I want to link a PAR quantum sensor (either Licor or Skye Instruments) to Arduino to log PAR, in order to measure light in a forest. I have an Arduino Uno + data logging shield (with RTC, SD card and ADS1115) and have connected the PAR sensor via A0 to measure differential voltage (A0 –– S+ | S- –– GND | A1 –– GND). Code as follows:
ads.setGain(GAIN_TWOTHIRDS); adc0 = ads.readADC_Differential_0_1(); Voltage = (adc0 * 6.144)/pow(2, 15); Voltage = Voltage*1000; // conversion to millivolts
When I wire the Arduino to itself to measure a differential voltage (A0 –– 3V and A1 –– GND), it measures beautifully.
Furthermore, when I use a voltmeter to test the Voltage across the + - wires from the sensor, I get sensible readings.
Put the two together – nonsense. I get noisy V readings that don't make sense. When I cover the sensor my V is actually going up, not down as it should! I have tried changing the GAIN, but unfortunately this makes no difference to the problem.
I have been looking at PARduino for help/inspiration, but they include an amplifier in their setup, which is expensive and I'm not sure is necessary / would solve my problem.
Very new to Arduino. Any and all advice would be very much appreciated.