FAQ automation

The SMT50 has an output resistance of 10 kOhm. Most controllers have a much larger internal resistance at their analog voltage input, so that the measured voltage corresponds to the output voltage of the SMT50. In the Loxone controller, however, the input resistance is only 10 kOhm. Therefore a voltage divider is formed and the Loxone controller displays only half the voltage value. As a remedy, one simply multiplies the measured voltage with the factor 2 in the Loxone software and can then use the calibration characteristic curve in the data sheet of the SMT50 again.

The simplest connection to the Loxone control succeeds with the SMT100 analog 0 - 10 V. However, the disadvantage is that you need a separate analog input for each sensor. If you want to measure the temperature in addition to the humidity, you need 2 analog inputs. If there are several sensors, a bus system is more suitable. From Loxone there is a so called Modbus Extension, to which up to 32 sensors can be connected. For this you need the SMT100 RS-485 Modbus version.

AN002: SMT100 Modbus Quickstart Guide

AN005: SMT100 ASCII Text Command Guide

AN003: SDI-12 Quickstart Guide

There are a variety of options for irrigation control with soil moisture sensors:

Controls from the field of building automation, e.g. Loxone or KNX

Controls from the general automation technology (e.g. PLC from various manufacturers)

Professional irrigation controllers with standard interfaces like 0 - 10 V voltage input

DIY solutions based on Arduino or with other microcontrollers

Raspberry Pi based systems (e.g. OpenSprinkler)

Radio based systems e.g. with the radio standard LoRa

The choice depends on both the requirements and the budget.