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 V1.78.1"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><div class="book"><div class="titlepage"><div><div><h1 class="title"><a name="idm6245264"></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"><a name="idp48058064"></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 style="border-style:solid; 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="dedication"><div class="titlepage"><div><div><h1 class="title"><a name="idp47885280"></a>Acknowledgements</h1></div></div></div><p>
18 Thanks to John Lyngdal for suggesting that we build something like this.
20 Have fun using these products, and we hope to meet all of you
21 out on the rocket flight line somewhere.
22 </p><div class="literallayout"><p><br>
23 Bdale Garbee, KB0G<br>
24 NAR #87103, TRA #12201<br>
26 Keith Packard, KD7SQG<br>
27 NAR #88757, TRA #12200<br>
29 </p></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="chapter"><a href="#idp48960176">1. Quick Start Guide</a></span></dt><dt><span class="chapter"><a href="#idp48969664">2. Handling Precautions</a></span></dt><dt><span class="chapter"><a href="#idp53493376">3. The MicroPeak USB adapter</a></span></dt><dd><dl><dt><span class="section"><a href="#idp53494704">1. Installing the MicroPeak software</a></span></dt><dt><span class="section"><a href="#idp53497792">2. Downloading Micro Peak data</a></span></dt><dt><span class="section"><a href="#idp53503952">3. Analyzing MicroPeak Data</a></span></dt><dt><span class="section"><a href="#idp47886320">4. Configuring the MicroPeak application</a></span></dt></dl></dd><dt><span class="chapter"><a href="#idp47894112">4. Technical Information</a></span></dt><dd><dl><dt><span class="section"><a href="#idp47894784">1. Barometric Sensor</a></span></dt><dt><span class="section"><a href="#idp47897392">2. Micro-controller</a></span></dt><dt><span class="section"><a href="#idp47899744">3. Lithium Battery</a></span></dt><dt><span class="section"><a href="#idp47902528">4. Atmospheric Model</a></span></dt><dt><span class="section"><a href="#idp47904928">5. Mechanical Considerations</a></span></dt><dt><span class="section"><a href="#idp47907680">6. On-board data storage</a></span></dt><dt><span class="section"><a href="#idp54636384">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="#idp47909744">MicroPeak EEPROM Data Storage</a></dt></dl></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="idp48960176"></a>Chapter 1. Quick Start Guide</h1></div></div></div><p>
30 MicroPeak is designed to be easy to use. Requiring no external
31 components, flying takes just a few steps
32 </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
33 Install the battery. Fit a CR1025 battery into the plastic
34 carrier. The positive (+) terminal should be towards the more
35 open side of the carrier. Slip the carrier into the battery
36 holder with the positive (+) terminal facing away from the
38 </p></li><li class="listitem"><p>
39 Install MicroPeak in your rocket. This can be as simple as
40 preparing a soft cushion of wadding inside a vented model payload
41 bay. Wherever you mount it, make sure you protect the
42 barometric sensor from corrosive ejection gasses as those
43 will damage the sensor, and shield it from light as that can
44 cause incorrect sensor readings.
45 </p></li><li class="listitem"><p>
46 Turn MicroPeak on. Slide the switch so that the actuator
47 covers the '1' printed on the board. MicroPeak will report
48 the maximum height of the last flight in decimeters using a
49 sequence of flashes on the LED. A sequence of short flashes
50 indicates one digit. A single long flash indicates zero. The
51 height is reported in decimeters, so the last digit will be
52 tenths of a meter. For example, if MicroPeak reports 5 4 4
53 3, then the maximum height of the last flight was 544.3m, or
55 </p></li><li class="listitem"><p>
56 Finish preparing the rocket for flight. After the
57 previous flight data have been reported, MicroPeak waits for
58 one minute before starting to check for launch. This gives
59 you time to finish assembling the rocket. As those
60 activities might cause pressure changes inside the airframe,
61 MicroPeak might accidentally detect boost. If you need to do
62 anything to the airframe after the one minute window passes,
63 make sure to be careful not to disturb the altimeter. The
64 LED will remain dark during the one minute delay, but after
65 that, it will start blinking once every 3 seconds.
