1 <html><head><meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1"><title>MicroPeak Owner's Manual</title><meta name="generator" content="DocBook XSL Stylesheets V1.76.1"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="book" title="MicroPeak Owner's Manual"><div class="titlepage"><div><div><h1 class="title"><a name="idm14841928"></a>MicroPeak Owner's Manual</h1></div><div><h2 class="subtitle">A recording altimeter for hobby rocketry</h2></div><div><div class="author"><h3 class="author"><span class="firstname">Keith</span> <span class="surname">Packard</span></h3></div></div><div><p class="copyright">Copyright © 2012 Bdale Garbee and Keith Packard</p></div><div><div class="legalnotice" title="Legal Notice"><a name="idp108880"></a><p>
2 This document is released under the terms of the
3 <a class="ulink" href="http://creativecommons.org/licenses/by-sa/3.0/" target="_top">
4 Creative Commons ShareAlike 3.0
7 </p></div></div><div><div class="revhistory"><table border="1" width="100%" summary="Revision history"><tr><th align="left" valign="top" colspan="2"><b>Revision History</b></th></tr><tr><td align="left">Revision 0.1</td><td align="left">29 October 2012</td></tr><tr><td align="left" colspan="2">
8 Initial release with preliminary hardware.
9 </td></tr><tr><td align="left">Revision 1.0</td><td align="left">18 November 2012</td></tr><tr><td align="left" colspan="2">
10 Updates for version 1.0 release.
11 </td></tr><tr><td align="left">Revision 1.1</td><td align="left">12 December 2012</td></tr><tr><td align="left" colspan="2">
12 Add comments about EEPROM storage format and programming jig.
13 </td></tr><tr><td align="left">Revision 1.2</td><td align="left">20 January 2013</td></tr><tr><td align="left" colspan="2">
14 Add documentation for the MicroPeak USB adapter board. Note
15 the switch to a Kalman filter for peak altitude
17 </td></tr></table></div></div></div><hr></div><div class="acknowledgements" title="Acknowledgements"><div class="titlepage"><div><div><h2 class="title"><a name="idp772792"></a>Acknowledgements</h2></div></div></div>
19 Thanks to John Lyngdal for suggesting that we build something like this.
22 Have fun using these products, and we hope to meet all of you
23 out on the rocket flight line somewhere.
24 </p><div class="literallayout"><p><br>
25 Bdale Garbee, KB0G<br>
26 NAR #87103, TRA #12201<br>
28 Keith Packard, KD7SQG<br>
29 NAR #88757, TRA #12200<br>
32 </div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="chapter"><a href="#idp774040">1. Quick Start Guide</a></span></dt><dt><span class="chapter"><a href="#idp3062232">2. Handling Precautions</a></span></dt><dt><span class="chapter"><a href="#idp2529968">3. The MicroPeak USB adapter</a></span></dt><dd><dl><dt><span class="section"><a href="#idp2069328">1. Installing the MicroPeak software</a></span></dt><dt><span class="section"><a href="#idp1986896">2. Downloading Micro Peak data</a></span></dt><dt><span class="section"><a href="#idp3318344">3. Analyzing MicroPeak Data</a></span></dt><dt><span class="section"><a href="#idp785616">4. Configuring the MicroPeak application</a></span></dt></dl></dd><dt><span class="chapter"><a href="#idp3018560">4. Technical Information</a></span></dt><dd><dl><dt><span class="section"><a href="#idp3018880">1. Barometric Sensor</a></span></dt><dt><span class="section"><a href="#idp3020504">2. Micro-controller</a></span></dt><dt><span class="section"><a href="#idp3022056">3. Lithium Battery</a></span></dt><dt><span class="section"><a href="#idp3023856">4. Atmospheric Model</a></span></dt><dt><span class="section"><a href="#idp3025920">5. Mechanical Considerations</a></span></dt><dt><span class="section"><a href="#idp3027624">6. On-board data storage</a></span></dt><dt><span class="section"><a href="#idp52184">7. MicroPeak Programming Interface</a></span></dt></dl></dd></dl></div><div class="list-of-tables"><p><b>List of Tables</b></p><dl><dt>4.1. <a href="#idp3028936">MicroPeak EEPROM Data Storage</a></dt></dl></div><div class="chapter" title="Chapter 1. Quick Start Guide"><div class="titlepage"><div><div><h2 class="title"><a name="idp774040"></a>Chapter 1. Quick Start Guide</h2></div></div></div><p>
