I'm very new to this. I found this tutorial.

But it don't explain how to read voltages higher than Arduino 5V. I have connected a 100K ohm resistor to positive and 10K ohm to negative of my 24V power supply.

I need some guidance for writing the code for this specific ADC, please.

  • So you want to measure the voltage of your power supply?
    – chrisl
    Commented Oct 14, 2019 at 14:05
  • Yes i want to measure voltages higher than 5V.
    – BIGsmall
    Commented Oct 14, 2019 at 14:57
  • You cannot measure much more than 5V with that device neither. (VDD +0.3V) You and that "tutorial") use an adafruit library and should get information from them. If those 2 resistors (100k + 10k) build a voltage divider and negative is connected to GND, 24V is reduced to 24V/11 ~ 2.18V between the two resistors. Commented Oct 14, 2019 at 15:01
  • i know that Datafiddler but i don't know how can i convert and read that 2,18V to 24V!
    – BIGsmall
    Commented Oct 14, 2019 at 15:03
  • It's called "math". For example: Arduino has 10 bit precision and usually 5V reference voltage. That means one step is 5V / 1024 = 0.004883V. And if you divide input voltage by 11, that means you have to multiply previous result by 11 too.
    – KIIV
    Commented Oct 14, 2019 at 15:11

1 Answer 1


As KIIV mentioned you need to do the math:

Use this online voltage divider calculator to calculate your maximum input.

  • Keep in mind you shouldn't exceed Arduino 5V.
  • Use a multimeter to measure the resistors actual resistance.
  • Do the math for your example assuming R1 is exactly 100K and R2 10K you have to multiple the voltage by 11.
  • remember any error is going to multiple by 11 too, so make sure the first reading is accurate/stable.

ADS1115 is actually 15bit which will give you resolution of 32768, with default PGA setting you get: 6.144 / 32768 = 0.0001875V per bit.

Voltage = (your ADC reading) * 0.0001875V;
Voltage = Voltage * 11;

Take a look at This question/answer to see how I did reduced Arduino ADC noise, some steps can be done for ADS1115 as well.

Your Answer

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

Not the answer you're looking for? Browse other questions tagged or ask your own question.