Different types of soil moisture module

【Resistive style】
Most soil moisture modules in the market are resistive style. A resistive soil moisture module has two metal exposed probes, using the relationship between electrical resistance and water content to gauge the moisture levels of the soil. An electrical current is sent from one probe to the other to measure the soil's resistance between them. Due to water's good conductivity, the more water in the soil, the higher electrical conductivity is.
However, the resistive soil moisture module needs to be re-calibrated constantly (measured values are not stable) and have short lifetimes due to exposed metal components which oxidize and corrode easily in a moist environment.

【Capacitive type】
A capacitive type module uses only one probe to sense soil moisture through capacitance; the drier the soil, the lower the capacitance. Since a capacitive module does not have an exposed metal probe, it does not oxidize or corrode. This makes it suitable for agriculture and plant growth monitoring, as it does not pass DC current through the plants.

How to monitor the moisture value?

The BME34M101 features a built-in MCU, the BS45F3843, which measures soil moisture using the MCU's capacitive touch measurement system. The detection range is defined in percent (%) and ranges from 0% to 75%. In our practical test, when we watered the soil until it was completely saturated, the moisture level exceeded 60%. The more water in the soil, the higher the value. Users can easily determine the current moisture level by reading the percentage value.

Can cascade up to four BME34M101 modules

When you need to monitor the soil moisture of more than one potted plant, you can cascade up to four BME34M101 modules simultaneously, and only one of them needs to be connected to the development board.

To use with a development board

There is a BMCOM on the product to directly connect to BMduino development boards, such as BM53A367A. You can use it with other development boards, such as Arduino UNO, as well.