Introduction

This is another version of my "homebrew" or "Do It Yourself" altimeter and timer. I designed it to my own needs and preferences, but I think it will be useful or interesting (or maybe amusing?) to others. I've provided the schematics and printed circuit board design files, so that anyone can modify the design to their own preferences.

This is a work in progress

PC Board layout is complete and has been ordered.

Legal Stuff

Copyright 2008 Glen Overby.
The documentation, program, schematics, and printed circuit board design are free: you can redistribute it and/or modify them under the terms of the GNU General Public License, Version 2 as published by the Free Software Foundation.

THIS SOFTWARE AND CIRCUIT DIAGRAMS ARE PROVIDED BY AUTHOR AND CONTRIBUTORS ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL AUTHOR OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES.

... so don't get any grody ideas, ok?

Description

This altimeter is based on an Atmel AVR microcontroller with two sensors (a pressure sensor for acting as an altimeter and an accelerometer for acting as a timer or for staging at motor burn-out), a small serial EEPROM for storing flight data, and two high-current output transistors (P channel MOSFETs) for operating igniters or ejection charges. Both output channels have a continuity circuit, and the input voltage can be measured by the microcontroller via a voltage divider. An audible buzzer provides status to the user when the device is inside of a rocket. The software can be configured using two input buttons in combination with two LEDs.

Device

• Hardware Description
• Schematics
• Printed Circuit Boards
• Parts List
  Note: this parts list is of the parts that I had on-hand, and that I ordered from one place (Digi-Key). All of the parts could be purchased from Digi-Key, and most of the parts could be purchased from Mouser.
• Software
• Usage Notes

Previous Projects

This design I call "Alt7", as it's roughly my seventh altimeter design. This counts the pcboards I wrecked and the pcboard that had the wrong size footprint for the microcontroller.

YAFC

Yet Another Flight Computer Based on a Microchip 16F872, an MPX4101 pressure sensor, and an ADXL150. It recorded data to an I2C EEPROM. The software was written in PIC assembly and was abandoned because I got sick of writing assembly code!

Simple Altimeter (Alt4 current picture)

An early AVR based alitimeter. Peak altitude recording only.

I made two variations: one using a homemade circuit board, one using a board from PCB Express.

Alt5

I added output channels to the Alt4 design. Also has connectors for controling RC airplane servos. I was experimenting with mechanical (spring and elastic) deployment mechanisms when I designed this.

I've flown several successful flights with this altimeter.

Alt6

Another AVR based altimeter, this time the ATmega168. Like my earlier YAFC, this has both a pressure sensor and an accelerometer and records to I2C EEPROM. This data helped me debug my "dumb apogee detection" algorithm.

Glen Overby
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