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="idm6233120"></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 © 2014 Bdale Garbee and Keith Packard</p></div><div><div class="legalnotice"><a name="idp47879728"></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><tr><td align="left">Revision 1.3.2</td><td align="left">12 February 2014</td></tr><tr><td align="left" colspan="2">
18 Add a "Download" button to the main window, which makes it
19 quicker to access the download function. Update the data
20 download documentation to reflect the new MicroPeak USB
21 adapter design. Monitor data during download to let you see
22 if the USB connection is working at all by showing the
23 characters received from the MicroPeak USB adapter.
24 </td></tr></table></div></div></div><hr></div><div class="dedication"><div class="titlepage"><div><div><h1 class="title"><a name="idp48909504"></a>Acknowledgements</h1></div></div></div><p>
25 Thanks to John Lyngdal for suggesting that we build something like this.
27 Have fun using these products, and we hope to meet all of you
28 out on the rocket flight line somewhere.
29 </p><div class="literallayout"><p><br>
30 Bdale Garbee, KB0G<br>
31 NAR #87103, TRA #12201<br>
33 Keith Packard, KD7SQG<br>
34 NAR #88757, TRA #12200<br>
36 </p></div><div class="toc"><p><b>Table of Contents</b></p><dl class="toc"><dt><span class="chapter"><a href="#idp48912256">1. Quick Start Guide</a></span></dt><dt><span class="chapter"><a href="#idp47997744">2. Handling Precautions</a></span></dt><dt><span class="chapter"><a href="#idp48002128">3. The MicroPeak USB adapter</a></span></dt><dd><dl><dt><span class="section"><a href="#idp48005680">1. Installing the MicroPeak software</a></span></dt><dt><span class="section"><a href="#idp48008768">2. Downloading Micro Peak data</a></span></dt><dt><span class="section"><a href="#idp47907248">3. Analyzing MicroPeak Data</a></span></dt><dd><dl><dt><span class="section"><a href="#idp47910736">3.1. MicroPeak Graphs</a></span></dt><dt><span class="section"><a href="#idp47914336">3.2. MicroPeak Flight Statistics</a></span></dt><dt><span class="section"><a href="#idp47918208">3.3. Raw Data</a></span></dt><dt><span class="section"><a href="#idp53789120">3.4. Configuring the Graph</a></span></dt></dl></dd><dt><span class="section"><a href="#idp53792736">4. Setting MicroPeak Preferences</a></span></dt></dl></dd><dt><span class="chapter"><a href="#idp53802768">4. Technical Information</a></span></dt><dd><dl><dt><span class="section"><a href="#idp53803440">1. Barometric Sensor</a></span></dt><dt><span class="section"><a href="#idp53806192">2. Micro-controller</a></span></dt><dt><span class="section"><a href="#idp53808544">3. Lithium Battery</a></span></dt><dt><span class="section"><a href="#idp53811328">4. Atmospheric Model</a></span></dt><dt><span class="section"><a href="#idp53814304">5. Mechanical Considerations</a></span></dt><dt><span class="section"><a href="#idp53817056">6. On-board data storage</a></span></dt><dt><span class="section"><a href="#idp53837344">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="#idp53819168">MicroPeak EEPROM Data Storage</a></dt></dl></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="idp48912256"></a>Chapter 1. Quick Start Guide</h1></div></div></div><p>
37 MicroPeak is designed to be easy to use. Requiring no external
38 components, flying takes just a few steps
39 </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
40 Install the battery. Fit a CR1025 battery into the plastic
41 carrier. The positive (+) terminal should be towards the more
42 open side of the carrier. Slip the carrier into the battery
43 holder with the positive (+) terminal facing away from the
45 </p><div class="informalfigure"><div class="mediaobject"><table border="0" summary="manufactured viewport for HTML img" style="cellpadding: 0; cellspacing: 0;" width="405"><tr><td><img src="micropeak-back.jpg" width="405"></td></tr></table></div></div></li><li class="listitem"><p>
46 Install MicroPeak in your rocket. This can be as simple as
47 preparing a soft cushion of wadding inside a vented model payload
48 bay. Wherever you mount it, make sure you protect the
49 barometric sensor from corrosive ejection gasses as those
50 will damage the sensor, and shield it from light as that can
51 cause incorrect sensor readings.
