"/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>
+ <subtitle>A recording altimeter for hobby rocketry</subtitle>
<bookinfo>
<author>
<firstname>Keith</firstname>
Updates for version 1.0 release.
</revremark>
</revision>
+ <revision>
+ <revnumber>1.1</revnumber>
+ <date>12 December 2012</date>
+ <revremark>
+ Add comments about EEPROM storage format and programming jig.
+ </revremark>
+ </revision>
+ <revision>
+ <revnumber>1.2</revnumber>
+ <date>20 January 2013</date>
+ <revremark>
+ Add documentation for the MicroPeak USB adapter board. Note
+ the switch to a Kalman filter for peak altitude
+ determination.
+ </revremark>
+ </revision>
</revhistory>
</bookinfo>
- <acknowledgements>
+ <dedication>
+ <title>Acknowledgements</title>
<para>
Thanks to John Lyngdal for suggesting that we build something like this.
</para>
NAR #88757, TRA #12200
</literallayout>
</para>
- </acknowledgements>
+ </dedication>
<chapter>
<title>Quick Start Guide</title>
<para>
charge gasses.
</para>
</chapter>
+ <chapter>
+ <title>The MicroPeak USB adapter</title>
+ <para>
+ MicroPeak stores barometric pressure information for the first
+ 48 seconds of the flight in on-board non-volatile memory. The
+ contents of this memory can be downloaded to a computer using
+ the MicroPeak USB adapter.
+ </para>
+ <section>
+ <title>Installing the MicroPeak software</title>
+ <para>
+ The MicroPeak application runs on Linux, Mac OS X and
+ Windows. You can download the latest version from
+ <ulink url="http://altusmetrum.org/AltOS"/>.
+ </para>
+ <para>
+ On Mac OS X and Windows, the FTDI USB device driver needs to
+ be installed. A compatible version of this driver is included
+ with the MicroPeak application, but you may want to download a
+ newer version from <ulink
+ url="http://www.ftdichip.com/FTDrivers.htm"/>.
+ </para>
+ </section>
+ <section>
+ <title>Downloading Micro Peak data</title>
+ <itemizedlist>
+ <listitem>
+ <para>
+ Connect the MicroPeak USB adapter to a USB cable and plug it
+ in to your computer.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ Start the MicroPeak application, locate the File menu and
+ select the Download entry.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ The MicroPeak USB adapter has a small phototransistor on
+ the end of the board furthest from the USB
+ connector. Locate this and place the LED on the MicroPeak
+ directly in contact with it. The MicroPeak LED and the
+ MicroPeak USB adapter photo need to be touching—even a
+ millimeters of space between them will reduce the light
+ intensity from the LED enough that the phototransistor
+ will not sense it. Turn on the MicroPeak board and adjust
+ the position until the blue LED on the MicroPeak USB
+ adapter blinks in time with the orange LED on the
+ MicroPeak board.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ After the maximum flight height is reported, MicroPeak will
+ pause for a few seconds, blink the LED four times rapidly
+ and then send the data in one long blur on the LED. The
+ MicroPeak application should receive the data. When it does,
+ it will present the data in a graph and offer to save the
+ data to a file. If not, you can power cycle the MicroPeak
+ board and try again.
+ </para>
+ </listitem>
+ </itemizedlist>
+ </section>
+ <section>
+ <title>Analyzing MicroPeak Data</title>
+ <para>
+ The MicroPeak application can present flight data in the form
+ of a graph, a collection of computed statistics or in tabular
+ form.
+ </para>
+ <para>
+ MicroPeak collects raw barometric pressure data which is
+ then used to compute the remaining data. Altitude is computed
+ through a standard atmospheric model. Absolute error in this
+ data will be affected by local atmospheric
+ conditions. Fortunately, these errors tend to mostly cancel
+ out, so the error in the height computation is much smaller
+ than the error in altitude would be.
