X-Git-Url: https://git.gag.com/?p=fw%2Faltos;a=blobdiff_plain;f=doc%2Fmicropeak.xsl;h=afa6fd1575fdba714407535d2610c239d5b904ab;hp=284d0fb04a359ff11e7b3f865d9dee5b7f841f78;hb=f9bbca59a9034cf7e6df4577e627d7447f3a9d51;hpb=ceea0e75ac42acac4a20bf88f34bb93fd2768f4c diff --git a/doc/micropeak.xsl b/doc/micropeak.xsl index 284d0fb0..afa6fd15 100644 --- a/doc/micropeak.xsl +++ b/doc/micropeak.xsl @@ -3,7 +3,7 @@ "/usr/share/xml/docbook/schema/dtd/4.5/docbookx.dtd"> MicroPeak Owner's Manual - A peak-recording altimeter for hobby rocketry + A recording altimeter for hobby rocketry Keith @@ -37,9 +37,26 @@ Updates for version 1.0 release. + + 1.1 + 12 December 2012 + + Add comments about EEPROM storage format and programming jig. + + + + 1.2 + 20 January 2013 + + Add documentation for the MicroPeak USB adapter board. Note + the switch to a Kalman filter for peak altitude + determination. + + - + + Acknowledgements Thanks to John Lyngdal for suggesting that we build something like this. @@ -54,7 +71,7 @@ Keith Packard, KD7SQG NAR #88757, TRA #12200 - + Quick Start Guide @@ -168,6 +185,181 @@ NAR #88757, TRA #12200 charge gasses. + + The MicroPeak USB adapter + + 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 + . + + + 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 . + +
+
+ Downloading Micro Peak data + + + + Connect the MicroPeak USB adapter to a USB cable and plug it + in to your computer. + + + + + Start the MicroPeak application, locate the File menu and + select the Download entry. + + + + + 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. + + + + + 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. + + + +
+
+ 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. + + + 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. + + + 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. + + + A table consisting of the both the raw barometric pressure + data and values computed from that for each recorded time. + + + 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. + +
+
+ Configuring the MicroPeak application + + The MicroPeak application has a few user settings which are + configured through the Preferences dialog, which can be + accessed from the File menu. + + + + 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. + + + + + 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. + + + + + 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. + + + + + 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. + + + + + 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. + +
+ Technical Information
@@ -186,8 +378,8 @@ NAR #88757, TRA #12200 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.
@@ -223,10 +415,10 @@ NAR #88757, TRA #12200 with the negative battery terminal. - 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.
@@ -272,6 +464,118 @@ NAR #88757, TRA #12200 serve to further protect the switch from launch forces.
+
+ 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 information can + be extracted from MicroPeak through any AVR programming + tool. + + + MicroPeak EEPROM Data Storage + + + + + + + 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. + +
+
+ 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. + +