--- /dev/null
+= MicroPeak Owner's Manual
+:doctype: book
+:numbered:
+
+[dedication]
+== Acknowledgements
+
+ Thanks to John Lyngdal for suggesting that we build something
+ like this.
+
+ Have fun using these products, and we hope to meet all of you
+ out on the rocket flight line somewhere.
+
+ [verse]
+ Bdale Garbee, KB0G
+ NAR #87103, TRA #12201
+
+ [verse]
+ Keith Packard, KD7SQG
+ NAR #88757, TRA #12200
+
+== Using MicroPeak
+
+ MicroPeak is designed to be easy to use. Requiring no external
+ components, flying takes just a few steps
+
+ * 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.
+
+ .MicroPeak and Battery
+ image::micropeak-back.jpg[width="4.5in"]
+
+ * 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.
+
+ * 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.
+
+ * 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.
+
+ * 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.
+
+ * 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.
+
+== The MicroPeak USB adapter
+
+ .MicroPeak USB Adapter
+ image::MicroPeakUSB-2.0.jpg[width="4.5in"]
+
+ 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.
+
+ === Installing the MicroPeak software
+
+ The MicroPeak application runs on Linux, Mac OS X and
+ Windows. You can download the latest version from
+ http://altusmetrum.org/MicroPeak
+
+ 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
+ http://www.ftdichip.com/FTDrivers.htm
+
+ === Downloading Micro Peak data
+
+ * Plug the MicroPeak USB adapter in to your computer.
+
+ * Start the MicroPeak application.
+
+ image::micropeak-nofont.svg[width="0.5in"]
+
+ * Click on the Download button at the top of the
+ window.
+
+ .MicroPeak Application
+ image::micropeak-app.png[width="4.5in"]
+
+ * Select from the listed devices. There will probably
+ be only one.
+
+ .MicroPeak Device Dialog
+ image::micropeak-device-dialog.png[width="2.3in"]
+
+ * The application will now wait until it receives
+ valid data from the MicroPeak USB adapter.
+
+ .MicroPeak Download Dialog
+ image::micropeak-download.png[width="2in"]
+
+ * 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.
+
+ .MicroPeak Downloading
+ image::MicroPeakUSB-2.0-inuse.jpg[width="4.5in"]
+
+ * 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.
+
+ .MicroPeak Save Dialog
+ image::micropeak-save-dialog.png[width="2.3in"]
+
+ * 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.
+
+ === Analyzing MicroPeak Data
+
+ The MicroPeak application can present flight data in
+ the form of a graph, a collection of computed
+ statistics or in tabular form.
+
+ 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.
+
+ 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.
+
+ 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.
+
+ ==== MicroPeak Graphs
+
+ .MicroPeak Graph
+ image::micropeak-graph.png[width="4.5in"]
+
+ 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.
+
+ ==== MicroPeak Flight Statistics
+
+ .MicroPeak Flight Statistics
+ image::micropeak-statistics.png[width="4.5in"]
+
+ 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.
+
+ ==== Raw Flight Data
+
+ .MicroPeak Raw Flight Data
+ image::micropeak-raw-data.png[width="4.5in"]
+
+ A table consisting of the both the raw barometric pressure
+ data and values computed from that for each recorded time.
+
+ ==== Configuring the Graph
+
+ .MicroPeak Graph Configuration
+ image::micropeak-graph-configure.png[width="4.5in"]
+
+ This selects which graph elements to show, and lets you
+ switch between metric and imperial units
+
+ === Setting MicroPeak Preferences
+
+ .MicroPeak Preferences
+ image::micropeak-preferences.png[width="1.8in"]
+
+ The MicroPeak application has a few user settings which are
+ configured through the Preferences dialog, which can be
+ accessed from the File menu.
+
+ Log Directory::
+
+ 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.
+
+ Imperial Units::
+
+ 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.
+
+ Serial Debug::
+
+ 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.
+
+ Font Size::
+
+ 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.
+
+ Look & Feel::
+
+ 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.
+
+ 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.
+
+[appendix]
+== Handling Precautions
+
+ 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.
+
+ [WARNING]
+
+ 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.
+
+ 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.
+
+ 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.
+
+ As with all other rocketry electronics, Altus Metrum
+ altimeters must be protected from exposure to corrosive motor
+ exhaust and ejection charge gasses.
+
+[appendix]
+== Technical Information
+
+ === Barometric Sensor
+
+ 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.
+
+ 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).
+
+ 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.
+
+ === Micro-controller
+
+ 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.
+
+ 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.
+
+ === Lithium Battery
+
+ 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.
+
+ 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.
+
+ 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.
+
+ === Atmospheric Model
+
+ 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.
+
+ 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.
+
+ 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.
+
+ === Mechanical Considerations
+
+ 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.
+
+ 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.
+
+ 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.
+
+ === MicroPeak Programming Interface
+
+ 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.
+
+ 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.
+
+ 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.
+
+ 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.
+
+[appendix]
+== On-board data storage
+
+ 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.
+
+ 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.
+
+
+ .MicroPeak EEPROM Data Storage
+ [options="border",cols="2,1,7"]
+ |====
+ |Address |Size (bytes) |Description
+ |0x000 |4 |Average ground pressure (Pa)
+ |0x004 |4 |Minimum flight pressure (Pa)
+ |0x008 |2 |Number of in-flight samples
+ |0x00a … 0x1fe |2 |Instantaneous flight pressure (Pa) low 16 bits
+ |====
+
+ 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 *not* 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.
+
+ 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.
projects / fw / altos / blobdiff