The SMT100 is a premium soil moisture sensor from Truebner with excellent accuracy for demanding applications in science and precision agriculture. Researchers and farmers have trusted the sensor for over 10 years. It combines the advantages of a low-cost FDR sensor with the accuracy of a TDR measurement.
Operation with OpenSprinkler
The SMT100 is available in two versions for OpenSprinkler:
- RS485 Modbus (recommended): Requires this RS485 adapter for OpenSprinkler (€59). Up to 4 sensors on one adapter. Digital, highly accurate transmission.
- Analogue 0..3V: Requires this Analog sensor board (€59). Simple cabling, no additional adapter required.
Technical data
| Characteristic | Value |
|---|---|
| Measuring principle | High frequency FDR/TDR hybrid |
| Accuracy soil moisture | ±3% VW (factory calibration), ±1% VW (soil specific) |
| Accuracy temperature | typically ±0.2°C, max. ±0.4°C (analog version: ±0.8°C) |
| Soil moisture resolution | 0.1% VW |
| Resolution temperature | 0.01°C (analog version: 0.2°C) |
| Soil moisture measuring range | 0–60% VW (up to 100% with limited accuracy) |
| Measuring range temperature | -40 to +80°C (analog version: -40 to +60°C) |
| Interfaces | RS-485 (TBUS/Modbus/ASCII), SDI-12, Analog 0-10V, Low Voltage UART |
| Power supply | 4-24V DC, 40mA max |
| Measuring time | < 50 ms (digital), < 500 ms (analog) |
| Cable length | 10 m |
| Dimensions | 18.2cm × 3cm × 1.2cm |
Documents & Downloads
📄 Datasheet SMT100
📄 Instructions SMT100
📄 AN001: SDI-12 with Campbell Scientific
📄 AN002: Modbus Quickstart Guide
📄 AN003: SDI-12 Quickstart Guide
📄 AN005: ASCII Text Command Guide
📄 AN006: 4-20 mA tutorial
📄 AN007: Low voltage UART
Sensor comparison: SMT100 vs. SMT50
| Characteristic | SMT100 | SMT50 |
|---|---|---|
| Measuring principle | FDR/TDR hybrid | FDR |
| Accuracy soil moisture | ±3% / ±1%* | ±3% typ. |
| Accuracy temperature | ±0.2°C | ±0.8°C |
| resolution | 0.1% VW | 0.2% VW |
| Measuring range temperature | -40–+80°C | -20–+85°C |
| Interfaces | RS-485, SDI-12, Analog, UART | Analogue 0-3V |
| length | 18.2cm | 13.5cm |
| For OpenSprinklers | RS485 adapter or Analog board requires OpenSprinklerShop firmware |
Analog sensor board |
* Soil specific calibration
We recommend the for simple garden watering and home users SMT50 as a cheap alternative.









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