33 MicroPeak is designed to be easy to use. Requiring no external
34 components, flying takes just a few steps
35 </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
36 Install the battery. Fit a CR1025 battery into the plastic
37 carrier. The positive (+) terminal should be towards the more
38 open side of the carrier. Slip the carrier into the battery
39 holder with the positive (+) terminal facing away from the
41 </p></li><li class="listitem"><p>
42 Install MicroPeak in your rocket. This can be as simple as
43 preparing a soft cushion of wadding inside a vented model payload
44 bay. Wherever you mount it, make sure you protect the
45 barometric sensor from corrosive ejection gasses as those
46 will damage the sensor, and shield it from light as that can
47 cause incorrect sensor readings.
48 </p></li><li class="listitem"><p>
49 Turn MicroPeak on. Slide the switch so that the actuator
50 covers the '1' printed on the board. MicroPeak will report
51 the maximum height of the last flight in decimeters using a
52 sequence of flashes on the LED. A sequence of short flashes
53 indicates one digit. A single long flash indicates zero. The
54 height is reported in decimeters, so the last digit will be
55 tenths of a meter. For example, if MicroPeak reports 5 4 4
56 3, then the maximum height of the last flight was 544.3m, or
58 </p></li><li class="listitem"><p>
59 Finish preparing the rocket for flight. After the
60 previous flight data have been reported, MicroPeak waits for
61 30 seconds before starting to check for launch. This gives
62 you time to finish assembling the rocket. As those
63 activities might cause pressure changes inside the airframe,
64 MicroPeak might accidentally detect boost. If you need to do
65 anything to the airframe after the 30 second window passes,
66 make sure to be careful not to disturb the altimeter. The
67 LED will remain dark during the 30 second delay, but after
68 that, it will start blinking once every 3 seconds.
69 </p></li><li class="listitem"><p>
70 Fly the rocket. Once the rocket passes about 10m in height
71 (32 feet), the micro-controller will record the ground
72 pressure and track the pressure seen during the flight. In
73 this mode, the LED flickers rapidly. When the rocket lands,
74 and the pressure stabilizes, the micro-controller will record
75 the minimum pressure pressure experienced during the flight,
76 compute the height represented by the difference in air
77 pressure and blink that value out on the LED. After that,
78 MicroPeak powers down to conserve battery power.
79 </p></li><li class="listitem"><p>
80 Recover the data. Turn MicroPeak off and then back on. MicroPeak
81 will blink out the maximum height for the last flight. Turn
82 MicroPeak back off to conserve battery power.
83 </p></li></ul></div></div><div class="chapter" title="Chapter 2. Handling Precautions"><div class="titlepage"><div><div><h2 class="title"><a name="idp3062232"></a>Chapter 2. Handling Precautions</h2></div></div></div><p>
84 All Altus Metrum products are sophisticated electronic devices.
85 When handled gently and properly installed in an air-frame, they
86 will deliver impressive results. However, as with all electronic
87 devices, there are some precautions you must take.
89 The CR1025 Lithium batteries have an
90 extraordinary power density. This is great because we can fly with
91 much less battery mass... but if they are punctured
92 or their contacts are allowed to short, they can and will release their
94 Thus we recommend that you take some care when handling MicroPeak
95 to keep conductive material from coming in contact with the exposed metal elements.