66 </p></li><li class="listitem"><p>
67 Fly the rocket. Once the rocket passes about 30m in height
68 (100 feet), the micro-controller will record the ground
69 pressure and track the pressure seen during the flight. In
70 this mode, the LED flickers rapidly. When the rocket lands,
71 and the pressure stabilizes, the micro-controller will record
72 the minimum pressure pressure experienced during the flight,
73 compute the height represented by the difference in air
74 pressure and blink that value out on the LED. After that,
75 MicroPeak powers down to conserve battery power.
76 </p></li><li class="listitem"><p>
77 Recover the data. Turn MicroPeak off and then back on. MicroPeak
78 will blink out the maximum height for the last flight. Turn
79 MicroPeak back off to conserve battery power.
80 </p></li></ul></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="idp48969664"></a>Chapter 2. Handling Precautions</h1></div></div></div><p>
81 All Altus Metrum products are sophisticated electronic devices.
82 When handled gently and properly installed in an air-frame, they
83 will deliver impressive results. However, as with all electronic
84 devices, there are some precautions you must take.
86 The CR1025 Lithium batteries have an
87 extraordinary power density. This is great because we can fly with
88 much less battery mass... but if they are punctured
89 or their contacts are allowed to short, they can and will release their
91 Thus we recommend that you take some care when handling MicroPeak
92 to keep conductive material from coming in contact with the exposed metal elements.
94 The barometric sensor used in MicroPeak is sensitive to
95 sunlight. Please consider this when designing an
96 installation. Many model rockets with payload bays use clear
97 plastic for the payload bay. Replacing these with an opaque
98 cardboard tube, painting them, or wrapping them with a layer of
99 masking tape are all reasonable approaches to keep the sensor
100 out of direct sunlight.
102 The barometric sensor sampling ports must be able to "breathe",
103 both by not being covered by foam or tape or other materials that might
104 directly block the hole on the top of the sensor, and also by having a
105 suitable static vent to outside air.
107 As with all other rocketry electronics, Altus Metrum altimeters must
108 be protected from exposure to corrosive motor exhaust and ejection
110 </p></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="idp53493376"></a>Chapter 3. The MicroPeak USB adapter</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#idp53494704">1. Installing the MicroPeak software</a></span></dt><dt><span class="section"><a href="#idp53497792">2. Downloading Micro Peak data</a></span></dt><dt><span class="section"><a href="#idp53503952">3. Analyzing MicroPeak Data</a></span></dt><dt><span class="section"><a href="#idp47886320">4. Configuring the MicroPeak application</a></span></dt></dl></div><p>
111 MicroPeak stores barometric pressure information for the first
112 48 seconds of the flight in on-board non-volatile memory. The
113 contents of this memory can be downloaded to a computer using
114 the MicroPeak USB adapter.
115 </p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp53494704"></a>1. Installing the MicroPeak software</h2></div></div></div><p>
116 The MicroPeak application runs on Linux, Mac OS X and
117 Windows. You can download the latest version from
118 <a class="ulink" href="http://altusmetrum.org/AltOS" target="_top">http://altusmetrum.org/AltOS</a>.
120 On Mac OS X and Windows, the FTDI USB device driver needs to
121 be installed. A compatible version of this driver is included
122 with the MicroPeak application, but you may want to download a
123 newer version from <a class="ulink" href="http://www.ftdichip.com/FTDrivers.htm" target="_top">http://www.ftdichip.com/FTDrivers.htm</a>.
124 </p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp53497792"></a>2. Downloading Micro Peak data</h2></div></div></div><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
125 Connect the MicroPeak USB adapter to a USB cable and plug it
127 </p></li><li class="listitem"><p>
128 Start the MicroPeak application, locate the File menu and
129 select the Download entry.
