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Quantum Sensor

Home › Forums › Mayfly Data Logger › Quantum Sensor

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    • 2021-07-25 at 2:28 AM #15719
      Paulo
      Participant

        I am trying to use a Li-COR Quantum (LI-190R-BL) sensor to collect PAR data using a Mayfly cataloguer (v0.5b).

        I used a 620 ohm resistor to convert the sensor current out put to volts (0-5votls). Then, I connected the sensor to: A0 and GND, and tried to read the out put using this simple code, but I did not have luck.

        Any ideas?

        void setup() {
        Serial.begin(57600);
        }

        void loop()

        {
        float sensorValue = analogRead(A0);
        // Convert the analog reading (0-5Volts)
        float voltage = sensorValue * 63.3;
        Serial.println(voltage);
        }

      • 2021-07-25 at 7:31 PM #15720
        Shannon Hicks
        Moderator

          The Mayfly can only read analog signals from 0 volts to 3.3 volts, so you’re not going to be able to read something that puts out 5 volts.  But from what I can tell about that sensor from a brief look at the manual, it only outputs a maximum voltage of 10mv.  You’re supposed to use it with a separate amplifier if you want to be able to read it with a basic ADC like the Mayfly.  We typically use Apogee Instruments for quantum flux sensors because they have models with a 0v to 2.5v output range, which works perfectly with the Mayfly.  We also use the auxiliary ADS1115 ADC on the Mayfly for 16-bit resolution instead of the coarse 10-bit resolution of the built-in ADC of the ATmega1284.

        • 2021-07-25 at 7:56 PM #15722
          Paulo
          Participant

            Thanks so much for the info. However, if the sensor is not connected to an amplifier the max output should be around 200 mVolts.

             

             

            • 2021-07-26 at 12:20 PM #15723
              Shannon Hicks
              Moderator

                With such a small max signal of 200 mV, you’d definitely want to use the ADS1115.  The default ADC range has a resolution of 0.1875 mV/bit, which is pretty coarse so you’d want to use a higher gain setting like 8 or 16.  At gain 16, there’s a max input of 256 mV, and a resolution of 0.0078125 mV/bit.  Just be sure the ADC input doesn’t see anything more than 256 mV or you risk damaging the ADS1115.  Gain 8 might be safer and still has plenty of resolution.

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