52 </p></li><li class="listitem"><p>
53 Turn MicroPeak on. Slide the switch so that the actuator
54 covers the '1' printed on the board. MicroPeak will report
55 the maximum height of the last flight in decimeters using a
56 sequence of flashes on the LED. A sequence of short flashes
57 indicates one digit. A single long flash indicates zero. The
58 height is reported in decimeters, so the last digit will be
59 tenths of a meter. For example, if MicroPeak reports 5 4 4
60 3, then the maximum height of the last flight was 544.3m, or
62 </p></li><li class="listitem"><p>
63 Finish preparing the rocket for flight. After the
64 previous flight data have been reported, MicroPeak waits for
65 one minute before starting to check for launch. This gives
66 you time to finish assembling the rocket. As those
67 activities might cause pressure changes inside the airframe,
68 MicroPeak might accidentally detect boost. If you need to do
69 anything to the airframe after the one minute window passes,
70 make sure to be careful not to disturb the altimeter. The
71 LED will remain dark during the one minute delay, but after
72 that, it will start blinking once every 3 seconds.
73 </p></li><li class="listitem"><p>
74 Fly the rocket. Once the rocket passes about 30m in height
75 (100 feet), the micro-controller will record the ground
76 pressure and track the pressure seen during the flight. In
77 this mode, the LED flickers rapidly. When the rocket lands,
78 and the pressure stabilizes, the micro-controller will record
79 the minimum pressure pressure experienced during the flight,
80 compute the height represented by the difference in air
81 pressure and blink that value out on the LED. After that,
82 MicroPeak powers down to conserve battery power.
83 </p></li><li class="listitem"><p>
84 Recover the data. Turn MicroPeak off and then back on. MicroPeak
85 will blink out the maximum height for the last flight. Turn
86 MicroPeak back off to conserve battery power.
87 </p></li></ul></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="idp47997744"></a>Chapter 2. Handling Precautions</h1></div></div></div><p>
88 All Altus Metrum products are sophisticated electronic devices.
89 When handled gently and properly installed in an air-frame, they
90 will deliver impressive results. However, as with all electronic
91 devices, there are some precautions you must take.
93 The CR1025 Lithium batteries have an
94 extraordinary power density. This is great because we can fly with
95 much less battery mass... but if they are punctured
96 or their contacts are allowed to short, they can and will release their
98 Thus we recommend that you take some care when handling MicroPeak
99 to keep conductive material from coming in contact with the exposed metal elements.
101 The barometric sensor used in MicroPeak is sensitive to
102 sunlight. Please consider this when designing an
103 installation. Many model rockets with payload bays use clear
104 plastic for the payload bay. Replacing these with an opaque
105 cardboard tube, painting them, or wrapping them with a layer of
106 masking tape are all reasonable approaches to keep the sensor
107 out of direct sunlight.
109 The barometric sensor sampling ports must be able to "breathe",
110 both by not being covered by foam or tape or other materials that might
111 directly block the hole on the top of the sensor, and also by having a
112 suitable static vent to outside air.
114 As with all other rocketry electronics, Altus Metrum altimeters must
115 be protected from exposure to corrosive motor exhaust and ejection
117 </p></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="idp48002128"></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="#idp48005680">1. Installing the MicroPeak software</a></span></dt><dt><span class="section"><a href="#idp48008768">2. Downloading Micro Peak data</a></span></dt><dt><span class="section"><a href="#idp47907248">3. Analyzing MicroPeak Data</a></span></dt><dd><dl><dt><span class="section"><a href="#idp47910736">3.1. MicroPeak Graphs</a></span></dt><dt><span class="section"><a href="#idp47914336">3.2. MicroPeak Flight Statistics</a></span></dt><dt><span class="section"><a href="#idp47918208">3.3. Raw Data</a></span></dt><dt><span class="section"><a href="#idp53789120">3.4. Configuring the Graph</a></span></dt></dl></dd><dt><span class="section"><a href="#idp53792736">4. Setting MicroPeak Preferences</a></span></dt></dl></div><div class="informalfigure"><div class="mediaobject"><table border="0" summary="manufactured viewport for HTML img" style="cellpadding: 0; cellspacing: 0;" width="405"><tr><td><img src="MicroPeakUSB-2.0.jpg" width="405"></td></tr></table></div></div><p>
118 MicroPeak stores barometric pressure information for the first
119 48 seconds of the flight in on-board non-volatile memory. The
120 contents of this memory can be downloaded to a computer using
121 the MicroPeak USB adapter.