97 The barometric sensor used in MicroPeak is sensitive to
98 sunlight. Please consider this when designing an
99 installation. Many model rockets with payload bays use clear
100 plastic for the payload bay. Replacing these with an opaque
101 cardboard tube, painting them, or wrapping them with a layer of
102 masking tape are all reasonable approaches to keep the sensor
103 out of direct sunlight.
105 The barometric sensor sampling ports must be able to "breathe",
106 both by not being covered by foam or tape or other materials that might
107 directly block the hole on the top of the sensor, and also by having a
108 suitable static vent to outside air.
110 As with all other rocketry electronics, Altus Metrum altimeters must
111 be protected from exposure to corrosive motor exhaust and ejection
113 </p></div><div class="chapter" title="Chapter 3. The MicroPeak USB adapter"><div class="titlepage"><div><div><h2 class="title"><a name="idp2529968"></a>Chapter 3. The MicroPeak USB adapter</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#idp2069328">1. Installing the MicroPeak software</a></span></dt><dt><span class="section"><a href="#idp1986896">2. Downloading Micro Peak data</a></span></dt><dt><span class="section"><a href="#idp3318344">3. Analyzing MicroPeak Data</a></span></dt><dt><span class="section"><a href="#idp785616">4. Configuring the MicroPeak application</a></span></dt></dl></div><p>
114 MicroPeak stores barometric pressure information for the first
115 48 seconds of the flight in on-board non-volatile memory. The
116 contents of this memory can be downloaded to a computer using
117 the MicroPeak USB adapter.
118 </p><div class="section" title="1. Installing the MicroPeak software"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp2069328"></a>1. Installing the MicroPeak software</h2></div></div></div><p>
119 The MicroPeak application runs on Linux, Mac OS X and
120 Windows. You can download the latest version from
121 <a class="ulink" href="http://altusmetrum.org/AltOS" target="_top">http://altusmetrum.org/AltOS</a>.
123 On Mac OS X and Windows, the FTDI USB device driver needs to
124 be installed. A compatible version of this driver is included
125 with the MicroPeak application, but you may want to download a
126 newer version from <a class="ulink" href="http://www.ftdichip.com/FTDrivers.htm" target="_top">http://www.ftdichip.com/FTDrivers.htm</a>.
127 </p></div><div class="section" title="2. Downloading Micro Peak data"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp1986896"></a>2. Downloading Micro Peak data</h2></div></div></div><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
128 Connect the MicroPeak USB adapter to a USB cable and plug it
130 </p></li><li class="listitem"><p>
131 Start the MicroPeak application, locate the File menu and
132 select the Download entry.
133 </p></li><li class="listitem"><p>
134 The MicroPeak USB adapter has a small phototransistor on the
135 end of the board furthest from the USB connector. Locate
136 this and place the LED on the MicroPeak right over
137 it. Turn on the MicroPeak board and adjust the position
138 until the blue LED on the MicroPeak USB adapter blinks in
139 time with the orange LED on the MicroPeak board.
140 </p></li><li class="listitem"><p>
141 After the maximum flight height is reported, MicroPeak will
142 pause for a few seconds, blink the LED four times rapidly
143 and then send the data in one long blur on the LED. The
144 MicroPeak application should receive the data. When it does,
145 it will present the data in a graph and offer to save the
146 data to a file. If not, you can power cycle the MicroPeak
148 </p></li></ul></div></div><div class="section" title="3. Analyzing MicroPeak Data"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp3318344"></a>3. Analyzing MicroPeak Data</h2></div></div></div><p>
149 The MicroPeak application can present flight data in the form
150 of a graph, a collection of computed statistics or in tabular
153 MicroPeak collects raw barometric pressure data which is
154 then used to compute the remaining data. Altitude is computed
155 through a standard atmospheric model. Absolute error in this
156 data will be affected by local atmospheric
157 conditions. Fortunately, these errors tend to mostly cancel
158 out, so the error in the height computation is much smaller
159 than the error in altitude would be.
