Saturday, February 19, 2011

GAGA-1: Working flight computer

And so after much preparation and the early success in getting RTTY transmission working I soldered everything onto the custom Arduino shield that forms the flight computer, plugged it in and... it just worked!

Here's the flight computer board connected to the Arduino. The biggest item is the Radiometrix NTX2 module with a small voltage divider below it which is used to set the frequencies for the 0 and 1 values. The antenna is connected to the SMA connector bottom left.

Just above the radio is the DS1821 temperature sensor that will measure internal capsule temperature. It has an associated pull up resistor. The external temperature sensor connects to the three pin header to the right of the radio (it too has a pull up resistor).

Here's a log of transmitted temperature data received via RTTY:
$$GAGA,24.0,Error: 0,$$GAGA,24.0,Error: 0,
$$GAGA,24.0,Error: 0,$$GAGA,24.0,Error: 0,
$$GAGA,24.0,Error: 0,$$GAGA,23.9,Error: 0,
$$GAGA,23.9,Error::C'fwyZ '/A,23.7,Error: 0,$$GAGA,23.7,Error: 0,
$$GAGA,23.7,Error: 0x$$GAGA,23.8,23.3,
$$GAGA,23.7,22.9,$$GAGA,23.7,22.6,
$$GAGA,23.7,22.6,$$GAGA,23.7,29.8,
$$GAGA,23.7,29.7,$$GAGA,23.7,27.6,
$$GAGA,23.7,26.1,$$GAGA,23.7,25.0,
The first few lines of reports show the internal temperature (24.0C---yes, it's warm in the basement) and an error report (Error: 0) for the external temperature. The error was happening because I didn't have the sensor plugged in. I recently enhanced the code that handles the DS1821 sensor to report errors. Error 0 means that the sensor didn't respond.

The garbled output is because I was fiddling around with my radio. I then plugged the sensor in it started reading temperatures. The temperature peaked at 29.8C because I held the sensor in my hand.

Next steps are: a long distance test of transmission to make sure that's working correctly and install the GPS. With the GPS I'll be at the end of the long GAGA-1 road.

PS One final shot of the Arduino shield showing the painful leg bending required to fit in with the Arduino's silly pin spacing.

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If you enjoyed this blog post, you might enjoy my travel book for people interested in science and technology: The Geek Atlas. Signed copies of The Geek Atlas are available.

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