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-<?xml version="1.0" encoding="utf-8" ?>
-<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
- "/usr/share/xml/docbook/schema/dtd/4.5/docbookx.dtd">
-<book>
- <title>MicroPeak Owner's Manual</title>
- <subtitle>A peak-recording altimeter for hobby rocketry</subtitle>
- <bookinfo>
- <author>
- <firstname>Keith</firstname>
- <surname>Packard</surname>
- </author>
- <copyright>
- <year>2012</year>
- <holder>Bdale Garbee and Keith Packard</holder>
- </copyright>
- <legalnotice>
- <para>
- This document is released under the terms of the
- <ulink url="http://creativecommons.org/licenses/by-sa/3.0/">
- Creative Commons ShareAlike 3.0
- </ulink>
- license.
- </para>
- </legalnotice>
- <revhistory>
- <revision>
- <revnumber>0.1</revnumber>
- <date>29 October 2012</date>
- <revremark>
- Initial release with preliminary hardware.
- </revremark>
- </revision>
- <revision>
- <revnumber>1.0</revnumber>
- <date>18 November 2012</date>
- <revremark>
- Updates for version 1.0 release.
- </revremark>
- </revision>
- </revhistory>
- </bookinfo>
- <acknowledgements>
- <para>
- Thanks to John Lyngdal for suggesting that we build something like this.
- </para>
- <para>
- Have fun using these products, and we hope to meet all of you
- out on the rocket flight line somewhere.
- <literallayout>
-Bdale Garbee, KB0G
-NAR #87103, TRA #12201
-
-Keith Packard, KD7SQG
-NAR #88757, TRA #12200
- </literallayout>
- </para>
- </acknowledgements>
- <chapter>
- <title>Quick Start Guide</title>
- <para>
- MicroPeak is designed to be easy to use. Requiring no external
- components, flying takes just a few steps
- </para>
- <itemizedlist>
- <listitem>
- <para>
- Install the battery. Fit a CR1025 battery into the plastic
- carrier. The positive (+) terminal should be towards the more
- open side of the carrier. Slip the carrier into the battery
- holder with the positive (+) terminal facing away from the
- circuit board.
- </para>
- </listitem>
- <listitem>
- <para>
- Install MicroPeak in your rocket. This can be as simple as
- preparing a soft cushion of wadding inside a vented model payload
- bay. Wherever you mount it, make sure you protect the
- barometric sensor from corrosive ejection gasses as those
- will damage the sensor, and shield it from light as that can
- cause incorrect sensor readings.
- </para>
- </listitem>
- <listitem>
- <para>
- Turn MicroPeak on. Slide the switch so that the actuator
- covers the '1' printed on the board. MicroPeak will report
- the maximum height of the last flight in decimeters using a
- sequence of flashes on the LED. A sequence of short flashes
- indicates one digit. A single long flash indicates zero. The
- height is reported in decimeters, so the last digit will be
- tenths of a meter. For example, if MicroPeak reports 5 4 4
- 3, then the maximum height of the last flight was 544.3m, or
- 1786 feet.
- </para>
- </listitem>
- <listitem>
- <para>
- Finish preparing the rocket for flight. After the
- previous flight data have been reported, MicroPeak waits for
- 30 seconds before starting to check for launch. This gives
- you time to finish assembling the rocket. As those
- activities might cause pressure changes inside the airframe,
- MicroPeak might accidentally detect boost. If you need to do
- anything to the airframe after the 30 second window passes,
- make sure to be careful not to disturb the altimeter. The
- LED will remain dark during the 30 second delay, but after
- that, it will start blinking once every 3 seconds.
- </para>
- </listitem>
- <listitem>
- <para>
- Fly the rocket. Once the rocket passes about 10m in height
- (32 feet), the micro-controller will record the ground
- pressure and track the pressure seen during the flight. In
- this mode, the LED flickers rapidly. When the rocket lands,
- and the pressure stabilizes, the micro-controller will record
- the minimum pressure pressure experienced during the flight,
- compute the height represented by the difference in air
- pressure and blink that value out on the LED. After that,
- MicroPeak powers down to conserve battery power.
- </para>
- </listitem>
- <listitem>
- <para>
- Recover the data. Turn MicroPeak off and then back on. MicroPeak
- will blink out the maximum height for the last flight. Turn
- MicroPeak back off to conserve battery power.
- </para>
- </listitem>
- </itemizedlist>
- </chapter>
- <chapter>
- <title>Handling Precautions</title>
- <para>
- All Altus Metrum products are sophisticated electronic devices.
- When handled gently and properly installed in an air-frame, they
- will deliver impressive results. However, as with all electronic
- devices, there are some precautions you must take.
- </para>
- <para>
- The CR1025 Lithium batteries have an
- extraordinary power density. This is great because we can fly with
- much less battery mass... but if they are punctured
- or their contacts are allowed to short, they can and will release their
- energy very rapidly!