161 Speed and acceleration are computed by first smoothing the
162 height data with a Gaussian window averaging filter. For speed
163 data, this average uses seven samples. For acceleration data,
164 eleven samples are used. These were chosen to provide
165 reasonably smooth speed and acceleration data, which would
166 otherwise be swamped with noise.
168 Under the Graph tab, the height, speed and acceleration values
169 are displayed together. You can zoom in on the graph by
170 clicking and dragging to sweep out an area of
171 interest. Right-click on the plot to bring up a menu that will
172 let you save, copy or print the graph.
174 The Statistics tab presents overall data from the flight. Note
175 that the Maximum height value is taken from the minumum
176 pressure captured in flight, and may be different from the
177 apparant apogee value as the on-board data are sampled twice
178 as fast as the recorded values, or because the true apogee
179 occurred after the on-board memory was full. Each value is
180 presented in several units as appropriate.
182 A table consisting of the both the raw barometric pressure
183 data and values computed from that for each recorded time.
185 The File menu has operations to open existing flight logs,
186 Download new data from MicroPeak, Save a copy of the flight
187 log to a new file, Export the tabular data (as seen in the Raw
188 Data tab) to a file, change the application Preferences, Close
189 the current window or close all windows and Exit the
191 </p></div><div class="section" title="4. Configuring the MicroPeak application"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp785616"></a>4. Configuring the MicroPeak application</h2></div></div></div><p>
192 The MicroPeak application has a few user settings which are
193 configured through the Preferences dialog, which can be
194 accessed from the File menu.
195 </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
196 The Log Directory is where flight data will be saved to
197 and loaded from by default. Of course, you can always
198 navigate to other directories in the file chooser windows,
199 this setting is just the starting point.
200 </p></li><li class="listitem"><p>
201 If you prefer to see your graph data in feet and
202 miles per hour instead of meters and meters per second,
203 you can select Imperial Units.
204 </p></li><li class="listitem"><p>
205 To see what data is actually arriving over the serial
206 port, start the MicroPeak application from a command
207 prompt and select the Serial Debug option. This can be
208 useful in debugging serial communication problems, but
209 most people need never choose this.
210 </p></li><li class="listitem"><p>
211 You can adjust the size of the text in the Statistics tab
212 by changing the Font size preference. There are three
213 settings, with luck one will both fit on your screen and
214 provide readable values.
215 </p></li><li class="listitem"><p>
216 The Look & feel menu shows a list of available
217 application appearance choices. By default, the MicroPeak
218 application tries to blend in with other applications, but
219 you may choose some other appearance if you like.
220 </p></li></ul></div><p>
222 Note that MicroPeak shares a subset of the AltosUI
223 preferences, so if you use both of these applications, change
224 in one application will affect the other.
225 </p></div></div><div class="chapter" title="Chapter 4. Technical Information"><div class="titlepage"><div><div><h2 class="title"><a name="idp3018560"></a>Chapter 4. Technical Information</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#idp3018880">1. Barometric Sensor</a></span></dt><dt><span class="section"><a href="#idp3020504">2. Micro-controller</a></span></dt><dt><span class="section"><a href="#idp3022056">3. Lithium Battery</a></span></dt><dt><span class="section"><a href="#idp3023856">4. Atmospheric Model</a></span></dt><dt><span class="section"><a href="#idp3025920">5. Mechanical Considerations</a></span></dt><dt><span class="section"><a href="#idp3027624">6. On-board data storage</a></span></dt><dt><span class="section"><a href="#idp52184">7. MicroPeak Programming Interface</a></span></dt></dl></div><div class="section" title="1. Barometric Sensor"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp3018880"></a>1. Barometric Sensor</h2></div></div></div><p>
226 MicroPeak uses the Measurement Specialties MS5607 sensor. This
227 has a range of 120kPa to 1kPa with an absolute accuracy of
228 150Pa and a resolution of 2.4Pa.