130 </p></li><li class="listitem"><p>
131 The MicroPeak USB adapter has a small phototransistor on
132 the end of the board furthest from the USB
133 connector. Locate this and place the LED on the MicroPeak
134 directly in contact with it. The MicroPeak LED and the
135 MicroPeak USB adapter photo need to be touching—even a
136 millimeters of space between them will reduce the light
137 intensity from the LED enough that the phototransistor
138 will not sense it. Turn on the MicroPeak board and adjust
139 the position until the blue LED on the MicroPeak USB
140 adapter blinks in time with the orange LED on the
142 </p></li><li class="listitem"><p>
143 After the maximum flight height is reported, MicroPeak will
144 pause for a few seconds, blink the LED four times rapidly
145 and then send the data in one long blur on the LED. The
146 MicroPeak application should receive the data. When it does,
147 it will present the data in a graph and offer to save the
148 data to a file. If not, you can power cycle the MicroPeak
150 </p></li></ul></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp53503952"></a>3. Analyzing MicroPeak Data</h2></div></div></div><p>
151 The MicroPeak application can present flight data in the form
152 of a graph, a collection of computed statistics or in tabular
155 MicroPeak collects raw barometric pressure data which is
156 then used to compute the remaining data. Altitude is computed
157 through a standard atmospheric model. Absolute error in this
158 data will be affected by local atmospheric
159 conditions. Fortunately, these errors tend to mostly cancel
160 out, so the error in the height computation is much smaller
161 than the error in altitude would be.
163 Speed and acceleration are computed by first smoothing the
164 height data with a Gaussian window averaging filter. For speed
165 data, this average uses seven samples. For acceleration data,
166 eleven samples are used. These were chosen to provide
167 reasonably smooth speed and acceleration data, which would
168 otherwise be swamped with noise.
170 Under the Graph tab, the height, speed and acceleration values
171 are displayed together. You can zoom in on the graph by
172 clicking and dragging to sweep out an area of
173 interest. Right-click on the plot to bring up a menu that will
174 let you save, copy or print the graph.
176 The Statistics tab presents overall data from the flight. Note
177 that the Maximum height value is taken from the minumum
178 pressure captured in flight, and may be different from the
179 apparant apogee value as the on-board data are sampled twice
180 as fast as the recorded values, or because the true apogee
181 occurred after the on-board memory was full. Each value is
182 presented in several units as appropriate.
184 A table consisting of the both the raw barometric pressure
185 data and values computed from that for each recorded time.
187 The File menu has operations to open existing flight logs,
188 Download new data from MicroPeak, Save a copy of the flight
189 log to a new file, Export the tabular data (as seen in the Raw
190 Data tab) to a file, change the application Preferences, Close
191 the current window or close all windows and Exit the
193 </p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp47886320"></a>4. Configuring the MicroPeak application</h2></div></div></div><p>
194 The MicroPeak application has a few user settings which are
195 configured through the Preferences dialog, which can be
196 accessed from the File menu.
197 </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
198 The Log Directory is where flight data will be saved to
199 and loaded from by default. Of course, you can always
200 navigate to other directories in the file chooser windows,
201 this setting is just the starting point.
202 </p></li><li class="listitem"><p>
203 If you prefer to see your graph data in feet and
204 miles per hour instead of meters and meters per second,
205 you can select Imperial Units.
206 </p></li><li class="listitem"><p>
207 To see what data is actually arriving over the serial
208 port, start the MicroPeak application from a command
209 prompt and select the Serial Debug option. This can be
210 useful in debugging serial communication problems, but
211 most people need never choose this.
212 </p></li><li class="listitem"><p>
213 You can adjust the size of the text in the Statistics tab
214 by changing the Font size preference. There are three
215 settings, with luck one will both fit on your screen and
216 provide readable values.
