MicroPeak Owner's Manual

A 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 license. -

Revision History

Revision 0.1

29 October 2012

Revision History
Revision 0.1	29 October 2012
Initial release with preliminary hardware.
Revision 1.0	18 November 2012
Updates for version 1.0 release. @@ -14,11 +14,9 @@ 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. -

Have fun using these products, and we hope to meet all of you out on the rocket flight line somewhere.

@@ -28,11 +26,10 @@ NAR Keith Packard, KD7SQG
NAR #88757, TRA #12200

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

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 -

+
- 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 @@ -58,17 +55,17 @@ NAR
- Finish preparing the rocket for flight. After the previous flight data have been reported, MicroPeak waits for - 30 seconds before starting to check for launch. This gives + 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 30 second window passes, + 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 30 second delay, but after + 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 10m in height - (32 feet), the micro-controller will record the ground + 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 @@ -80,7 +77,7 @@ NAR 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 @@ -110,12 +107,12 @@ 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. 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

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. @@ -124,19 +121,24 @@ NAR 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. + 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 @@ -145,7 +147,7 @@ NAR 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. @@ -188,11 +190,11 @@ NAR 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, @@ -222,7 +224,7 @@ NAR 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

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. @@ -236,7 +238,7 @@ NAR taken while the altimeter is at rest. Flight pressure is 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 @@ -247,8 +249,8 @@ 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, +

3. 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. @@ -264,7 +266,7 @@ NAR 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 @@ -280,7 +282,7 @@ 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 @@ -296,7 +298,7 @@ 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 @@ -309,7 +311,7 @@ NAR 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

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 @@ -329,7 +331,7 @@ NAR 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 × -- cgit v1.2.3