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="idm14762280"></a>MicroPeak Owner's Manual</h1></div><div><h2 class="subtitle">A peak-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="idp172816"></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></table></div></div></div><hr></div><div class="acknowledgements" title="Acknowledgements"><div class="titlepage"><div><div><h2 class="title"><a name="idp174776"></a>Acknowledgements</h2></div></div></div>
11 Thanks to John Lyngdal for suggesting that we build something like this.
14 Have fun using these products, and we hope to meet all of you
15 out on the rocket flight line somewhere.
16 </p><div class="literallayout"><p><br>
17 Bdale Garbee, KB0G<br>
18 NAR #87103, TRA #12201<br>
20 Keith Packard, KD7SQG<br>
21 NAR #88757, TRA #12200<br>
24 </div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="chapter"><a href="#idp176024">1. Quick Start Guide</a></span></dt><dt><span class="chapter"><a href="#idp1555544">2. Handling Precautions</a></span></dt><dt><span class="chapter"><a href="#idp1561440">3. Technical Information</a></span></dt><dd><dl><dt><span class="section"><a href="#idp3211240">1. Barometric Sensor</a></span></dt><dt><span class="section"><a href="#idp1961960">2. Micro-controller</a></span></dt><dt><span class="section"><a href="#idp2901888">3. Lithium Battery</a></span></dt><dt><span class="section"><a href="#idp1674792">4. Atmospheric Model</a></span></dt><dt><span class="section"><a href="#idp1421872">5. Mechanical Considerations</a></span></dt></dl></dd></dl></div><div class="chapter" title="Chapter 1. Quick Start Guide"><div class="titlepage"><div><div><h2 class="title"><a name="idp176024"></a>Chapter 1. Quick Start Guide</h2></div></div></div><p>
25 MicroPeak is designed to be easy to use. Requiring no external
26 components, flying takes just a few steps
27 </p><div class="itemizedlist"><ul class="itemizedlist" type="disc"><li class="listitem"><p>
28 Install the battery. Fit a CR1025 battery into the plastic
29 carrier. The positive (+) terminal should be towards the more
30 open side of the carrier. Slip the carrier into the battery
31 holder with the positive (+) terminal facing away from the
33 </p></li><li class="listitem"><p>
34 Install MicroPeak in your rocket. This can be as simple as
35 preparing a soft cushion of wadding inside a vented model payload
36 bay. Wherever you mount it, make sure you protect the
37 barometric sensor from corrosive ejection gasses as those
38 will damage the sensor.
39 </p></li><li class="listitem"><p>
40 Turn MicroPeak on. Slide the switch so that the actuator
41 covers the '1' printed on the board. MicroPeak will report
42 the maximum height of the last flight in decimeters using a
43 sequence of flashes on the LED. A sequence of short flashes
44 indicates one digit. A single long flash indicates zero. The
45 height is reported in decimeters, so the last digit will be
46 tenths of a meter. For example, if MicroPeak reports 5 4 4
47 3, then the maximum height of the last flight was 544.3m, or
49 </p></li><li class="listitem"><p>
50 Finish preparing the rocket for flight. After the
51 previous flight data have been reported, MicroPeak waits for
52 30 seconds before starting to check for launch. This gives
53 you time to finish assembling the rocket. As those
54 activities might cause pressure changes inside the airframe,
55 MicroPeak might accidentally detect boost. If you need to do
56 anything to the airframe after the 30 second window passes,
57 make sure to be careful not to disturb the altimeter. The
58 LED will remain dark during the 30 second delay, but after
59 that, it will start blinking once every 3 seconds.
60 </p></li><li class="listitem"><p>
61 Fly the rocket. Once the rocket passes about 10m in height
62 (32 feet), the micro-controller will record the ground
63 pressure and track the pressure seen during the flight. In
64 this mode, the LED flickers rapidly. When the rocket lands,
65 and the pressure stabilizes, the micro-controller will record
66 the minimum pressure pressure experienced during the flight,
67 compute the height represented by the difference in air
68 pressure and blink that value out on the LED. After that,
69 MicroPeak powers down to conserve battery power.
70 </p></li><li class="listitem"><p>
71 Recover the data. Turn MicroPeak off for a couple of seconds
72 (to discharge the capacitors) and then back on. MicroPeak
73 will blink out the maximum height for the last flight. Turn
74 MicroPeak back off to conserve battery power.
75 </p></li></ul></div></div><div class="chapter" title="Chapter 2. Handling Precautions"><div class="titlepage"><div><div><h2 class="title"><a name="idp1555544"></a>Chapter 2. Handling Precautions</h2></div></div></div><p>
76 All Altus Metrum products are sophisticated electronic devices.
77 When handled gently and properly installed in an air-frame, they
78 will deliver impressive results. However, as with all electronic
79 devices, there are some precautions you must take.
81 The CR1025 Lithium batteries have an
82 extraordinary power density. This is great because we can fly with
83 much less battery mass... but if they are punctured
84 or their contacts are allowed to short, they can and will release their
86 Thus we recommend that you take some care when handling MicroPeak
87 to keep conductive material from coming in contact with the exposed metal elements.
