Solar Radiation

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This topic contains 5 replies, has 2 voices, and was last updated by  Shannon Hicks 2 months, 2 weeks ago.

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  • #2265

    TheoJass
    Participant

    I am looking to use a Mayfly with a solar radiation sensor. It’s a simple, 3-wire analog sensor and I think it’s standard in weather station equipment. Does anyone have experience doing this, or a sketch to share?

  • #2267

    Shannon Hicks
    Keymaster

    I have used several solar radiation sensors with my Mayfly boards, so it’s possible, however it really depends on what the excitation voltage of the sensor is, and what the analog signal’s output voltage is. Can you tell me the make and model of the sensor, or at least what are the power requirements and output voltage?

  • #2269

    TheoJass
    Participant

    Thanks for the response. We’re using an Apogee SP-110, which is self-powered (doesn’t draw from the battery) and provides output in the range of 0-250 mV. The 3 wires go to a positive and negative signal from the sensor and a ground.

  • #2271

    Shannon Hicks
    Keymaster

    The Apogee SP-110 will work fine with the Mayfly. Just connect the signal wires to AA0 and AA1 (the aux analog inputs) and do a differential measurement. You’ll need to use the Adafruit_ADS1x15 library and look at the example for differential measurements.

    We always use the amplified output versions of Apogee’s solar sensors instead of the self-powered ones because they have much better sensitivity. There’s an order of magnitude improvement in the sensitivity by using the amplified ones, and it results in a much cleaner signal too. The SP-212 is the amplified (2.5v) equivalent of the SP-110, so I would recommend that instead if you haven’t already purchased the sensor.

  • #2272

    TheoJass
    Participant

    Thanks again. We’ll probably stick with the SP-110 since we have a few already in the lab. I found in a datalogger manual that they recommend using it as a single-ended analog sensor, where the positive wire is the signal and the negative wire is an additional ground. I saw in the ADS1x15 library that there is a folder for singleended. Would I just follow that example and keep the wiring the same? Or would I wire both “ground” wires to the ground pin (black wire on the starter kit)?

  • #2273

    Shannon Hicks
    Keymaster

    Sure, if the manual says it’s okay to ground the sensor’s negative signal wire, then you can just connect the sensor’s ground and negative signal wires to a “GROUND” pin on the Mayfly, and then connect the sensor’s positive signal wire to one of the Mayfly’s auxiliary analog pins. The easiest way to do this is with one of these Grove-to-screw-terminal boards:

    https://www.robotmesh.com/grove-screw-terminal

    If you’re using aux analog pin 0, then the following code will work for reading your SP-110 sensor. I put the correct conversion factor in the sketch for your particular sensor. If anyone tries to use this sketch with other sensors with different conversion factors, they will need to change that part of the sketch.

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