Simple humidity detector

  
The main (and only) job of this circuit is to activate a buzzer or a relay, each time the level of humidity takes a specific value. Main stage is a memory based on a flip-flop consisting of gates and IC1a IC1 b. The output of this step activates an oscillator (IC1c), which in turn leads to a piezoelectric speaker. At the start of operation of the circuit, the flip-flop is driven to logical '0' or through the C1 or through C2. From the moment you excited, the reintroduction of the peace achieved through the switch S1, which however is insufficient if the sensor 82 continues to be wet.
Simple humidity detector - schematic

The piezoelectric speaker can easily be replaced by a ilektronomo which in turn activates another external power device, such as a horn, a lamp or anything else is able to provide a distinctive indication. For the relay should note that because the current that drives the coil is pulsed (DC = 50%), the voltage should be less dp 'is the voltage of the detector. If for example supply voltage of the latter is 9 n, then the relay is good to work at 6 V. The current circuit absorbs the rest of the order of 4-5 mA, but increased to 40 mA if the tow relay contacts. The supply voltage can be between 3 and 15 n, but if you use the lower limit relay is limited to 8 V. If during the use of the circuit proved highly sensitive, you can reduce. the value of R2.




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