1

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.

Improve this question
3
  • 1
    Could you connect the sensor to the Arduino and, at the same time, to the voltmeter? Do you still get sensible readings from the voltmeter if you do so?
    – Edgar Bonet
    Commented Dec 10, 2019 at 8:24
  • Please provide a link to the datasheet of the used sensor. I'm not sure, if you can simply omit the amplifier
    – chrisl
    Commented Dec 10, 2019 at 8:51
  • Thanks for your comments Edgar and chris. The problem must have been arising from a faulty board or some such. In the end, I was able to wire up the sensor as described above, using a more fleshed-out version of the code. No amplifier necessary, you can just adjust the GAIN. I then ran my Arduino sensor alongside a Skye Instruments SpectroSense 2+ to 'calibrate' it. Plotting the Arduino voltages against the SpectroSense PAR values gave quite a nice fit! Apologies for the long delay in replying – was on fieldwork.
    – sinderJ
    Commented May 12, 2020 at 4:18

0

Reset to default

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.