Capacitive Soil Moisture Sensor v1.2
Capacitive soil moisture sensor that won't corrode — ideal for long-term plant watering projects.
Unlike resistive probes, this capacitive sensor doesn't corrode over time, making it the preferred choice for long-running automated plant watering builds. The sensor works by measuring the change in capacitance between two exposed copper plates embedded in the probe as soil moisture content changes, entirely without running any current directly through the soil (unlike older resistive probes) — since there's no direct electrical contact current flowing through the wet medium, the sensor doesn't suffer the electrolytic corrosion that eventually kills resistive soil probes.
Specifications
| Sensor type | Capacitive soil moisture probe (v1.2), corrosion-resistant compared to resistive-type probes |
| Operating voltage | 3.3V–5.5V DC |
| Operating current | ~5 mA typical |
| Output | Analog voltage, inversely related to moisture — drier soil gives a higher voltage, wetter soil gives a lower voltage (or vice versa, check your specific board's convention) |
| Interface | Single analog output pin, read with analogRead() |
| Durability | No exposed metal contacts in direct current-carrying contact with soil, significantly longer usable lifespan than resistive probes |
| Calibration | Requires per-sensor calibration (a 'dry air' and 'water' reading) since raw analog values vary between individual sensors and soil types |
Pinout
| Pin | Name | Description |
|---|---|---|
| 1 | VCC | Power, 3.3–5.5V DC |
| 2 | GND | Ground |
| 3 | AOUT | Analog output — read with analogRead(), inversely proportional to soil moisture |
Take a reading in dry air and a reading fully submerged in water to establish the sensor's practical analog range, then map subsequent readings between those two calibration points to get a 0-100% moisture-ish scale — raw analog values are not standardized across different soil types or even between individual sensor units, so skipping this calibration step will give inconsistent results in different soil.
Variants
Always prefer the capacitive sensor over an older resistive probe for any project that will run for more than a few days, since the resistive design corrodes and fails relatively quickly with regular exposure to wet soil. Consider an I2C capacitive variant only if you'd rather skip manual analog calibration in exchange for a higher price.
| Variant | Temp range | Hum range | Accuracy | Protocol | Price |
|---|---|---|---|---|---|
| Capacitive soil moisture sensor v1.2 | ~$2-4 | ||||
| Resistive soil moisture sensor | ~$0.50-1.50 | ||||
| Capacitive soil sensor with I2C output (e.g. Chirp/I2C variants) | ~$8-15 |