122 </p><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp48005680"></a>1. Installing the MicroPeak software</h2></div></div></div><p>
123 The MicroPeak application runs on Linux, Mac OS X and
124 Windows. You can download the latest version from
125 <a class="ulink" href="http://altusmetrum.org/AltOS" target="_top">http://altusmetrum.org/AltOS</a>.
127 On Mac OS X and Windows, the FTDI USB device driver needs to
128 be installed. A compatible version of this driver is included
129 with the MicroPeak application, but you may want to download a
130 newer version from <a class="ulink" href="http://www.ftdichip.com/FTDrivers.htm" target="_top">http://www.ftdichip.com/FTDrivers.htm</a>.
131 </p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp48008768"></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>
132 Plug the MicroPeak USB adapter in to your computer.
133 </p></li><li class="listitem"><p>
134 Start the MicroPeak application.
135 </p><div class="informalfigure"><div class="mediaobject"><table border="0" summary="manufactured viewport for HTML img" style="cellpadding: 0; cellspacing: 0;" width="45"><tr><td><img src="micropeak-nofont.svg" width="45"></td></tr></table></div></div></li><li class="listitem"><p>
136 Click on the Download button at the top of the window.
137 </p><div class="informalfigure"><div class="mediaobject"><table border="0" summary="manufactured viewport for HTML img" style="cellpadding: 0; cellspacing: 0;" width="405"><tr><td><img src="micropeak-app.png" width="405"></td></tr></table></div></div></li><li class="listitem"><p>
138 Select from the listed devices. There will probably be
140 </p><div class="informalfigure"><div class="mediaobject"><table border="0" summary="manufactured viewport for HTML img" style="cellpadding: 0; cellspacing: 0;" width="207"><tr><td><img src="micropeak-device-dialog.png" width="207"></td></tr></table></div></div></li><li class="listitem"><p>
141 The application will now wait until it receives valid data
142 from the MicroPeak USB adapter.
143 </p><div class="informalfigure"><div class="mediaobject"><table border="0" summary="manufactured viewport for HTML img" style="cellpadding: 0; cellspacing: 0;" width="180"><tr><td><img src="micropeak-download.png" width="180"></td></tr></table></div></div><p>
144 The MicroPeak USB adapter has a small phototransistor
145 under the hole in the center of the box.
146 Locate this, turn on the MicroPeak and place the orange LED on the MicroPeak
147 directly inside the hole, resting the MicroPeak itself on
148 the box. You should see the blue LED on the MicroPeak USB
149 adapter blinking in time with the orange LED on the
150 MicroPeak board itself.
151 </p><div class="informalfigure"><div class="mediaobject"><table border="0" summary="manufactured viewport for HTML img" style="cellpadding: 0; cellspacing: 0;" width="405"><tr><td><img src="MicroPeakUSB-2.0-inuse.jpg" width="405"></td></tr></table></div></div></li><li class="listitem"><p>
152 After the maximum flight height is reported, MicroPeak will
153 pause for a few seconds, blink the LED four times rapidly
154 and then send the data in one long blur on the LED. The
155 MicroPeak application should receive the data. When it does,
156 it will present the data in a graph and offer to save the
157 data to a file. If not, you can power cycle the MicroPeak
159 </p><div class="informalfigure"><div class="mediaobject"><table border="0" summary="manufactured viewport for HTML img" style="cellpadding: 0; cellspacing: 0;" width="207"><tr><td><img src="micropeak-save-dialog.png" width="207"></td></tr></table></div></div></li><li class="listitem"><p>
160 Once the data are saved, a graph will be displayed with
161 height, speed and acceleration values computed from the
162 recorded barometric pressure data. See the next section
163 for more details on that.