230 The pressure range corresponds roughly to an altitude range of
231 -1500m (-4900 feet) to 31000m (102000 feet), while the
232 resolution is approximately 20cm (8 inches) near sea level and
233 60cm (24in) at 10000m (33000 feet).
235 Ground pressure is computed from an average of 16 samples,
236 taken while the altimeter is at rest. Flight pressure is
237 computed from a Kalman filter designed to smooth out any minor
238 noise in the sensor values.
239 </p></div><div class="section" title="2. Micro-controller"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp3020504"></a>2. Micro-controller</h2></div></div></div><p>
240 MicroPeak uses an Atmel ATtiny85 micro-controller. This tiny
241 CPU contains 8kB of flash for the application, 512B of RAM for
242 temporary data storage and 512B of EEPROM for non-volatile
243 storage of previous flight data.
245 The ATtiny85 has a low-power mode which turns off all of the
246 clocks and powers down most of the internal components. In
247 this mode, the chip consumes only .1μA of power. MicroPeak
248 uses this mode once the flight has ended to preserve battery
250 </p></div><div class="section" title="3. Lithium Battery"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp3022056"></a>3. Lithium Battery</h2></div></div></div><p>
251 The CR1025 battery used by MicroPeak holes 30mAh of power,
252 which is sufficient to run for over 40 hours. Because
253 MicroPeak powers down on landing, run time includes only time
254 sitting on the launch pad or during flight.
256 The large positive terminal (+) is usually marked, while the
257 smaller negative terminal is not. Make sure you install the
258 battery with the positive terminal facing away from the
259 circuit board where it will be in contact with the metal
260 battery holder. A small pad on the circuit board makes contact
261 with the negative battery terminal.
263 Shipping restrictions may prevent us from including a CR1025
264 battery with MicroPeak. If so, many stores carry CR1025
265 batteries as they are commonly used in small electronic
266 devices such as flash lights.
267 </p></div><div class="section" title="4. Atmospheric Model"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp3023856"></a>4. Atmospheric Model</h2></div></div></div><p>
268 MicroPeak contains a fixed atmospheric model which is used to
269 convert barometric pressure into altitude. The model was
270 converted into a 469-element piece wise linear approximation
271 which is then used to compute the altitude of the ground and
272 apogee. The difference between these represents the maximum
273 height of the flight.
275 The model assumes a particular set of atmospheric conditions,
276 which while a reasonable average cannot represent the changing
277 nature of the real atmosphere. Fortunately, for flights
278 reasonably close to the ground, the effect of this global
279 inaccuracy are largely canceled out when the computed ground
280 altitude is subtracted from the computed apogee altitude, so
281 the resulting height is more accurate than either the ground
283 </p></div><div class="section" title="5. Mechanical Considerations"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp3025920"></a>5. Mechanical Considerations</h2></div></div></div><p>
284 MicroPeak is designed to be rugged enough for typical rocketry
285 applications. It contains two moving parts, the battery holder
286 and the power switch, which were selected for their
289 The MicroPeak battery holder is designed to withstand impact
290 up to 150g without breaking contact (or, worse yet, causing
291 the battery to fall out). That means it should stand up to
292 almost any launch you care to try, and should withstand fairly
295 The power switch is designed to withstand up to 50g forces in
296 any direction. Because it is a sliding switch, orienting the
297 switch perpendicular to the direction of rocket travel will
298 serve to further protect the switch from launch forces.
299 </p></div><div class="section" title="6. On-board data storage"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp3027624"></a>6. On-board data storage</h2></div></div></div><p>
300 The ATtiny85 has 512 bytes of non-volatile storage, separate
301 from the code storage memory. The MicroPeak firmware uses this
302 to store information about the last completed
303 flight. Barometric measurements from the ground before launch
304 and at apogee are stored, and used at power-on to compute the
305 height of the last flight.