- Thus we recommend that you take some care when handling MicroPeak
- to keep conductive material from coming in contact with the exposed metal elements.
- </para>
- <para>
- The barometric sensor used in MicroPeak is sensitive to
- sunlight. Please consider this when designing an
- installation. Many model rockets with payload bays use clear
- plastic for the payload bay. Replacing these with an opaque
- cardboard tube, painting them, or wrapping them with a layer of
- masking tape are all reasonable approaches to keep the sensor
- out of direct sunlight.
- </para>
- <para>
- The barometric sensor sampling ports must be able to "breathe",
- both by not being covered by foam or tape or other materials that might
- directly block the hole on the top of the sensor, and also by having a
- suitable static vent to outside air.
- </para>
- <para>
- As with all other rocketry electronics, Altus Metrum altimeters must
- be protected from exposure to corrosive motor exhaust and ejection
- charge gasses.
- </para>
- </chapter>
- <chapter>
- <title>Technical Information</title>
- <section>
- <title>Barometric Sensor</title>
- <para>
- MicroPeak uses the Measurement Specialties MS5607 sensor. This
- has a range of 120kPa to 1kPa with an absolute accuracy of
- 150Pa and a resolution of 2.4Pa.
- </para>
- <para>
- The pressure range corresponds roughly to an altitude range of
- -1500m (-4900 feet) to 31000m (102000 feet), while the
- resolution is approximately 20cm (8 inches) near sea level and
- 60cm (24in) at 10000m (33000 feet).
- </para>
- <para>
- Ground pressure is computed from an average of 16 samples,
- taken while the altimeter is at rest. Flight pressure is
- computed from an exponential IIR filter designed to smooth out
- transients caused by mechanical stress on the barometer.
- </para>
- </section>
- <section>
- <title>Micro-controller</title>
- <para>
- MicroPeak uses an Atmel ATtiny85 micro-controller. This tiny
- CPU contains 8kB of flash for the application, 512B of RAM for
- temporary data storage and 512B of EEPROM for non-volatile
- storage of previous flight data.
- </para>
- <para>
- The ATtiny85 has a low-power mode which turns off all of the
- clocks and powers down most of the internal components. In
- this mode, the chip consumes only .1μA of power. MicroPeak
- uses this mode once the flight has ended to preserve battery
- power.
- </para>
- </section>
- <section>
- <title>Lithium Battery</title>
- <para>
- The CR1025 battery used by MicroPeak holes 30mAh of power,
- which is sufficient to run for over 40 hours. Because
- MicroPeak powers down on landing, run time includes only time
- sitting on the launch pad or during flight.
- </para>
- <para>
- The large positive terminal (+) is usually marked, while the
- smaller negative terminal is not. Make sure you install the
- battery with the positive terminal facing away from the
- circuit board where it will be in contact with the metal
- battery holder. A small pad on the circuit board makes contact
- with the negative battery terminal.
- </para>
- <para>
- Shipping restrictions prevent us from including a CR1025
- battery with MicroPeak. Many stores carry CR1025 batteries as
- they are commonly used in small electronic devices such as
- flash lights.
- </para>
- </section>
- <section>
- <title>Atmospheric Model</title>
- <para>
- MicroPeak contains a fixed atmospheric model which is used to
- convert barometric pressure into altitude. The model was
- converted into a 469-element piece wise linear approximation
- which is then used to compute the altitude of the ground and
- apogee. The difference between these represents the maximum
- height of the flight.
- </para>
- <para>
- The model assumes a particular set of atmospheric conditions,
- which while a reasonable average cannot represent the changing
- nature of the real atmosphere. Fortunately, for flights
- reasonably close to the ground, the effect of this global
- inaccuracy are largely canceled out when the computed ground
- altitude is subtracted from the computed apogee altitude, so
- the resulting height is more accurate than either the ground
- or apogee altitudes.
- </para>
- </section>
- <section>
- <title>Mechanical Considerations</title>
- <para>
- MicroPeak is designed to be rugged enough for typical rocketry
- applications. It contains two moving parts, the battery holder
- and the power switch, which were selected for their
- ruggedness.
- </para>
- <para>
- The MicroPeak battery holder is designed to withstand impact
- up to 150g without breaking contact (or, worse yet, causing
- the battery to fall out). That means it should stand up to
- almost any launch you care to try, and should withstand fairly
- rough landings.
- </para>
- <para>
- The power switch is designed to withstand up to 50g forces in
- any direction. Because it is a sliding switch, orienting the
- switch perpendicular to the direction of rocket travel will
- serve to further protect the switch from launch forces.
- </para>
- </section>
- </chapter>
-</book>
-<!-- LocalWords: Altusmetrum MicroPeak
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