164 </p></li></ul></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp47907248"></a>3. Analyzing MicroPeak Data</h2></div></div></div><p>
165 The MicroPeak application can present flight data in the form
166 of a graph, a collection of computed statistics or in tabular
169 MicroPeak collects raw barometric pressure data which is
170 then used to compute the remaining data. Altitude is computed
171 through a standard atmospheric model. Absolute error in this
172 data will be affected by local atmospheric
173 conditions. Fortunately, these errors tend to mostly cancel
174 out, so the error in the height computation is much smaller
175 than the error in altitude would be.
177 Speed and acceleration are computed by first smoothing the
178 height data with a Gaussian window averaging filter. For speed
179 data, this average uses seven samples. For acceleration data,
180 eleven samples are used. These were chosen to provide
181 reasonably smooth speed and acceleration data, which would
182 otherwise be swamped with noise.
184 The File menu has operations to open existing flight logs,
185 Download new data from MicroPeak, Save a copy of the flight
186 log to a new file, Export the tabular data (as seen in the Raw
187 Data tab) to a file, change the application Preferences, Close
188 the current window or close all windows and Exit the
190 </p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp47910736"></a>3.1. MicroPeak Graphs</h3></div></div></div><p>
191 Under the Graph tab, the height, speed and acceleration values
192 are displayed together. You can zoom in on the graph by
193 clicking and dragging to sweep out an area of
194 interest. Right-click on the plot to bring up a menu that will
195 let you save, copy or print the graph.
196 </p><div class="informalfigure"><div class="mediaobject"><table border="0" summary="manufactured viewport for HTML img" style="cellpadding: 0; cellspacing: 0;" width="405"><tr><td><img src="micropeak-graph.png" width="405"></td></tr></table></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp47914336"></a>3.2. MicroPeak Flight Statistics</h3></div></div></div><p>
197 The Statistics tab presents overall data from the flight. Note
198 that the Maximum height value is taken from the minumum
199 pressure captured in flight, and may be different from the
200 apparant apogee value as the on-board data are sampled twice
201 as fast as the recorded values, or because the true apogee
202 occurred after the on-board memory was full. Each value is
203 presented in several units as appropriate.
204 </p><div class="informalfigure"><div class="mediaobject"><table border="0" summary="manufactured viewport for HTML img" style="cellpadding: 0; cellspacing: 0;" width="405"><tr><td><img src="micropeak-statistics.png" width="405"></td></tr></table></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp47918208"></a>3.3. Raw Data</h3></div></div></div><p>
205 A table consisting of the both the raw barometric pressure
206 data and values computed from that for each recorded time.
207 </p><div class="informalfigure"><div class="mediaobject"><table border="0" summary="manufactured viewport for HTML img" style="cellpadding: 0; cellspacing: 0;" width="405"><tr><td><img src="micropeak-raw-data.png" width="405"></td></tr></table></div></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="idp53789120"></a>3.4. Configuring the Graph</h3></div></div></div><p>
208 This selects which graph elements to show, and lets you
209 switch between metric and imperial units
210 </p><div class="informalfigure"><div class="mediaobject"><table border="0" summary="manufactured viewport for HTML img" style="cellpadding: 0; cellspacing: 0;" width="405"><tr><td><img src="micropeak-graph-configure.png" width="405"></td></tr></table></div></div></div></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp53792736"></a>4. Setting MicroPeak Preferences</h2></div></div></div><div class="informalfigure"><div class="mediaobject"><table border="0" summary="manufactured viewport for HTML img" style="cellpadding: 0; cellspacing: 0;" width="162"><tr><td><img src="micropeak-preferences.png" width="162"></td></tr></table></div></div><p>
211 The MicroPeak application has a few user settings which are
212 configured through the Preferences dialog, which can be
213 accessed from the File menu.
214 </p><div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem"><p>
215 The Log Directory is where flight data will be saved to
216 and loaded from by default. Of course, you can always
217 navigate to other directories in the file chooser windows,
218 this setting is just the starting point.
219 </p></li><li class="listitem"><p>
220 If you prefer to see your graph data in feet and
221 miles per hour instead of meters and meters per second,
222 you can select Imperial Units.
