 out the maximum height for the last flight. Turn MicroPeak
97 back off to conserve battery power.
99 == The MicroPeak USB adapter
101 .MicroPeak USB Adapter
102 image::MicroPeakUSB-2.0.jpg[width=430,align="center"]
104 MicroPeak stores barometric pressure information for the first
105 48 seconds of the flight in on-board non-volatile memory. The
106 contents of this memory can be downloaded to a computer using
107 the MicroPeak USB adapter.
109 === Installing the MicroPeak software
111 The MicroPeak application runs on Linux, Mac OS X and
112 Windows. You can download the latest version from
113 http://altusmetrum.org/MicroPeak
115 On Mac OS X and Windows, the FTDI USB device driver
116 needs to be installed. A compatible version of this
117 driver is included with the MicroPeak application, but
118 you may want to download a newer version from
119 http://www.ftdichip.com/FTDrivers.htm
121 === Downloading Micro Peak data
123 * Plug the MicroPeak USB adapter in to your computer.
125 * Start the MicroPeak application.
127 image::micropeak-nofont.svg[width=50,align="center"]
129 * Click on the Download button at the top of the
132 .MicroPeak Application
133 image::micropeak-app.png[width=430,align="center"]
135 * Select from the listed devices. There will probably
138 .MicroPeak Device Dialog
139 image::micropeak-device-dialog.png[width=220,align="center"]
141 * The application will now wait until it receives
142 valid data from the MicroPeak USB adapter.
144 .MicroPeak Download Dialog
145 image::micropeak-download.png[width=200,align="center"]
147 * The MicroPeak USB adapter has a small
148 phototransistor under the hole in the center of the
149 box. Locate this, turn on the MicroPeak and place
150 the orange LED on the MicroPeak directly inside the
151 hole, resting the MicroPeak itself on the box. You
152 should see the blue LED on the MicroPeak USB adapter
153 blinking in time with the orange LED on the
154 MicroPeak board itself.
156 .MicroPeak Downloading
157 image::MicroPeakUSB-2.0-inuse.jpg[width=430,align="center"]
159 * After the maximum flight height is reported,
160 MicroPeak will pause for a few seconds, blink the
161 LED four times rapidly and then send the data in one
162 long blur on the LED. The MicroPeak application
163 should receive the data. When it does, it will
164 present the data in a graph and offer to save the
165 data to a file. If not, you can power cycle the
166 MicroPeak board and try again.
168 .MicroPeak Save Dialog
169 image::micropeak-save-dialog.png[width=220,align="center"]
171 * Once the data are saved, a graph will be displayed
172 with height, speed and acceleration values computed
173 from the recorded barometric pressure data. See
174 <<_analyzing_micropeak_data> for more details on that.
176 === Analyzing MicroPeak Data
178 The MicroPeak application can present flight data in
179 the form of a graph, a collection of computed
180 statistics or in tabular form.
182 MicroPeak collects raw barometric pressure data which
183 is then used to compute the remaining data. Altitude
184 is computed through a standard atmospheric
185 model. Absolute error in this data will be affected by
186 local atmospheric conditions. Fortunately, these
187 errors tend to mostly cancel out, so the error in the
188 height computation is much smaller than the error in
191 Speed and acceleration are computed by first smoothing
192 the height data with a Gaussian window averaging
193 filter. For speed data, this average uses seven
194 samples. For acceleration data, eleven samples are
195 used. These were chosen to provide reasonably smooth
196 speed and acceleration data, which would otherwise be
199 The File menu has operations to open existing flight
200 logs, Download new data from MicroPeak, Save a copy of
201 the flight log to a new file, Export the tabular data
202 (as seen in the Raw Data tab) to a file, change the
203 application Preferences, Close the current window or
204 close all windows and Exit the application.
206 ==== MicroPeak Graphs
209 image::micropeak-graph.png[width=430,align="center"]
211 Under the Graph tab, the height, speed and acceleration values
212 are displayed together. You can zoom in on the graph by
213 clicking and dragging to sweep out an area of
214 interest. Right-click on the plot to bring up a menu that will
215 let you save, copy or print the graph.
217 ==== MicroPeak Flight Statistics
219 .MicroPeak Flight Statistics
220 image::micropeak-statistics.png[width=430,align="center"]
222 The Statistics tab presents overall data from
223 the flight. Note that the Maximum height value
224 is taken from the minumum pressure captured in
225 flight, and may be different from the apparant
226 apogee value as the on-board data are sampled
227 twice as fast as the recorded values, or
228 because the true apogee occurred after the
229 on-board memory was full. Each value is
230 presented in several units as appropriate.
234 .MicroPeak Raw Flight Data
235 image::micropeak-raw-data.png[width=430,align="center"]
237 A table consisting of the both the raw barometric pressure
238 data and values computed from that for each recorded time.
