1 <?xml version="1.0" encoding="utf-8" ?>
2 <!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
3 "/usr/share/xml/docbook/schema/dtd/4.5/docbookx.dtd">
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.
37 Thanks to John Lyngdal for suggesting that we build something like this.
40 Have fun using these products, and we hope to meet all of you
41 out on the rocket flight line somewhere.
44 NAR #87103, TRA #12201
47 NAR #88757, TRA #12200
52 <title>Quick Start Guide</title>
54 MicroPeak is designed to be easy to use. Requiring no external
55 components, flying takes just a few steps
60 Install the battery. Fit a CR1025 battery into the plastic
61 carrier. The positive (+) terminal should be towards the more
62 open side of the carrier. Slip the carrier into the battery
63 holder with the positive (+) terminal facing away from the
69 Install MicroPeak in your rocket. This can be as simple as
70 preparing a soft cushion of wadding inside a vented model payload
71 bay. Wherever you mount it, make sure you protect the
72 barometric sensor from corrosive ejection gasses as those
73 will damage the sensor.
78 Turn MicroPeak on. Slide the switch so that the actuator
79 covers the '1' printed on the board. MicroPeak will report
80 the maximum height of the last flight in decimeters using a
81 sequence of flashes on the LED. A sequence of short flashes
82 indicates one digit. A single long flash indicates zero. The
83 height is reported in decimeters, so the last digit will be
84 tenths of a meter. For example, if MicroPeak reports 5 4 4
85 3, then the maximum height of the last flight was 544.3m, or
91 Finish preparing the rocket for flight. After the
92 previous flight data have been reported, MicroPeak waits for
93 30 seconds before starting to check for launch. This gives
94 you time to finish assembling the rocket. As those
95 activities might cause pressure changes inside the airframe,
96 MicroPeak might accidentally detect boost. If you need to do
97 anything to the airframe after the 30 second window passes,
98 make sure to be careful not to disturb the altimeter. The
99 LED will remain dark during the 30 second delay, but after
100 that, it will start blinking once every 3 seconds.
105 Fly the rocket. Once the rocket passes about 10m in height
106 (32 feet), the micro-controller will record the ground
107 pressure and track the pressure seen during the flight. In
108 this mode, the LED flickers rapidly. When the rocket lands,
109 and the pressure stabilizes, the micro-controller will record
110 the minimum pressure pressure experienced during the flight,
111 compute the height represented by the difference in air
112 pressure and blink that value out on the LED. After that,
113 MicroPeak powers down to conserve battery power.
118 Recover the data. Turn MicroPeak off for a couple of seconds
119 (to discharge the capacitors) and then back on. MicroPeak
120 will blink out the maximum height for the last flight. Turn
121 MicroPeak back off to conserve battery power.
127 <title>Handling Precautions</title>
129 All Altus Metrum products are sophisticated electronic devices.
130 When handled gently and properly installed in an air-frame, they
131 will deliver impressive results. However, as with all electronic
132 devices, there are some precautions you must take.
135 The CR1025 Lithium batteries have an
136 extraordinary power density. This is great because we can fly with
137 much less battery mass... but if they are punctured
138 or their contacts are allowed to short, they can and will release their
140 Thus we recommend that you take some care when handling MicroPeak
141 to keep conductive material from coming in contact with the exposed metal elements.
144 The barometric sensors used in MicroPeak is
145 sensitive to sunlight. Please consider this when
146 designing an installation, for example, in an air-frame with a
147 see-through plastic payload bay. Many model rockets with payload bays
148 use clear plastic for the payload bay. Replacing these with an opaque
149 cardboard tube, painting them, or wrapping them with a layer of masking
150 tape are all reasonable approaches to keep the sensor out of direct
154 The barometric sensor sampling ports must be able to "breathe",
155 both by not being covered by foam or tape or other materials that might
156 directly block the hole on the top of the sensor, and also by having a
157 suitable static vent to outside air.
160 As with all other rocketry electronics, Altus Metrum altimeters must
161 be protected from exposure to corrosive motor exhaust and ejection
166 <title>Technical Information</title>
168 <title>Barometric Sensor</title>
170 MicroPeak uses the Measurement Specialties MS5607 sensor. This
171 has a range of 120kPa to 1kPa with an absolute accuracy of
172 150Pa and a resolution of 2.4Pa.
175 The pressure range corresponds roughly to an altitude range of
176 -1500m (-4900 feet) to 31000m (102000 feet), while the
177 resolution is approximately 20cm (8 inches) near sea level and
178 60cm (24in) at 10000m (33000 feet).
181 Ground pressure is computed from an average of 16 samples,
182 taken while the altimeter is at rest. Flight pressure is
183 computed from an exponential IIR filter designed to smooth out
184 transients caused by mechanical stress on the barometer.
188 <title>Micro-controller</title>
190 MicroPeak uses an Atmel ATtiny85 micro-controller. This tiny
191 CPU contains 8kB of flash for the application, 512B of RAM for
192 temporary data storage and 512B of EEPROM for non-volatile
193 storage of previous flight data.
196 The ATtiny85 has a low-power mode which turns off all of the
197 clocks and powers down most of the internal components. In
198 this mode, the chip consumes only .1μA of power. MicroPeak
199 uses this mode once the flight has ended to preserve battery
204 <title>Lithium Battery</title>
206 The CR1025 battery used by MicroPeak holes 30mAh of power,
207 which is sufficient to run for over 15 hours. Because
208 MicroPeak powers down on landing, run time includes only time
209 sitting on the launch pad or during flight.
212 The large positive terminal (+) is usually marked, while the
213 smaller negative terminal is not. Make sure you install the
214 battery with the positive terminal facing away from the
215 circuit board where it will be in contact with the metal
216 battery holder. A small pad on the circuit board makes contact
217 with the negative battery terminal.
220 Shipping restrictions prevent us from including a CR1025
221 battery with MicroPeak. Many stores carry CR1025 batteries as
222 they are commonly used in small electronic devices such as
227 <title>Atmospheric Model</title>
229 MicroPeak contains a fixed atmospheric model which is used to
230 convert barometric pressure into altitude. The model was
231 converted into a 469-element piece wise linear approximation
232 which is then used to compute the altitude of the ground and
233 apogee. The difference between these represents the maximum
234 height of the flight.
237 The model assumes a particular set of atmospheric conditions,
238 which while a reasonable average cannot represent the changing
239 nature of the real atmosphere. Fortunately, for flights
240 reasonably close to the ground, the effect of this global
241 inaccuracy are largely canceled out when the computed ground
242 altitude is subtracted from the computed apogee altitude, so
243 the resulting height is more accurate than either the ground
248 <title>Mechanical Considerations</title>
250 MicroPeak is designed to be rugged enough for typical rocketry
251 applications. It contains two moving parts, the battery holder
252 and the power switch, which were selected for their
256 The MicroPeak battery holder is designed to withstand impact
257 up to 150g without breaking contact (or, worse yet, causing
258 the battery to fall out). That means it should stand up to
259 almost any launch you care to try, and should withstand fairly
263 The power switch is designed to withstand up to 50g forces in
264 any direction. Because it is a sliding switch, orienting the
265 switch perpendicular to the direction of rocket travel will
266 serve to further protect the switch from launch forces.
271 <!-- LocalWords: Altusmetrum MicroPeak
projects / fw / altos / blob