223 </p></li><li class="listitem"><p>
224 To see what data is actually arriving over the serial
225 port, start the MicroPeak application from a command
226 prompt and select the Serial Debug option. This can be
227 useful in debugging serial communication problems, but
228 most people need never choose this.
229 </p></li><li class="listitem"><p>
230 You can adjust the size of the text in the Statistics tab
231 by changing the Font size preference. There are three
232 settings, with luck one will both fit on your screen and
233 provide readable values.
234 </p></li><li class="listitem"><p>
235 The Look & feel menu shows a list of available
236 application appearance choices. By default, the MicroPeak
237 application tries to blend in with other applications, but
238 you may choose some other appearance if you like.
239 </p></li></ul></div><p>
241 Note that MicroPeak shares a subset of the AltosUI
242 preferences, so if you use both of these applications, change
243 in one application will affect the other.
244 </p></div></div><div class="chapter"><div class="titlepage"><div><div><h1 class="title"><a name="idp53802768"></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="#idp53803440">1. Barometric Sensor</a></span></dt><dt><span class="section"><a href="#idp53806192">2. Micro-controller</a></span></dt><dt><span class="section"><a href="#idp53808544">3. Lithium Battery</a></span></dt><dt><span class="section"><a href="#idp53811328">4. Atmospheric Model</a></span></dt><dt><span class="section"><a href="#idp53814304">5. Mechanical Considerations</a></span></dt><dt><span class="section"><a href="#idp53817056">6. On-board data storage</a></span></dt><dt><span class="section"><a href="#idp53837344">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="idp53803440"></a>1. Barometric Sensor</h2></div></div></div><p>
245 MicroPeak uses the Measurement Specialties MS5607 sensor. This
246 has a range of 120kPa to 1kPa with an absolute accuracy of
247 150Pa and a resolution of 2.4Pa.
249 The pressure range corresponds roughly to an altitude range of
250 -1500m (-4900 feet) to 31000m (102000 feet), while the
251 resolution is approximately 20cm (8 inches) near sea level and
252 60cm (24in) at 10000m (33000 feet).
254 Ground pressure is computed from an average of 16 samples,
255 taken while the altimeter is at rest. The flight pressure used to
256 report maximum height is computed from a Kalman filter
257 designed to smooth out any minor noise in the sensor
258 values. The flight pressure recorded to non-volatile storage
259 is unfiltered, coming directly from the pressure sensor.
260 </p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp53806192"></a>2. Micro-controller</h2></div></div></div><p>
261 MicroPeak uses an Atmel ATtiny85 micro-controller. This tiny
262 CPU contains 8kB of flash for the application, 512B of RAM for
263 temporary data storage and 512B of EEPROM for non-volatile
264 storage of previous flight data.
266 The ATtiny85 has a low-power mode which turns off all of the
267 clocks and powers down most of the internal components. In
268 this mode, the chip consumes only .1μA of power. MicroPeak
269 uses this mode once the flight has ended to preserve battery
271 </p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp53808544"></a>3. Lithium Battery</h2></div></div></div><p>
272 The CR1025 battery used by MicroPeak holds 30mAh of power,
273 which is sufficient to run for over 40 hours. Because
274 MicroPeak powers down on landing, run time includes only time
275 sitting on the launch pad or during flight.
277 The large positive terminal (+) is usually marked, while the
278 smaller negative terminal is not. Make sure you install the
279 battery with the positive terminal facing away from the
280 circuit board where it will be in contact with the metal
281 battery holder. A small pad on the circuit board makes contact
282 with the negative battery terminal.
284 Shipping restrictions may prevent us from including a CR1025
285 battery with MicroPeak. If so, many stores carry CR1025
286 batteries as they are commonly used in small electronic
287 devices such as flash lights.
288 </p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp53811328"></a>4. Atmospheric Model</h2></div></div></div><p>
289 MicroPeak contains a fixed atmospheric model which is used to
290 convert barometric pressure into altitude. The model was
291 converted into a 469-element piece-wise linear approximation
292 which is then used to compute the altitude of the ground and
293 apogee. The difference between these represents the maximum
294 height of the flight.
