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 @@ -14,7 +14,14 @@ Add documentation for the MicroPeak USB adapter board. Note the switch to a Kalman filter for peak altitude determination. -

Acknowledgements

+ Revision 1.3.212 February 2014 + 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. +

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 @@ -26,7 +33,7 @@ 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

3.1. MicroPeak Graphs
3.2. MicroPeak Flight Statistics
3.3. Raw Data
3.4. Configuring the Graph

4. Setting MicroPeak Preferences

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 +42,7 @@ NAR open side of the carrier. Slip the carrier into the battery holder with the positive (+) terminal facing away from the circuit board. -
+
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 @@ -77,7 +84,7 @@ 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 @@ -107,12 +114,12 @@ 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

3.1. MicroPeak Graphs
3.2. MicroPeak Flight Statistics
3.3. Raw Data
3.4. Configuring the Graph

4. Setting MicroPeak Preferences

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. @@ -121,25 +128,27 @@ 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 - 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. +

2. Downloading Micro Peak data

+ Plug the MicroPeak USB adapter in to your computer.
+ Start the MicroPeak application. +
+ Click on the Download button at the top of the window. +
+ Select from the listed devices. There will probably be + only one. +
+ The application will now wait until it receives valid data + from the MicroPeak USB adapter. +
+ 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. +
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 @@ -147,7 +156,12 @@ 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

+ 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. +

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. @@ -166,23 +180,6 @@ NAR 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 @@ -190,7 +187,27 @@ 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

3.1. MicroPeak Graphs

+ 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. +

3.2. MicroPeak Flight Statistics

+ 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. +

3.3. Raw Data

+ A table consisting of the both the raw barometric pressure + data and values computed from that for each recorded time. +

3.4. Configuring the Graph

+ This selects which graph elements to show, and lets you + switch between metric and imperial units +

4. Setting MicroPeak Preferences

The MicroPeak application has a few user settings which are configured through the Preferences dialog, which can be accessed from the File menu. @@ -224,7 +241,7 @@ 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. @@ -235,10 +252,12 @@ NAR 60cm (24in) at 10000m (33000 feet).

Ground pressure is computed from an average of 16 samples, - 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

+ 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. +

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 @@ -249,7 +268,7 @@ 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 holds 30mAh of power, which is sufficient to run for over 40 hours. Because MicroPeak powers down on landing, run time includes only time @@ -266,23 +285,27 @@ 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 + 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 + 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. -

5. Mechanical Considerations

+ 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. +

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 @@ -298,7 +321,7 @@ 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 @@ -308,10 +331,11 @@ NAR

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 + 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. -

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 @@ -331,7 +355,7 @@ 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