217 </p></li><li class="listitem"><p>
218 The Look & feel menu shows a list of available
219 application appearance choices. By default, the MicroPeak
220 application tries to blend in with other applications, but
221 you may choose some other appearance if you like.
222 </p></li></ul></div><p>
224 Note that MicroPeak shares a subset of the AltosUI
225 preferences, so if you use both of these applications, change
226 in one application will affect the other.
227 </p></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="idp47894112"></a>Chapter 4. Technical Information</h1></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="section"><a href="#idp47894784">1. Barometric Sensor</a></span></dt><dt><span class="section"><a href="#idp47897392">2. Micro-controller</a></span></dt><dt><span class="section"><a href="#idp47899744">3. Lithium Battery</a></span></dt><dt><span class="section"><a href="#idp47902528">4. Atmospheric Model</a></span></dt><dt><span class="section"><a href="#idp47904928">5. Mechanical Considerations</a></span></dt><dt><span class="section"><a href="#idp47907680">6. On-board data storage</a></span></dt><dt><span class="section"><a href="#idp54636384">7. MicroPeak Programming Interface</a></span></dt></dl></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp47894784"></a>1. Barometric Sensor</h2></div></div></div><p>
228 MicroPeak uses the Measurement Specialties MS5607 sensor. This
229 has a range of 120kPa to 1kPa with an absolute accuracy of
230 150Pa and a resolution of 2.4Pa.
232 The pressure range corresponds roughly to an altitude range of
233 -1500m (-4900 feet) to 31000m (102000 feet), while the
234 resolution is approximately 20cm (8 inches) near sea level and
235 60cm (24in) at 10000m (33000 feet).
237 Ground pressure is computed from an average of 16 samples,
238 taken while the altimeter is at rest. Flight pressure is
239 computed from a Kalman filter designed to smooth out any minor
240 noise in the sensor values.
241 </p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp47897392"></a>2. Micro-controller</h2></div></div></div><p>
242 MicroPeak uses an Atmel ATtiny85 micro-controller. This tiny
243 CPU contains 8kB of flash for the application, 512B of RAM for
244 temporary data storage and 512B of EEPROM for non-volatile
245 storage of previous flight data.
247 The ATtiny85 has a low-power mode which turns off all of the
248 clocks and powers down most of the internal components. In
249 this mode, the chip consumes only .1μA of power. MicroPeak
250 uses this mode once the flight has ended to preserve battery
252 </p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp47899744"></a>3. Lithium Battery</h2></div></div></div><p>
253 The CR1025 battery used by MicroPeak holds 30mAh of power,
254 which is sufficient to run for over 40 hours. Because
255 MicroPeak powers down on landing, run time includes only time
256 sitting on the launch pad or during flight.
258 The large positive terminal (+) is usually marked, while the
259 smaller negative terminal is not. Make sure you install the
260 battery with the positive terminal facing away from the
261 circuit board where it will be in contact with the metal
262 battery holder. A small pad on the circuit board makes contact
263 with the negative battery terminal.
265 Shipping restrictions may prevent us from including a CR1025
266 battery with MicroPeak. If so, many stores carry CR1025
267 batteries as they are commonly used in small electronic
268 devices such as flash lights.
269 </p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp47902528"></a>4. Atmospheric Model</h2></div></div></div><p>
270 MicroPeak contains a fixed atmospheric model which is used to
271 convert barometric pressure into altitude. The model was
272 converted into a 469-element piece wise linear approximation
273 which is then used to compute the altitude of the ground and
274 apogee. The difference between these represents the maximum
275 height of the flight.
