Model Rocket Altimeter
The goal of this project was to create a user-programmable altimeter for use in model rocket competitions, such as the Team America Rocketry Challenge.
The altimeter has a ATmega168 running Arduino. Everything is powered by a 9-volt battery going through a 7805 voltage regulator, which then supplies 5 volts to the electronics.
For data recording, the ATmega168 doesn’t have enough EEPROM memory for long term data logging. So for this project I chose a 128k (16 kilobyte) I2C EEPROM from Microchip.
The actual device that measures the altitude is a Freescale barometric pressure sensor, a MPX4115A. It outputs an analog voltage that the ATmega168 reads.
The user interface consists of a LED and a pushbutton.
There is a lot of room for improvement – here’s a short list of what will be done for future revisions. First, the 7805 regulator is very wasteful, and the 9-volt battery is large and heavy. A better solution would be a low-dropout or switching regulator, along with a lithium-polymer battery. The barometric pressure sensor is designed for huge pressure ranges – so in the ranges of most model rockets, the sensor is not very accurate. A better solution would be to put the analog output into a series of op-amps to isolate the voltage range that I need. The external EEPROM will be replaced with a MicroSD card which has much greater storage capability. Finally, the user interface will be upgraded with an external handheld LCD display.