Simple Moisture Detector(CD4093)

This article describes the Simple Moisture Detector (CD4093). The principle is very simple, very practical. The circuit components can help you understand better grasp this principle. For example, in this circuit, you can go to find and buy these components: CD4093.

The function of this circuit is to sound a buzzer, or, optionally, actuate a relay, when a certain moisture level is detected between a pair of probes. The circuit has a ‘memory’ in the form of a flip-flop, IC1a-IC1b, which enables or disables a tone oscillator, IC1c. The flip-flop is reset either by C1 and C2 when the supply voltage appears, or by push-button S1. This may not reset the alarm, however, which will sound again until the probes are ‘dry’. The (passive) buzzer may be replaced by a relay actuating an externally connected sounder, lamp or other high-power signalling device. Because the duty factor of the coil voltage is about 0.5, the relay should be a type with a coil voltage which is lower than the supply voltage.

Circuit diagram:

Figure 1 Simple Moisture Detector Circuit Diagram

A 6-volt type is suggested if the circuit is powered from a 9-volt supply. The circuit has a modest standby current consumption of between 4 and 5 mA. This rises to about 40 mA when the relay is actuated. The supply voltage is uncritical and may be anything between 3 V and 15 V. Note, however, that it may not be possible to use a relay if a supply voltage lower than about 8 V is employed. If the circuit is found to be too sensitive, the value of resistor R2 may be decreased.

 

 

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