8 June 15

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We created the thermistor circuit on June 4 and wrote the code to read it.  It it composed of a 1,000 ohm (1kohm) resistor connected to a 1.8V rail, in series with the thermistor connected to the ground rail. Voltage is measured by the beagle between the resistor and the thermistor, telling us the voltage drop across the thermistor. Using this, the value of the known 1K resistor, and the supply voltage of 1.8V we can calculate this instantaneous resistance of the thermistor using the formula:
R = 1K / ((1/ADC) - 1)
(Formula modified from Adafruit note: same page a last post linked to)

 Using the resistance and the formula listed in our previous post, we were able to calculate the temperature that the thermistor should be sensing. Note: Since our thermistor has a negative temperature coefficient (listed in the datasheet) we expected to see the resistance of the thermistor decreases as the temperature increases, which is in fact exactly what happened experimentally. Our code can be found at https://github.com/bccBalloon/HiBalloon. We also soldered the thermistor and the 1K resistor in series to our board, after adding a 1.8V rail and extending the ground rail on the underside of the protoboard.


We will work on attaching the ribbon cable to the circuit board and also work on calibrating the accelerometer. We will also be working on getting values from the magnetometer (the red board in the above picture) which is an HMC5883L (datasheet here) on a breakout board from sparkfun.
SparkFun Triple Axis Magnetometer Breakout - HMC5883L
SparkFun Triple Axis Magnetometer Breakout - HMC5883L
(Source)

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