+ </para>
+ <para>
+ Speed and acceleration are computed by first smoothing the
+ height data with a Gaussian window averaging filter. For speed
+ data, this average uses seven samples. For acceleration data,
+ eleven samples are used. These were chosen to provide
+ reasonably smooth speed and acceleration data, which would
+ otherwise be swamped with noise.
+ </para>
+ <para>
+ Under the Graph tab, the height, speed and acceleration values
+ are displayed together. You can zoom in on the graph by
+ clicking and dragging to sweep out an area of
+ interest. Right-click on the plot to bring up a menu that will
+ let you save, copy or print the graph.
+ </para>
+ <para>
+ The Statistics tab presents overall data from the flight. Note
+ that the Maximum height value is taken from the minumum
+ pressure captured in flight, and may be different from the
+ apparant apogee value as the on-board data are sampled twice
+ as fast as the recorded values, or because the true apogee
+ occurred after the on-board memory was full. Each value is
+ presented in several units as appropriate.
+ </para>
+ <para>
+ A table consisting of the both the raw barometric pressure
+ data and values computed from that for each recorded time.
+ </para>
+ <para>
+ The File menu has operations to open existing flight logs,
+ Download new data from MicroPeak, Save a copy of the flight
+ log to a new file, Export the tabular data (as seen in the Raw
+ Data tab) to a file, change the application Preferences, Close
+ the current window or close all windows and Exit the
+ application.
+ </para>
+ </section>
+ <section>
+ <title>Configuring the MicroPeak application</title>
+ <para>
+ The MicroPeak application has a few user settings which are
+ configured through the Preferences dialog, which can be
+ accessed from the File menu.
+ <itemizedlist>
+ <listitem>
+ <para>
+ The Log Directory is where flight data will be saved to
+ and loaded from by default. Of course, you can always
+ navigate to other directories in the file chooser windows,
+ this setting is just the starting point.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ If you prefer to see your graph data in feet and
+ miles per hour instead of meters and meters per second,
+ you can select Imperial Units.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ To see what data is actually arriving over the serial
+ port, start the MicroPeak application from a command
+ prompt and select the Serial Debug option. This can be
+ useful in debugging serial communication problems, but
+ most people need never choose this.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ You can adjust the size of the text in the Statistics tab
+ by changing the Font size preference. There are three
+ settings, with luck one will both fit on your screen and
+ provide readable values.
+ </para>
+ </listitem>
+ <listitem>
+ <para>
+ The Look & feel menu shows a list of available
+ application appearance choices. By default, the MicroPeak
+ application tries to blend in with other applications, but
+ you may choose some other appearance if you like.
+ </para>
+ </listitem>
+ </itemizedlist>
+ </para>
+ <para>
+ Note that MicroPeak shares a subset of the AltosUI
+ preferences, so if you use both of these applications, change
+ in one application will affect the other.
+ </para>
+ </section>
+ </chapter>
<chapter>
<title>Technical Information</title>
<section>
<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.
+ computed from a Kalman filter designed to smooth out any minor
+ noise in the sensor values.
</para>
</section>
<section>
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.
+ Shipping restrictions may prevent us from including a CR1025
+ battery with MicroPeak. If so, many stores carry CR1025
+ batteries as they are commonly used in small electronic
+ devices such as flash lights.
</para>
</section>
<section>
serve to further protect the switch from launch forces.
</para>
</section>
+ <section>
+ <title>On-board data storage</title>
+ <para>
+ The ATtiny85 has 512 bytes of non-volatile storage, separate
+ from the code storage memory. The MicroPeak firmware uses this
+ to store information about the last completed
+ flight. Barometric measurements from the ground before launch
+ and at apogee are stored, and used at power-on to compute the
+ height of the last flight.
+ </para>
+ <para>
+ In addition to the data used to present the height of the last
+ flight, MicroPeak also stores barometric information sampled
+ at regular intervals during the flight. This information can
+ be extracted from MicroPeak through any AVR programming
+ tool.
