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5 <title>MicroPeak Owner's Manual</title>
6 <subtitle>A peak-recording altimeter for hobby rocketry</subtitle>
9 <firstname>Keith</firstname>
10 <surname>Packard</surname>
14 <holder>Bdale Garbee and Keith Packard</holder>
18 This document is released under the terms of the
19 <ulink url="http://creativecommons.org/licenses/by-sa/3.0/">
20 Creative Commons ShareAlike 3.0
27 <revnumber>0.1</revnumber>
28 <date>29 October 2012</date>
30 Initial release with preliminary hardware.
34 <revnumber>1.0</revnumber>
35 <date>18 November 2012</date>
37 Updates for version 1.0 release.
44 Thanks to John Lyngdal for suggesting that we build something like this.
47 Have fun using these products, and we hope to meet all of you
48 out on the rocket flight line somewhere.
51 NAR #87103, TRA #12201
54 NAR #88757, TRA #12200
59 <title>Quick Start Guide</title>
61 MicroPeak is designed to be easy to use. Requiring no external
62 components, flying takes just a few steps
67 Install the battery. Fit a CR1025 battery into the plastic
68 carrier. The positive (+) terminal should be towards the more
69 open side of the carrier. Slip the carrier into the battery
70 holder with the positive (+) terminal facing away from the
76 Install MicroPeak in your rocket. This can be as simple as
77 preparing a soft cushion of wadding inside a vented model payload
78 bay. Wherever you mount it, make sure you protect the
79 barometric sensor from corrosive ejection gasses as those
80 will damage the sensor, and shield it from light as that can
81 cause incorrect sensor readings.
86 Turn MicroPeak on. Slide the switch so that the actuator
87 covers the '1' printed on the board. MicroPeak will report
88 the maximum height of the last flight in decimeters using a
89 sequence of flashes on the LED. A sequence of short flashes
90 indicates one digit. A single long flash indicates zero. The
91 height is reported in decimeters, so the last digit will be
92 tenths of a meter. For example, if MicroPeak reports 5 4 4
93 3, then the maximum height of the last flight was 544.3m, or
99 Finish preparing the rocket for flight. After the
100 previous flight data have been reported, MicroPeak waits for
101 30 seconds before starting to check for launch. This gives
102 you time to finish assembling the rocket. As those
103 activities might cause pressure changes inside the airframe,
104 MicroPeak might accidentally detect boost. If you need to do
105 anything to the airframe after the 30 second window passes,
106 make sure to be careful not to disturb the altimeter. The
107 LED will remain dark during the 30 second delay, but after
108 that, it will start blinking once every 3 seconds.
113 Fly the rocket. Once the rocket passes about 10m in height
114 (32 feet), the micro-controller will record the ground
115 pressure and track the pressure seen during the flight. In
116 this mode, the LED flickers rapidly. When the rocket lands,
117 and the pressure stabilizes, the micro-controller will record
118 the minimum pressure pressure experienced during the flight,
119 compute the height represented by the difference in air
120 pressure and blink that value out on the LED. After that,
121 MicroPeak powers down to conserve battery power.
126 Recover the data. Turn MicroPeak off and then back on. MicroPeak
127 will blink out the maximum height for the last flight. Turn
128 MicroPeak back off to conserve battery power.
134 <title>Handling Precautions</title>
136 All Altus Metrum products are sophisticated electronic devices.
137 When handled gently and properly installed in an air-frame, they
138 will deliver impressive results. However, as with all electronic
139 devices, there are some precautions you must take.
142 The CR1025 Lithium batteries have an
143 extraordinary power density. This is great because we can fly with
144 much less battery mass... but if they are punctured
145 or their contacts are allowed to short, they can and will release their
147 Thus we recommend that you take some care when handling MicroPeak
148 to keep conductive material from coming in contact with the exposed metal elements.