307 In addition to the data used to present the height of the last
308 flight, MicroPeak also stores barometric information sampled
309 at regular intervals during the flight. This information can
310 be extracted from MicroPeak through any AVR programming
312 </p><div class="table"><a name="idp3028936"></a><p class="title"><b>Table 4.1. MicroPeak EEPROM Data Storage</b></p><div class="table-contents"><table summary="MicroPeak EEPROM Data Storage" border="1"><colgroup><col align="center" class="Address"><col align="center" class="Size (bytes)"><col align="left" class="Description"></colgroup><thead><tr><th align="center">Address</th><th align="center">Size (bytes)</th><th align="center">Description</th></tr></thead><tbody><tr><td align="center">0x000</td><td align="center">4</td><td align="left">Average ground pressure (Pa)</td></tr><tr><td align="center">0x004</td><td align="center">4</td><td align="left">Minimum flight pressure (Pa)</td></tr><tr><td align="center">0x008</td><td align="center">2</td><td align="left">Number of in-flight samples</td></tr><tr><td align="center">0x00a … 0x1fe</td><td align="center">2</td><td align="left">Instantaneous flight pressure (Pa) low 16 bits</td></tr></tbody></table></div></div><br class="table-break"><p>
313 All EEPROM data are stored least-significant byte first. The
314 instantaneous flight pressure data are stored without the
315 upper 16 bits of data. The upper bits can be reconstructed
316 from the previous sample, assuming that pressure doesn't
317 change by more more than 32kPa in a single sample
318 interval. Note that this pressure data is <span class="emphasis"><em>not</em></span>
319 filtered in any way, while both the recorded ground and apogee
320 pressure values are, so you shouldn't expect the minimum
321 instantaneous pressure value to match the recorded minimum
322 pressure value exactly.
324 MicroPeak samples pressure every 96ms, but stores only every
325 other sample in the EEPROM. This provides for 251 pressure
326 samples at 192ms intervals, or 48.192s of storage. The clock
327 used for these samples is a factory calibrated RC circuit
328 built into the ATtiny85 and is accurate only to within ±10% at
329 25°C. So, you can count on the pressure data being accurate,
330 but speed or acceleration data computed from this will be
331 limited by the accuracy of this clock.
332 </p></div><div class="section" title="7. MicroPeak Programming Interface"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp52184"></a>7. MicroPeak Programming Interface</h2></div></div></div><p>
333 MicroPeak exposes a standard 6-pin AVR programming interface,
334 but not using the usual 2x3 array of pins on 0.1"
335 centers. Instead, there is a single row of tiny 0.60mm ×
336 0.85mm pads on 1.20mm centers exposed near the edge of the
337 circuit board. We couldn't find any connector that was
338 small enough to include on the circuit board.
340 In lieu of an actual connector, the easiest way to connect to
341 the bare pads is through a set of Pogo pins. These
342 spring-loaded contacts are designed to connect in precisely
343 this way. We've designed a programming jig, the MicroPeak
344 Pogo Pin board which provides a standard AVR interface on one
345 end and a recessed slot for MicroPeak to align the board with
348 The MicroPeak Pogo Pin board is not a complete AVR programmer,
349 it is an interface board that provides a 3.3V regulated power
350 supply to run the MicroPeak via USB and a standard 6-pin AVR
351 programming interface with the usual 2x3 grid of pins on 0.1"
352 centers. This can be connected to any AVR programming
355 The AVR programming interface cannot run faster than ¼ of the
356 AVR CPU clock frequency. Because MicroPeak runs at 250kHz to
357 save power, you must configure your AVR programming system to
358 clock the AVR programming interface at no faster than
359 62.5kHz, or a clock period of 32µS.
360 </p></div></div></div></body></html>
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