Input devices

Capacitive soil moisture with ESP32

Look at the chip before you trust this sensor. Good boards use a TLC555 or similar CMOS timer, which works at 3.3 V. Some cheap clones have an NE555, rated down to only 4.5 V, and they behave unpredictably at 3.3 V. If your readings jump around, that small marking may be the reason. Resistive probes corrode quickly; capacitive ones hold up better, which is why they cost a little more.

The output runs backwards: dry soil gives a higher voltage, wet soil a lower one. Forgetting that is the most common bug. There is no true percentage either. Read the sensor in air and in a glass of water, and scale between those two values. Results change with soil type, compaction and supply voltage, and two sensors from the same bag can differ. Recalibrate if you change any of them.

Water kills these boards from the top. Push it in only up to the marked line, since the timer chip and edges above that have no protection. One builder saw readings go wrong after about six months in wet soil, and coating the exposed electronics is a common fix. Powering the sensor from a GPIO only while reading is suggested too, and on a battery it saves energy. On an ESP32 use an ADC1 pin if WiFi is on. LCD Ultra Pro can read an analog pin in a rule and scale it to a range, so a bar can show moisture without code: enter a reversed minimum and maximum, based on your own readings.

const int AOUT_PIN = 4;
const int DRY = 2800, WET = 1200;     // replace with your own readings

void setup() {
  Serial.begin(115200);
}

void loop() {
  int raw = analogRead(AOUT_PIN);
  int pct = constrain(map(raw, DRY, WET, 0, 100), 0, 100);
  Serial.printf("raw %d  moisture %d %%\n", raw, pct);
  delay(2000);
}

Use this information at your own risk. It is for general guidance only: the example code compiles, but it has not been tested on every part, and modules differ between sellers. Check the manufacturer's data before you build. Product names belong to their owners, and LCD Ultra Pro is not affiliated with them. See our Terms.