pH-meter connection



  • Hallo everybody,
    I've bought ph-meter PH-4502C and now want to connect it with Wemos D1 mini.
    There is analog output (as I understand Po). Powersupply for PH is 5V, with verification liquid it has on Po-pin 3,92V (more than 3V). So, but in Wemos specification is that on Analog input must be not more than 3v. How to make correct transformation? is it enough to use resistor and what value?
    0_1521369359717_HTB1KmFLaNHI8KJjy1zbq6yxdpXaU.jpg



  • @mouj

    It sucks, but there isn't much traffic on this board these days.

    The analog pin on the ESP8266 chip has a maximum input of only one volt. Look at the schematic diagram of the WeMos board you're using. For example, on the D1Mini schematic we see that WeMos feeds the input from the analog input pin (A0) into a voltage divider consisting of a 220K resistor and a 100K resistor. The analog input to the chip is taken at the junction of the two resistors so a 3.2V input will divide down to 1 volt at the chip's input (the maximum allowed).

    I'm no engineer, but I would think that if you added 180K of resistance to the D1 Mini's A0 pin, a full 5V would divide down to 1V, but I don't know if this is within the input impedance specs of the A/D converter.


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