MicroPeak Owner's Manual

A peak-recording altimeter for hobby rocketry

Keith Packard

+MicroPeak Owner's Manual

MicroPeak Owner's Manual

A recording altimeter for hobby rocketry

Keith Packard

This document is released under the terms of the Creative Commons ShareAlike 3.0 @@ -6,7 +6,15 @@ license.

Revision History
Revision 0.1	29 October 2012
Initial release with preliminary hardware. -

Acknowledgements

+ Revision 1.018 November 2012 + Updates for version 1.0 release. + Revision 1.112 December 2012 + Add comments about EEPROM storage format and programming jig. + Revision 1.220 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.

@@ -21,7 +29,7 @@ Keith NAR #88757, TRA #12200

Table of Contents

1. Quick Start Guide

2. Handling Precautions

3. Technical Information

1. Barometric Sensor
2. Micro-controller
3. Lithium Battery
4. Atmospheric Model
5. Mechanical Considerations

Chapter 1. Quick Start Guide

Table of Contents

1. Quick Start Guide

2. Handling Precautions

3. The MicroPeak USB adapter

1. Installing the MicroPeak software
2. Downloading Micro Peak data
3. Analyzing MicroPeak Data
4. Configuring the MicroPeak application

4. Technical Information

1. Barometric Sensor
2. Micro-controller
3. Lithium Battery
4. Atmospheric Model
5. Mechanical Considerations
6. On-board data storage
7. MicroPeak Programming Interface

List of Tables

4.1. MicroPeak EEPROM Data Storage

Chapter 1. Quick Start Guide

MicroPeak is designed to be easy to use. Requiring no external components, flying takes just a few steps

@@ -35,7 +43,8 @@ NAR 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.
Turn MicroPeak on. Slide the switch so that the actuator covers the '1' printed on the board. MicroPeak will report @@ -68,11 +77,10 @@ NAR pressure and blink that value out on the LED. After that, MicroPeak powers down to conserve battery power.
- 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. -

Chapter 2. 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 @@ -86,14 +94,13 @@ NAR 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 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.

The barometric sensor sampling ports must be able to "breathe", both by not being covered by foam or tape or other materials that might @@ -103,7 +110,119 @@ NAR As with all other rocketry electronics, Altus Metrum altimeters must be protected from exposure to corrosive motor exhaust and ejection charge gasses. -

Chapter 3. Technical Information

Table of Contents

1. Barometric Sensor
2. Micro-controller
3. Lithium Battery
4. Atmospheric Model
5. Mechanical Considerations

1. Barometric Sensor

Chapter 3. The MicroPeak USB adapter

Table of Contents

1. Installing the MicroPeak software
2. Downloading Micro Peak data
3. Analyzing MicroPeak Data
4. Configuring the MicroPeak application

+ 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. +

1. 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/AltOS. +

+ 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. +

2. 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 right over + 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. +

3. 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. +

4. 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. +

Chapter 4. Technical Information

Table of Contents

1. Barometric Sensor
2. Micro-controller
3. Lithium Battery
4. Atmospheric Model
5. Mechanical Considerations
6. On-board data storage
7. MicroPeak Programming Interface

1. 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. @@ -115,9 +234,9 @@ NAR

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. -

2. Micro-controller

+ computed from a Kalman filter designed to smooth out any minor + noise in the sensor values. +

2. 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 @@ -128,9 +247,9 @@ NAR this mode, the chip consumes only .1μA of power. MicroPeak uses this mode once the flight has ended to preserve battery power. -

3. Lithium Battery

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.

@@ -141,11 +260,11 @@ NAR battery holder. A small pad on the circuit board makes contact 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. -

4. Atmospheric Model

+ 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. +

4. 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 @@ -161,7 +280,7 @@ NAR altitude is subtracted from the computed apogee altitude, so the resulting height is more accurate than either the ground or apogee altitudes. -

5. 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 @@ -177,4 +296,65 @@ NAR 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. +

6. 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. +

Table 4.1. 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. +

7. 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.

diff --git a/AltOS/doc/micropeak.pdf b/AltOS/doc/micropeak.pdf index 63aece9..3dd1476 100644 Binary files a/AltOS/doc/micropeak.pdf and b/AltOS/doc/micropeak.pdf differ diff --git a/MicroPeak/index.mdwn b/MicroPeak/index.mdwn index 05e432e..b98b8eb 100644 --- a/MicroPeak/index.mdwn +++ b/MicroPeak/index.mdwn @@ -19,6 +19,23 @@ The MicroPeak manual is available in [html](../AltOS/doc/micropeak.html) and [pdf](../AltOS/doc/micropeak.pdf) formats. +## Software ## + +The MicroPeak application runs on Linux, Mac OS X and Windows. It +communicates with the MicroPeak USB adapter to download and analyze +flight data. It's written in [Java](http://java.com) and offers the +same functionality and interface on all three platforms. It uses the +FTDI USB Serial drivers to communicate with the hardware. If you're +running Mac OS X or Windows, a compatible version of those drivers is +included with the software. You can also install a different from from +the [FTDI Driver](http://www.ftdichip.com/FTDrivers.htm) page. + +### Latest version ### + + * [Windows](releases/1.2/MicroPeak-Windows-1-1-9-3.exe) + * [Linux](releases/1.2/MicroPeak-Linux-1.1.9.3.tar.bz2) + * [Mac OS X](releases/1.2/MicroPeak-Mac-1.1.9.3.dmg) + ## Hardware Features ## * Measure ground pressure and peak altitude pressure. diff --git a/MicroPeak/releases/1.2/MicroPeak-Linux-1.1.9.3.tar.bz2 b/MicroPeak/releases/1.2/MicroPeak-Linux-1.1.9.3.tar.bz2 new file mode 100644 index 0000000..ff6c0f4 Binary files /dev/null and b/MicroPeak/releases/1.2/MicroPeak-Linux-1.1.9.3.tar.bz2 differ diff --git a/MicroPeak/releases/1.2/MicroPeak-Mac-1.1.9.3.dmg b/MicroPeak/releases/1.2/MicroPeak-Mac-1.1.9.3.dmg new file mode 100644 index 0000000..5f206dc Binary files /dev/null and b/MicroPeak/releases/1.2/MicroPeak-Mac-1.1.9.3.dmg differ diff --git a/MicroPeak/releases/1.2/MicroPeak-Windows-1-1-9-3.exe b/MicroPeak/releases/1.2/MicroPeak-Windows-1-1-9-3.exe new file mode 100644 index 0000000..aa1c974 Binary files /dev/null and b/MicroPeak/releases/1.2/MicroPeak-Windows-1-1-9-3.exe differ