Circuit Lake

SmartProbe is simple low cost moisture and temperature alarm system for plants. Insert it in the plant’s root system and it measures the moisture and temperature. It sounds an alarm if the moisture or temperature goes out of preset limits. Shut it off with a gentle tap or knock on it to ask it the current status. Temperature, moisture and battery status is indicated by tone sequences. It won’t disturb your sleep at night for it monitors light. It also warns you when the battery is getting low.

This R8C/13-based device is useful to gardening enthusiasts who often forget to water their plants or are prone to over-watering. Plant growers in regions experiencing extreme low or high temperatures may rely on the temperature alarms to reduce the risk of plant loss through frost.

The project uses 4 sensors: vibration, temperature, light, and moisture. The vibration sensor is equivalent to a switch and interfaces directly to the INT0 interrupt of the R5F2113. With the vibration sensor sealed in stainless steel, it makes a good replacement for (and is cheaper than) waterproof switches. The temperature sensor is a NTC thermistor. Its resistance is measured using the A/D converter.

The light sensor is a Light Dependent Resistor (LDR) connected to the A/D converter. The moisture sensor is based on the properties of a gypsum block. Gypsum block as part of an R/C timing network is used to measure soil tension. Soil tension is related to soil moisture content. The resistance of the gypsum block is measured indirectly by measuring the frequency of the timing network that it is part of.

Smart Probe
Project Firmware, Schematic and Documentation
circuitcellar.com