ESP8266 Community Forum

- Tue May 03, 2016 6:48 am #46764 I need to make a voltage divider for a soil moisture sensor as seen on the attached image, for use with an ESP-12.

Since the ADC on the ESP requires a range from 0-1V I have used a 2.7K and 1K resistor to get it from 3.3V to ~0.9V. However, it seems like the sensor is short circuited (maybe), when I attach ground to the 1K resistor - see images below. When ground on the right side (black cable) is attached to the 1K resistor, the led on the sensor is turned on and the output measured from the voltage divider (white cable) is basically 0V.

I also tried with 27K and 10K resistors. I also measured the output from the sensor before attaching the voltage divider, and it outputs realistic values e.g. when putting the sensor into water.

Did I attach something wrong or can I not do it with a simple voltage divider?

Soil moisture sensor with A0, D0, GND and VCC


Ground attached to voltage divider on the right side. LED on sensor is turned on. 2.7K and 1K resistors (also tried 27K and 10K)


Ground removed from voltage resistor, LED turned off on sensor

Robot enthusiast | Indie developer | Enjoys life

- Wed May 04, 2016 7:42 am #46861 Remember that the sensor acts as resistor itself; perhaps the 1K resistor has a value too low, compared to the value of the sensor, and is basically acting as a pull-down. I would try to make the divider using resistors with larger values.

- Wed May 25, 2016 4:54 pm #48016 Work for me on a similar sensor with 100k and 47k resistors.