+ </para>
+ <table frame='all'>
+ <title>MicroPeak EEPROM Data Storage</title>
+ <tgroup cols='3' align='center' colsep='1' rowsep='1'>
+ <colspec align='center' colwidth='2*' colname='Address'/>
+ <colspec align='center' colwidth='*' colname='Size (bytes)'/>
+ <colspec align='left' colwidth='7*' colname='Description'/>
+ <thead>
+ <row>
+ <entry align='center'>Address</entry>
+ <entry align='center'>Size (bytes)</entry>
+ <entry align='center'>Description</entry>
+ </row>
+ </thead>
+ <tbody>
+ <row>
+ <entry>0x000</entry>
+ <entry>4</entry>
+ <entry>Average ground pressure (Pa)</entry>
+ </row>
+ <row>
+ <entry>0x004</entry>
+ <entry>4</entry>
+ <entry>Minimum flight pressure (Pa)</entry>
+ </row>
+ <row>
+ <entry>0x008</entry>
+ <entry>2</entry>
+ <entry>Number of in-flight samples</entry>
+ </row>
+ <row>
+ <entry>0x00a … 0x1fe</entry>
+ <entry>2</entry>
+ <entry>Instantaneous flight pressure (Pa) low 16 bits</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+ <para>
+ All EEPROM data are stored least-significant byte first. The
+ instantaneous flight pressure data are stored without the
+ upper 16 bits of data. The upper bits can be reconstructed
+ from the previous sample, assuming that pressure doesn't
+ change by more more than 32kPa in a single sample
+ interval. Note that this pressure data is <emphasis>not</emphasis>
+ filtered in any way, while both the recorded ground and apogee
+ pressure values are, so you shouldn't expect the minimum
+ instantaneous pressure value to match the recorded minimum
+ pressure value exactly.
+ </para>
+ <para>
+ MicroPeak samples pressure every 96ms, but stores only every
+ other sample in the EEPROM. This provides for 251 pressure
+ samples at 192ms intervals, or 48.192s of storage. The clock
+ used for these samples is a factory calibrated RC circuit
+ built into the ATtiny85 and is accurate only to within ±10% at
+ 25°C. So, you can count on the pressure data being accurate,
+ but speed or acceleration data computed from this will be
+ limited by the accuracy of this clock.
+ </para>
+ </section>
+ <section>
+ <title>MicroPeak Programming Interface</title>
+ <para>
+ MicroPeak exposes a standard 6-pin AVR programming interface,
+ but not using the usual 2x3 array of pins on 0.1"
+ centers. Instead, there is a single row of tiny 0.60mm ×
+ 0.85mm pads on 1.20mm centers exposed near the edge of the
+ circuit board. We couldn't find any connector that was
+ small enough to include on the circuit board.
+ </para>
+ <para>
+ In lieu of an actual connector, the easiest way to connect to
+ the bare pads is through a set of Pogo pins. These
+ spring-loaded contacts are designed to connect in precisely
+ this way. We've designed a programming jig, the MicroPeak
+ Pogo Pin board which provides a standard AVR interface on one
+ end and a recessed slot for MicroPeak to align the board with
+ the Pogo Pins.
+ </para>
+ <para>
+ The MicroPeak Pogo Pin board is not a complete AVR programmer,
+ it is an interface board that provides a 3.3V regulated power
+ supply to run the MicroPeak via USB and a standard 6-pin AVR
+ programming interface with the usual 2x3 grid of pins on 0.1"
+ centers. This can be connected to any AVR programming
+ dongle.
+ </para>
+ <para>
+ The AVR programming interface cannot run faster than ¼ of the
+ AVR CPU clock frequency. Because MicroPeak runs at 250kHz to
+ save power, you must configure your AVR programming system to
+ clock the AVR programming interface at no faster than
+ 62.5kHz, or a clock period of 32µS.
+ </para>
+ </section>
</chapter>
</book>
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