SMX: soil moisture Sensors transmitter

Figure 3: connection for current

Figure 3 shows how to connect the sensor for two wire current output. The black wire should be connected to the white wire. The output signal is a current that varies from 0.2 milliamp when the sensor is bone dry, up to over 1 milliamp when the sensor is soaking wet. The current on the two wire circuit may be converted to a voltage at the input of the data logger. A 1 k? resistor will convert the 0.2 to 1.0 millamp current into a 0.2  to 1 volt signal. The power supply voltage must be a high enough voltage to maintain the 4 volts required by the SMX module itself.

Figure 2: connection for voltage

Figure 2 shows how to connect the sensor for voltage output. The green wire is not used and should be connected to the white wire (not the black wire!). The output signal is a voltage that varies from <0.2 volts when the sensor is bone dry, up to over 1 volt when the sensor is soaking wet.

 Figure 1: connection for 50hz to 10,000 hz frequency output

Figure 1 shows how to connect the sensor for digital frequency output. The resistor (10kohms, value not critical) can pull up to any voltage from 3 to 7 volts dc. The output signal then is a square wave, and its frequency varies from 50 hz when the sensor is bone dry, up to 10000+ hertz when the sensor is soaking wet. This output can be measured using a COUNT or PERIOD function on the data logger. Note that the white and the black wires are connected together. 

Attach the Watermark sensor to the pair of blue wires. The polarity does not matter. (Please consult EME Systems if you are located in an area where there is lightning. The soil moisture sensor is intrinsically grounded at the point where it is buried. If there is a long cable between the sensor and your equipment, or if the equipment is itself connected to a different ground point, you must add a zap protection circuit to the SMX where it connects to the probe, and make careful consideration of the ground loop.)