151 The barometric sensor used in MicroPeak is sensitive to
152 sunlight. Please consider this when designing an
153 installation. Many model rockets with payload bays use clear
154 plastic for the payload bay. Replacing these with an opaque
155 cardboard tube, painting them, or wrapping them with a layer of
156 masking tape are all reasonable approaches to keep the sensor
157 out of direct sunlight.
160 The barometric sensor sampling ports must be able to "breathe",
161 both by not being covered by foam or tape or other materials that might
162 directly block the hole on the top of the sensor, and also by having a
163 suitable static vent to outside air.
166 As with all other rocketry electronics, Altus Metrum altimeters must
167 be protected from exposure to corrosive motor exhaust and ejection
172 <title>Technical Information</title>
174 <title>Barometric Sensor</title>
176 MicroPeak uses the Measurement Specialties MS5607 sensor. This
177 has a range of 120kPa to 1kPa with an absolute accuracy of
178 150Pa and a resolution of 2.4Pa.
181 The pressure range corresponds roughly to an altitude range of
182 -1500m (-4900 feet) to 31000m (102000 feet), while the
183 resolution is approximately 20cm (8 inches) near sea level and
184 60cm (24in) at 10000m (33000 feet).
187 Ground pressure is computed from an average of 16 samples,
188 taken while the altimeter is at rest. Flight pressure is
189 computed from an exponential IIR filter designed to smooth out
190 transients caused by mechanical stress on the barometer.
194 <title>Micro-controller</title>
196 MicroPeak uses an Atmel ATtiny85 micro-controller. This tiny
197 CPU contains 8kB of flash for the application, 512B of RAM for
198 temporary data storage and 512B of EEPROM for non-volatile
199 storage of previous flight data.
202 The ATtiny85 has a low-power mode which turns off all of the
203 clocks and powers down most of the internal components. In
204 this mode, the chip consumes only .1μA of power. MicroPeak
205 uses this mode once the flight has ended to preserve battery
210 <title>Lithium Battery</title>
212 The CR1025 battery used by MicroPeak holes 30mAh of power,
213 which is sufficient to run for over 40 hours. Because
214 MicroPeak powers down on landing, run time includes only time
215 sitting on the launch pad or during flight.
218 The large positive terminal (+) is usually marked, while the
219 smaller negative terminal is not. Make sure you install the
220 battery with the positive terminal facing away from the
221 circuit board where it will be in contact with the metal
222 battery holder. A small pad on the circuit board makes contact
223 with the negative battery terminal.
226 Shipping restrictions prevent us from including a CR1025
227 battery with MicroPeak. Many stores carry CR1025 batteries as
228 they are commonly used in small electronic devices such as
233 <title>Atmospheric Model</title>
235 MicroPeak contains a fixed atmospheric model which is used to
236 convert barometric pressure into altitude. The model was
237 converted into a 469-element piece wise linear approximation
238 which is then used to compute the altitude of the ground and
239 apogee. The difference between these represents the maximum
240 height of the flight.
243 The model assumes a particular set of atmospheric conditions,
244 which while a reasonable average cannot represent the changing
245 nature of the real atmosphere. Fortunately, for flights
246 reasonably close to the ground, the effect of this global
247 inaccuracy are largely canceled out when the computed ground
248 altitude is subtracted from the computed apogee altitude, so
249 the resulting height is more accurate than either the ground
254 <title>Mechanical Considerations</title>
256 MicroPeak is designed to be rugged enough for typical rocketry
257 applications. It contains two moving parts, the battery holder
258 and the power switch, which were selected for their
262 The MicroPeak battery holder is designed to withstand impact
263 up to 150g without breaking contact (or, worse yet, causing
264 the battery to fall out). That means it should stand up to
265 almost any launch you care to try, and should withstand fairly
269 The power switch is designed to withstand up to 50g forces in
270 any direction. Because it is a sliding switch, orienting the
271 switch perpendicular to the direction of rocket travel will
272 serve to further protect the switch from launch forces.
277 <!-- LocalWords: Altusmetrum MicroPeak
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