240 ==== Configuring the Graph
242 .MicroPeak Graph Configuration
243 image::micropeak-graph-configure.png[width=430,align="center"]
245 This selects which graph elements to show, and lets you
246 switch between metric and imperial units
248 === Setting MicroPeak Preferences
250 .MicroPeak Preferences
251 image::micropeak-preferences.png[width=170,align="center"]
253 The MicroPeak application has a few user settings which are
254 configured through the Preferences dialog, which can be
255 accessed from the File menu.
259 The Log Directory is where flight data will be
260 saved to and loaded from by default. Of
261 course, you can always navigate to other
262 directories in the file chooser windows, this
263 setting is just the starting point.
267 If you prefer to see your graph data in feet
268 and miles per hour instead of meters and
269 meters per second, you can select Imperial
274 To see what data is actually arriving over the
275 serial port, start the MicroPeak application
276 from a command prompt and select the Serial
277 Debug option. This can be useful in debugging
278 serial communication problems, but most people
279 need never choose this.
283 You can adjust the size of the text in the
284 Statistics tab by changing the Font size
285 preference. There are three settings, with
286 luck one will both fit on your screen and
287 provide readable values.
291 The Look & feel menu shows a list of available
292 application appearance choices. By default,
293 the MicroPeak application tries to blend in
294 with other applications, but you may choose
295 some other appearance if you like.
297 Note that MicroPeak shares a subset of the
298 AltosUI preferences, so if you use both of
299 these applications, change in one application
300 will affect the other.
303 == Handling Precautions
305 All Altus Metrum products are sophisticated electronic
306 devices. When handled gently and properly installed in an
307 air-frame, they will deliver impressive results. However, as
308 with all electronic devices, there are some precautions you
313 The CR1025 Lithium batteries have an extraordinary power
314 density. This is great because we can fly with much less
315 battery mass... but if they are punctured or their contacts
316 are allowed to short, they can and will release their energy
317 very rapidly! Thus we recommend that you take some care when
318 handling MicroPeak to keep conductive material from coming in
319 contact with the exposed metal elements.
321 The barometric sensor used in MicroPeak is sensitive to
322 sunlight. Please consider this when designing an
323 installation. Many model rockets with payload bays use clear
324 plastic for the payload bay. Replacing these with an opaque
325 cardboard tube, painting them, or wrapping them with a layer
326 of masking tape are all reasonable approaches to keep the
327 sensor out of direct sunlight.
329 The barometric sensor sampling ports must be able to
330 "breathe", both by not being covered by foam or tape or other
331 materials that might directly block the hole on the top of the
332 sensor, and also by having a suitable static vent to outside
335 As with all other rocketry electronics, Altus Metrum
336 altimeters must be protected from exposure to corrosive motor
337 exhaust and ejection charge gasses.
340 == Technical Information
342 === Barometric Sensor
344 MicroPeak uses the Measurement Specialties MS5607
345 sensor. This has a range of 120kPa to 1kPa with an
346 absolute accuracy of 150Pa and a resolution of 2.4Pa.
348 The pressure range corresponds roughly to an altitude
349 range of -1500m (-4900 feet) to 31000m (102000 feet),
350 while the resolution is approximately 20cm (8 inches)
351 near sea level and 60cm (24in) at 10000m (33000 feet).
353 Ground pressure is computed from an average of 16
354 samples, taken while the altimeter is at rest. The
355 flight pressure used to report maximum height is
356 computed from a Kalman filter designed to smooth out
357 any minor noise in the sensor values. The flight
358 pressure recorded to non-volatile storage is
359 unfiltered, coming directly from the pressure sensor.
363 MicroPeak uses an Atmel ATtiny85
364 micro-controller. This tiny CPU contains 8kB of flash
365 for the application, 512B of RAM for temporary data
366 storage and 512B of EEPROM for non-volatile storage of
367 previous flight data.
369 The ATtiny85 has a low-power mode which turns off all
370 of the clocks and powers down most of the internal
371 components. In this mode, the chip consumes only .1μA
372 of power. MicroPeak uses this mode once the flight has
373 ended to preserve battery power.
377 The CR1025 battery used by MicroPeak holds 30mAh of
378 power, which is sufficient to run for over 40
379 hours. Because MicroPeak powers down on landing, run
380 time includes only time sitting on the launch pad or
383 The large positive terminal (+) is usually marked,
384 while the smaller negative terminal is not. Make sure
385 you install the battery with the positive terminal
386 facing away from the circuit board where it will be in
387 contact with the metal battery holder. A small pad on
388 the circuit board makes contact with the negative
391 Shipping restrictions may prevent us from including a
392 CR1025 battery with MicroPeak. If so, many stores
393 carry CR1025 batteries as they are commonly used in
394 small electronic devices such as flash lights.
