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Archive for April, 2013
Posted by grmis | Apr 17, 2013 @ 04:10 PM | 29,793 Views
Let me share this cheap and simple barometric altimeter. It is largely based on this altimeter (by KapteinKuk), except that it uses a cheaper BMP085 sensor, and the altitude is sent to the ground via an FrSky telemetry link. It also sends the time from start, the current temperature and the max. temperature. All these data appear on a FLD-02 telemetry screen for instance. A lot of informations concerning the FrSky serial telemetry protocol (including links to several arduino codes) can be found on this thread.
And here is another similar project: OpenXVario.

To get a reasonable accuracy, the arduino code makes the average of 10 consecutive measurements and sends the results every 300ms. The accuracy seems to be of the order of 1~2m. This can be made more accurate by taking more, say 30, measurements and sending the result once every second (conversion time is about 30ms).

Here is the code:
#include <LiquidCrystal.h>

// Author: Grmis, 04/2013
// Arduino Pro Mini 3.3v connected to BMP085 barometer breackout
// throught I2C
// Arduino connected to 'RX' line of FrSky D8R-2 receiver
// through digital Pin (use SoftSerial with inversion)
// Although the arduino is 3.3v, it seems that the 5v receiver understands it :-)

// code based on the original codes by:
// Rolf R Bakke
// R.Schlohan
// BMP085 Extended Example Code by: Jim Lindblom (SparkFun Electronics)

#include <Wire.h> // I2C to communiucate with the sensor
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