-<?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 recording altimeter for hobby rocketry</subtitle>
- <bookinfo>
- <author>
- <firstname>Keith</firstname>
- <surname>Packard</surname>
- </author>
- <copyright>
- <year>2014</year>
- <holder>Bdale Garbee and Keith Packard</holder>
- </copyright>
- <mediaobject>
- <imageobject>
- <imagedata fileref="micropeak-dime.jpg" width="6in"/>
- </imageobject>
- </mediaobject>
- <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>
- <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>
- <revision>
- <revnumber>1.3.2</revnumber>
- <date>12 February 2014</date>
- <revremark>
- Add a "Download" button to the main window, which makes it
- quicker to access the download function. Update the data
- download documentation to reflect the new MicroPeak USB
- adapter design. Monitor data during download to let you see
- if the USB connection is working at all by showing the
- characters received from the MicroPeak USB adapter.
- </revremark>
- </revision>
- </revhistory>
- </bookinfo>
- <dedication>
- <title>Acknowledgements</title>
- <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>
- </dedication>
- <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>
- <informalfigure>
- <mediaobject>
- <imageobject>
- <imagedata fileref="micropeak-back.jpg" width="4.5in"/>
- </imageobject>
- </mediaobject>
- </informalfigure>
- </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
- one minute 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 one minute window passes,
- make sure to be careful not to disturb the altimeter. The
- LED will remain dark during the one minute delay, but after
- that, it will start blinking once every 3 seconds.
- </para>
- </listitem>
- <listitem>
- <para>
- Fly the rocket. Once the rocket passes about 30m in height
- (100 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>The MicroPeak USB adapter</title>
- <informalfigure>
- <mediaobject>
- <imageobject>
- <imagedata fileref="MicroPeakUSB-2.0.jpg" width="4.5in"/>
- </imageobject>
- </mediaobject>
- </informalfigure>
- <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>
- Plug the MicroPeak USB adapter in to your computer.
- </para>
- </listitem>
- <listitem>
- <?dbfo keep-together="always"?>
- <para>
- Start the MicroPeak application.
- </para>
- <informalfigure>
- <mediaobject>
- <imageobject>
- <imagedata fileref="micropeak-nofont.svg" width="0.5in"/>
- </imageobject>
- </mediaobject>
- </informalfigure>
- </listitem>
- <listitem>
- <?dbfo keep-together="always"?>
- <para>
- Click on the Download button at the top of the window.
- </para>
- <informalfigure>
- <mediaobject>
- <imageobject>
- <imagedata fileref="micropeak-app.png" width="4.5in"/>
- </imageobject>
- </mediaobject>
- </informalfigure>
- </listitem>
- <listitem>
- <?dbfo keep-together="always"?>
- <para>
- Select from the listed devices. There will probably be
- only one.
- </para>
- <informalfigure>
- <mediaobject>
- <imageobject>
- <imagedata fileref="micropeak-device-dialog.png" width="2.3in"/>
- </imageobject>
- </mediaobject>
- </informalfigure>
- </listitem>
- <listitem>
- <para>
- The application will now wait until it receives valid data
- from the MicroPeak USB adapter.
- </para>
- <informalfigure>
- <mediaobject>
- <imageobject>
- <imagedata fileref="micropeak-download.png" width="2in"/>
- </imageobject>
- </mediaobject>
- </informalfigure>
- <para>
- The MicroPeak USB adapter has a small phototransistor
- under the hole in the center of the box.
- Locate this, turn on the MicroPeak and place the orange LED on the MicroPeak
- directly inside the hole, resting the MicroPeak itself on
- the box. You should see the blue LED on the MicroPeak USB
- adapter blinking in time with the orange LED on the
- MicroPeak board itself.
- </para>
- <informalfigure>
- <mediaobject>
- <imageobject>
- <imagedata fileref="MicroPeakUSB-2.0-inuse.jpg" width="4.5in"/>
- </imageobject>
- </mediaobject>
- </informalfigure>
- </listitem>
- <listitem>
- <?dbfo keep-together="always"?>
- <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>
- <informalfigure>
- <mediaobject>
- <imageobject>
- <imagedata fileref="micropeak-save-dialog.png" width="2.3in"/>
- </imageobject>
- </mediaobject>
- </informalfigure>
- </listitem>
- <listitem>
- <?dbfo keep-together="always"?>
- <para>
- Once the data are saved, a graph will be displayed with
- height, speed and acceleration values computed from the
- recorded barometric pressure data. See the next section
- for more details on that.
- </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>
- 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>
- <title>MicroPeak Graphs</title>
- <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>
- <informalfigure>
- <mediaobject>
- <imageobject>
- <imagedata fileref="micropeak-graph.png" width="4.5in"/>
- </imageobject>
- </mediaobject>
- </informalfigure>
- </section>
- <section>
- <title>MicroPeak Flight Statistics</title>
- <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>
- <informalfigure>
- <mediaobject>
- <imageobject>
- <imagedata fileref="micropeak-statistics.png" width="4.5in"/>
- </imageobject>
- </mediaobject>
- </informalfigure>
- </section>
- <section>
- <title>Raw Data</title>
- <para>
- A table consisting of the both the raw barometric pressure
- data and values computed from that for each recorded time.
- </para>
- <informalfigure>
- <mediaobject>
- <imageobject>
- <imagedata fileref="micropeak-raw-data.png" width="4.5in"/>
- </imageobject>
- </mediaobject>
- </informalfigure>
- </section>
- <section>
- <title>Configuring the Graph</title>
- <para>
- This selects which graph elements to show, and lets you
- switch between metric and imperial units
- </para>
- <informalfigure>
- <mediaobject>
- <imageobject>
- <imagedata fileref="micropeak-graph-configure.png" width="4.5in"/>
- </imageobject>
- </mediaobject>
- </informalfigure>
- </section>
- </section>
- <section>
- <title>Setting MicroPeak Preferences</title>
- <informalfigure>
- <mediaobject>
- <imageobject>
- <imagedata fileref="micropeak-preferences.png" width="1.8in"/>
- </imageobject>
- </mediaobject>
- </informalfigure>
- <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>
- <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. The flight pressure used to
- report maximum height is computed from a Kalman filter
- designed to smooth out any minor noise in the sensor
- values. The flight pressure recorded to non-volatile storage
- is unfiltered, coming directly from the pressure sensor.
- </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 holds 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 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>
- <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>
- <para>
- Because the raw pressure data is recorded to non-volatile
- storage, you can use that, along with a more sophisticated
- atmospheric model, to compute your own altitude values.
- </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>
- <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 is the
- information captured with the MicroPeak USB adapter. It can
- also be read 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>
-<!-- LocalWords: Altusmetrum MicroPeak
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