396 === Atmospheric Model
398 MicroPeak contains a fixed atmospheric model which is
399 used to convert barometric pressure into altitude. The
400 model was converted into a 469-element piece-wise
401 linear approximation which is then used to compute the
402 altitude of the ground and apogee. The difference
403 between these represents the maximum height of the
406 The model assumes a particular set of atmospheric
407 conditions, which, while a reasonable average, cannot
408 represent the changing nature of the real
409 atmosphere. Fortunately, for flights reasonably close
410 to the ground, the effect of this global inaccuracy
411 are largely canceled out when the computed ground
412 altitude is subtracted from the computed apogee
413 altitude, so the resulting height is more accurate
414 than either the ground or apogee altitudes.
416 Because the raw pressure data is recorded to
417 non-volatile storage, you can use that, along with a
418 more sophisticated atmospheric model, to compute your
421 === Mechanical Considerations
423 MicroPeak is designed to be rugged enough for typical
424 rocketry applications. It contains two moving parts,
425 the battery holder and the power switch, which were
426 selected for their ruggedness.
428 The MicroPeak battery holder is designed to withstand
429 impact up to 150g without breaking contact (or, worse
430 yet, causing the battery to fall out). That means it
431 should stand up to almost any launch you care to try,
432 and should withstand fairly rough landings.
434 The power switch is designed to withstand up to 50g
435 forces in any direction. Because it is a sliding
436 switch, orienting the switch perpendicular to the
437 direction of rocket travel will serve to further
438 protect the switch from launch forces.
440 === MicroPeak Programming Interface
442 MicroPeak exposes a standard 6-pin AVR programming
443 interface, but not using the usual 2x3 array of pins
444 on 0.1" centers. Instead, there is a single row of
445 tiny 0.60mm × 0.85mm pads on 1.20mm centers exposed
446 near the edge of the circuit board. We couldn't find
447 any connector that was small enough to include on the
450 In lieu of an actual connector, the easiest way to
451 connect to the bare pads is through a set of Pogo
452 pins. These spring-loaded contacts are designed to
453 connect in precisely this way. We've designed a
454 programming jig, the MicroPeak Pogo Pin board which
455 provides a standard AVR interface on one end and a
456 recessed slot for MicroPeak to align the board with
459 The MicroPeak Pogo Pin board is not a complete AVR
460 programmer, it is an interface board that provides a
461 3.3V regulated power supply to run the MicroPeak via
462 USB and a standard 6-pin AVR programming interface
463 with the usual 2x3 grid of pins on 0.1" centers. This
464 can be connected to any AVR programming dongle.
466 The AVR programming interface cannot run faster than ¼
467 of the AVR CPU clock frequency. Because MicroPeak runs
468 at 250kHz to save power, you must configure your AVR
469 programming system to clock the AVR programming
470 interface at no faster than 62.5kHz, or a clock period
474 == On-board data storage
476 The ATtiny85 has 512 bytes of non-volatile storage, separate
477 from the code storage memory. The MicroPeak firmware uses this
478 to store information about the last completed
479 flight. Barometric measurements from the ground before launch
480 and at apogee are stored, and used at power-on to compute the
481 height of the last flight.
483 In addition to the data used to present the height of the last
484 flight, MicroPeak also stores barometric information sampled
485 at regular intervals during the flight. This is the
486 information captured with the MicroPeak USB adapter. It can
487 also be read from MicroPeak through any AVR programming tool.
490 .MicroPeak EEPROM Data Storage
491 [options="border",cols="2,1,7"]
493 |Address |Size (bytes) |Description
494 |0x000 |4 |Average ground pressure (Pa)
495 |0x004 |4 |Minimum flight pressure (Pa)
496 |0x008 |2 |Number of in-flight samples
497 |0x00a … 0x1fe |2 |Instantaneous flight pressure (Pa) low 16 bits
500 All EEPROM data are stored least-significant byte first. The
501 instantaneous flight pressure data are stored without the
502 upper 16 bits of data. The upper bits can be reconstructed
503 from the previous sample, assuming that pressure doesn't
504 change by more more than 32kPa in a single sample
505 interval. Note that this pressure data is *not* filtered in
506 any way, while both the recorded ground and apogee pressure
507 values are, so you shouldn't expect the minimum instantaneous
508 pressure value to match the recorded minimum pressure value
511 MicroPeak samples pressure every 96ms, but stores only every
512 other sample in the EEPROM. This provides for 251 pressure
513 samples at 192ms intervals, or 48.192s of storage. The clock
514 used for these samples is a factory calibrated RC circuit
515 built into the ATtiny85 and is accurate only to within ±10% at
516 25°C. So, you can count on the pressure data being accurate,
517 but speed or acceleration data computed from this will be
518 limited by the accuracy of this clock.