altimeter

This altimeter is designed to work with Team Black Sheep's Crossfire and Tracer PWM receivers, and should also work great with any RC receivers that are able to speak Mavlink telemetry at 15200baud, and transmitters that can receive and display it. Note that this altimeter does not work smoothly as a variometer. If you want vertical speed data also, check out the Octopilot Alt/Vario sensor instead.

It uses an MPL115A1 barometer, and converts pressure to altitude. Since pressure changes quite a bit with the weather, its is recommended to zero-out the altitude value on your transmitter on every launch, and then view the relative altitude during the flight.

It sends Mavlink messages to your transmitter that are meant to include GPS lat, long, and altitude, but just sends zeroes for lat and long, along with the real altitude data.

Altimeter Setup: To connect to your RC receiver, solder a short servo cable (or pin headers for a direct connection into your radio receiver) to the 3 pads on the altimeter. The square pad is Ground(-), then VCC(+3V to +5V), then Data. (See photo for pin-out.) Then make sure to cover the barometer chip such that air can circulate into the tiny hole, but light can not get in. Light leaking into the barometer can throw off the altitude data by tens of meters!

Radio Setup: Then set up your receiver's Output Map to set up the appropriate channels (3 & 4 for my nano RX) as Mavlink RX and Mavlink TX. Connect the altimeter to the Mavlink RX channel's pins, since the receiver will be receiving Mavlink data from the altimeter. The Mavlink TX pins are unused, so I use those pins to connect my battery. Make sure your RC TX has Telemetry set to On. Then power up your plane and transmitter, and tell your transmitter to Discover New Sensor. It should find a few new sensors, and the one you want to use is ALT.

Then use this value as you want! I set up my Discus Launch Glider to speak my altitude 3 seconds after each launch, to get instant feedback on how high my launches are going.

Board specs, without wiring or tape/heat shrink:
Size: 11mm x 16mm
Weight: 0.8g

Note that this product is unrelated to the UDB5mini/UDB6mini, and is meant for gliders/planes without a full flight controller.