277 The model assumes a particular set of atmospheric conditions,
278 which while a reasonable average cannot represent the changing
279 nature of the real atmosphere. Fortunately, for flights
280 reasonably close to the ground, the effect of this global
281 inaccuracy are largely canceled out when the computed ground
282 altitude is subtracted from the computed apogee altitude, so
283 the resulting height is more accurate than either the ground
285 </p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp47904928"></a>5. Mechanical Considerations</h2></div></div></div><p>
286 MicroPeak is designed to be rugged enough for typical rocketry
287 applications. It contains two moving parts, the battery holder
288 and the power switch, which were selected for their
291 The MicroPeak battery holder is designed to withstand impact
292 up to 150g without breaking contact (or, worse yet, causing
293 the battery to fall out). That means it should stand up to
294 almost any launch you care to try, and should withstand fairly
297 The power switch is designed to withstand up to 50g forces in
298 any direction. Because it is a sliding switch, orienting the
299 switch perpendicular to the direction of rocket travel will
300 serve to further protect the switch from launch forces.
301 </p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp47907680"></a>6. On-board data storage</h2></div></div></div><p>
302 The ATtiny85 has 512 bytes of non-volatile storage, separate
303 from the code storage memory. The MicroPeak firmware uses this
304 to store information about the last completed
305 flight. Barometric measurements from the ground before launch
306 and at apogee are stored, and used at power-on to compute the
307 height of the last flight.
309 In addition to the data used to present the height of the last
310 flight, MicroPeak also stores barometric information sampled
311 at regular intervals during the flight. This information can
312 be extracted from MicroPeak through any AVR programming
314 </p><div class="table"><a name="idp47909744"></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>
315 All EEPROM data are stored least-significant byte first. The
316 instantaneous flight pressure data are stored without the
317 upper 16 bits of data. The upper bits can be reconstructed
318 from the previous sample, assuming that pressure doesn't
319 change by more more than 32kPa in a single sample
320 interval. Note that this pressure data is <span class="emphasis"><em>not</em></span>
321 filtered in any way, while both the recorded ground and apogee
322 pressure values are, so you shouldn't expect the minimum
323 instantaneous pressure value to match the recorded minimum
324 pressure value exactly.
326 MicroPeak samples pressure every 96ms, but stores only every
327 other sample in the EEPROM. This provides for 251 pressure
328 samples at 192ms intervals, or 48.192s of storage. The clock
329 used for these samples is a factory calibrated RC circuit
330 built into the ATtiny85 and is accurate only to within ±10% at
331 25°C. So, you can count on the pressure data being accurate,
332 but speed or acceleration data computed from this will be
333 limited by the accuracy of this clock.
334 </p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp54636384"></a>7. MicroPeak Programming Interface</h2></div></div></div><p>
335 MicroPeak exposes a standard 6-pin AVR programming interface,
336 but not using the usual 2x3 array of pins on 0.1"
337 centers. Instead, there is a single row of tiny 0.60mm ×
338 0.85mm pads on 1.20mm centers exposed near the edge of the
339 circuit board. We couldn't find any connector that was
340 small enough to include on the circuit board.
342 In lieu of an actual connector, the easiest way to connect to
343 the bare pads is through a set of Pogo pins. These
344 spring-loaded contacts are designed to connect in precisely
345 this way. We've designed a programming jig, the MicroPeak
346 Pogo Pin board which provides a standard AVR interface on one
347 end and a recessed slot for MicroPeak to align the board with
350 The MicroPeak Pogo Pin board is not a complete AVR programmer,
351 it is an interface board that provides a 3.3V regulated power
352 supply to run the MicroPeak via USB and a standard 6-pin AVR
353 programming interface with the usual 2x3 grid of pins on 0.1"
354 centers. This can be connected to any AVR programming
357 The AVR programming interface cannot run faster than ¼ of the
358 AVR CPU clock frequency. Because MicroPeak runs at 250kHz to
359 save power, you must configure your AVR programming system to
360 clock the AVR programming interface at no faster than
361 62.5kHz, or a clock period of 32µS.
362 </p></div></div></div></body></html>
projects / web / altusmetrum / blob