Welcome to EnviroDIY, a community for do-it-yourself environmental science and monitoring. EnviroDIY is part of WikiWatershed, a web toolkit designed to help citizens, conservation practitioners, municipal decision-makers, researchers, educators, and students advance knowledge and stewardship of fresh water. New to EnviroDIY? Start here

Check out the EnviroDIY Mayfly Data Logger, a powerful user-programmable microprocessor board that is fully compatible with Arduino IDE software.

For sketches, libraries, and documentation, visit our EnviroDIY GitHub repository.

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  • Hello everybody,

    I am trying to measure conductivity from liquids water, water with salt, sugar, etc. I am using a conductivity switch sensor SEN0223 from DFROBOT brand. I would like to know first: Is this board suppose to work like an EC sensor? If yes, then I am having this problem:

    I always get the same conductivity readings on all the…[Read more]

  • Alright. I am getting the data right. Thank you for your help.

  • The way a voltage divider works is for you to use 2 resistors in series, and then you measure the junction between the two resistors, and you’ll see a fraction of the overall voltage. The best method for breaking a 5v signal down to something the Mayfly can tolerate would be to use two identical value resistors (like 10k-ohms each), so that way…[Read more]

  • Mark posted an update 4 days, 9 hours ago

    We will be using this temperature sensor

    • If you use a DS18B20 sensors, it requires a pullup resistor on the data line. You can connect the sensor data line to pin D10 and then just close the solder jumper SJ12 on the back of the Mayfly to enable the builti-in pullup resistor for that data pin. This saves you from having to add a separate resistor somewhere on the board to pullup D10.

  • Also, with the code you provided, if I do not use the voltage divider I can calibrate it to 2.5V if I remove the *2 from the equation. I am first time coder and also the mayfly is something new for me as well, I am learning little by little how this thing works. So the calibration will be right if I use the code without multiplying the 2?

  • Sorry for the late answer I had some stuff to do.
    Okay so, the circuit is connected like this:

    Voltage: V+ which is the 5V DC connected to SW5
    Ground: Ground to Ground
    Analog = PO or PH analog output is connected to the Analog pin A0
    I used three resistors to test which one will be close to the voltage required, I will post a picture of the three…[Read more]

  • Also, you need to use 3.3 volts as the board voltage in your conversion formula and not 5.0 volts. And if you’re measuring a 50/50 voltage divider, you’ll then need to double the measured voltage to get the true sensor voltage. So:

    float voltage = (sensorValue * (3.3 / 1023.0)) * 2.0;

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