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>
+ <revision>
+ <revnumber>1.1</revnumber>
+ <date>12 December 2012</date>
+ <revremark>
+ Add comments about EEPROM storage format and programming jig.
+ </revremark>
+ </revision>
</revhistory>
</bookinfo>
<acknowledgements>
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.
+ will damage the sensor, and shield it from light as that can
+ cause incorrect sensor readings.
</para>
</listitem>
<listitem>
</listitem>
<listitem>
<para>
- Recover the data. Turn MicroPeak off for a couple of seconds
- (to discharge the capacitors) and then back on. MicroPeak
+ 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>
to keep conductive material from coming in contact with the exposed metal elements.
</para>
<para>
- The barometric sensors used in MicroPeak is
- sensitive to sunlight. Please consider this when
- designing an installation, for example, in an air-frame with a
- see-through plastic payload bay. 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.
+ 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",
<title>Lithium Battery</title>
<para>
The CR1025 battery used by MicroPeak holes 30mAh of power,
- which is sufficient to run for over 15 hours. Because
+ 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>
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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