Ads1115 - A0 input voltage reading when nothing hooked up

I am testing ADS115 boards and have a weird issue.

When I connect one to an esp32 using DuPont cables. The A0 measure voltage is always 0.5-0.6V, even with nothing connected to the A0 pin. I have tested with 3 different ADS boards and 2 different esp32’s with the same result.

I have 1 ads board that works as expected, A0 shows 0.00xxV when nothing is connected and it works reading a CT clamp sensor.

Are the ADS boards bad? Or am I missing something?

wiring

Esp32 ↔ ADS1115

  • SDA ↔ SDA
  • SCL ↔ SCL
  • 3.3V ↔ VDD
  • GND ↔ GND
  • None ↔ A0 disconnected: multiplexer set to A0_GND

Try offset filter

Input impedance of this chip is in the range of Mohms. Did you try with inputs floating? If so, inputs will show noise.
Try to add pulldown resistor, can be quite big, 10 kohm, 100kohm or similar…anything but floating. For testing purposes you can connect A0 directly to GND and see if it reads zero.

After grounding A0 with a 68k resistor, the channel reads as it should.

Thanks!

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