296 The model assumes a particular set of atmospheric conditions,
297 which, while a reasonable average, cannot represent the changing
298 nature of the real atmosphere. Fortunately, for flights
299 reasonably close to the ground, the effect of this global
300 inaccuracy are largely canceled out when the computed ground
301 altitude is subtracted from the computed apogee altitude, so
302 the resulting height is more accurate than either the ground
305 Because the raw pressure data is recorded to non-volatile
306 storage, you can use that, along with a more sophisticated
307 atmospheric model, to compute your own altitude values.
308 </p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp53814304"></a>5. Mechanical Considerations</h2></div></div></div><p>
309 MicroPeak is designed to be rugged enough for typical rocketry
310 applications. It contains two moving parts, the battery holder
311 and the power switch, which were selected for their
314 The MicroPeak battery holder is designed to withstand impact
315 up to 150g without breaking contact (or, worse yet, causing
316 the battery to fall out). That means it should stand up to
317 almost any launch you care to try, and should withstand fairly
320 The power switch is designed to withstand up to 50g forces in
321 any direction. Because it is a sliding switch, orienting the
322 switch perpendicular to the direction of rocket travel will
323 serve to further protect the switch from launch forces.
324 </p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp53817056"></a>6. On-board data storage</h2></div></div></div><p>
325 The ATtiny85 has 512 bytes of non-volatile storage, separate
326 from the code storage memory. The MicroPeak firmware uses this
327 to store information about the last completed
328 flight. Barometric measurements from the ground before launch
329 and at apogee are stored, and used at power-on to compute the
330 height of the last flight.
332 In addition to the data used to present the height of the last
333 flight, MicroPeak also stores barometric information sampled
334 at regular intervals during the flight. This is the
335 information captured with the MicroPeak USB adapter. It can
336 also be read from MicroPeak through any AVR programming
338 </p><div class="table"><a name="idp53819168"></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>
339 All EEPROM data are stored least-significant byte first. The
340 instantaneous flight pressure data are stored without the
341 upper 16 bits of data. The upper bits can be reconstructed
342 from the previous sample, assuming that pressure doesn't
343 change by more more than 32kPa in a single sample
344 interval. Note that this pressure data is <span class="emphasis"><em>not</em></span>
345 filtered in any way, while both the recorded ground and apogee
346 pressure values are, so you shouldn't expect the minimum
347 instantaneous pressure value to match the recorded minimum
348 pressure value exactly.
350 MicroPeak samples pressure every 96ms, but stores only every
351 other sample in the EEPROM. This provides for 251 pressure
352 samples at 192ms intervals, or 48.192s of storage. The clock
353 used for these samples is a factory calibrated RC circuit
354 built into the ATtiny85 and is accurate only to within ±10% at
355 25°C. So, you can count on the pressure data being accurate,
356 but speed or acceleration data computed from this will be
357 limited by the accuracy of this clock.
358 </p></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp53837344"></a>7. MicroPeak Programming Interface</h2></div></div></div><p>
359 MicroPeak exposes a standard 6-pin AVR programming interface,
360 but not using the usual 2x3 array of pins on 0.1"
361 centers. Instead, there is a single row of tiny 0.60mm ×
362 0.85mm pads on 1.20mm centers exposed near the edge of the
363 circuit board. We couldn't find any connector that was
364 small enough to include on the circuit board.
366 In lieu of an actual connector, the easiest way to connect to
367 the bare pads is through a set of Pogo pins. These
368 spring-loaded contacts are designed to connect in precisely
369 this way. We've designed a programming jig, the MicroPeak
370 Pogo Pin board which provides a standard AVR interface on one
371 end and a recessed slot for MicroPeak to align the board with
374 The MicroPeak Pogo Pin board is not a complete AVR programmer,
375 it is an interface board that provides a 3.3V regulated power
376 supply to run the MicroPeak via USB and a standard 6-pin AVR
377 programming interface with the usual 2x3 grid of pins on 0.1"
378 centers. This can be connected to any AVR programming
381 The AVR programming interface cannot run faster than ¼ of the
382 AVR CPU clock frequency. Because MicroPeak runs at 250kHz to
383 save power, you must configure your AVR programming system to
384 clock the AVR programming interface at no faster than
385 62.5kHz, or a clock period of 32µS.
386 </p></div></div></div></body></html>
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