89 The barometric sensors used in MicroPeak is
90 sensitive to sunlight. Please consider this when
91 designing an installation, for example, in an air-frame with a
92 see-through plastic payload bay. Many model rockets with payload bays
93 use clear plastic for the payload bay. Replacing these with an opaque
94 cardboard tube, painting them, or wrapping them with a layer of masking
95 tape are all reasonable approaches to keep the sensor out of direct
98 The barometric sensor sampling ports must be able to "breathe",
99 both by not being covered by foam or tape or other materials that might
100 directly block the hole on the top of the sensor, and also by having a
101 suitable static vent to outside air.
103 As with all other rocketry electronics, Altus Metrum altimeters must
104 be protected from exposure to corrosive motor exhaust and ejection
106 </p></div><div class="chapter" title="Chapter 3. Technical Information"><div class="titlepage"><div><div><h2 class="title"><a name="idp1561440"></a>Chapter 3. Technical Information</h2></div></div></div><div class="toc"><p><b>Table of Contents</b></p><dl><dt><span class="section"><a href="#idp3211240">1. Barometric Sensor</a></span></dt><dt><span class="section"><a href="#idp1961960">2. Micro-controller</a></span></dt><dt><span class="section"><a href="#idp2901888">3. Lithium Battery</a></span></dt><dt><span class="section"><a href="#idp1674792">4. Atmospheric Model</a></span></dt><dt><span class="section"><a href="#idp1421872">5. Mechanical Considerations</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="idp3211240"></a>1. Barometric Sensor</h2></div></div></div><p>
107 MicroPeak uses the Measurement Specialties MS5607 sensor. This
108 has a range of 120kPa to 1kPa with an absolute accuracy of
109 150Pa and a resolution of 2.4Pa.
111 The pressure range corresponds roughly to an altitude range of
112 -1500m (-4900 feet) to 31000m (102000 feet), while the
113 resolution is approximately 20cm (8 inches) near sea level and
114 60cm (24in) at 10000m (33000 feet).
116 Ground pressure is computed from an average of 16 samples,
117 taken while the altimeter is at rest. Flight pressure is
118 computed from an exponential IIR filter designed to smooth out
119 transients caused by mechanical stress on the barometer.
120 </p></div><div class="section" title="2. Micro-controller"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp1961960"></a>2. Micro-controller</h2></div></div></div><p>
121 MicroPeak uses an Atmel ATtiny85 micro-controller. This tiny
122 CPU contains 8kB of flash for the application, 512B of RAM for
123 temporary data storage and 512B of EEPROM for non-volatile
124 storage of previous flight data.
126 The ATtiny85 has a low-power mode which turns off all of the
127 clocks and powers down most of the internal components. In
128 this mode, the chip consumes only .1μA of power. MicroPeak
129 uses this mode once the flight has ended to preserve battery
131 </p></div><div class="section" title="3. Lithium Battery"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp2901888"></a>3. Lithium Battery</h2></div></div></div><p>
132 The CR1025 battery used by MicroPeak holes 30mAh of power,
133 which is sufficient to run for over 15 hours. Because
134 MicroPeak powers down on landing, run time includes only time
135 sitting on the launch pad or during flight.
137 The large positive terminal (+) is usually marked, while the
138 smaller negative terminal is not. Make sure you install the
139 battery with the positive terminal facing away from the
140 circuit board where it will be in contact with the metal
141 battery holder. A small pad on the circuit board makes contact
142 with the negative battery terminal.
144 Shipping restrictions prevent us from including a CR1025
145 battery with MicroPeak. Many stores carry CR1025 batteries as
146 they are commonly used in small electronic devices such as
148 </p></div><div class="section" title="4. Atmospheric Model"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp1674792"></a>4. Atmospheric Model</h2></div></div></div><p>
149 MicroPeak contains a fixed atmospheric model which is used to
150 convert barometric pressure into altitude. The model was
151 converted into a 469-element piece wise linear approximation
152 which is then used to compute the altitude of the ground and
153 apogee. The difference between these represents the maximum
154 height of the flight.
156 The model assumes a particular set of atmospheric conditions,
157 which while a reasonable average cannot represent the changing
158 nature of the real atmosphere. Fortunately, for flights
159 reasonably close to the ground, the effect of this global
160 inaccuracy are largely canceled out when the computed ground
161 altitude is subtracted from the computed apogee altitude, so
162 the resulting height is more accurate than either the ground
164 </p></div><div class="section" title="5. Mechanical Considerations"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="idp1421872"></a>5. Mechanical Considerations</h2></div></div></div><p>
165 MicroPeak is designed to be rugged enough for typical rocketry
166 applications. It contains two moving parts, the battery holder
167 and the power switch, which were selected for their
170 The MicroPeak battery holder is designed to withstand impact
171 up to 150g without breaking contact (or, worse yet, causing
172 the battery to fall out). That means it should stand up to
173 almost any launch you care to try, and should withstand fairly
176 The power switch is designed to withstand up to 50g forces in
177 any direction. Because it is a sliding switch, orienting the
178 switch perpendicular to the direction of rocket travel will
179 serve to further protect the switch from launch forces.
180 </p></div></div></div></body></html>
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