Simple and practical human approach detector circuit diagram

  
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Human approach detector circuit is composed of integrated operational amplifier, gate circuit and resistor-capacitor unit in the diagram. Among them, 1MHz oscillator consists of reverser T1, 1MHz crystal oscillator and resistor-capacitor unit. The oscillator signal is shaped by T2 and then T2 outputs square signal. It adopts a piece of 25cm2 copper clad plates to make up inductor.
Simple and practical human approach detector circuit diagram - schematic

Human body is equal to another polar plate when human nears the copper clad plate. It can generate capacitance enlarge along with human`s approach and the capacity is 2~6pF. This incremental capacitance can make the after IC3 output pulse signal which pulse duty factor is proportional to incremental capacitance. One way of T2 outputted square wave is sent to comparer IC1B by R3, and is add to one input end of XOR gate IC3 after enlarged; another way is first delayed by R1 and C1, than enlarged by comparer IC1A and added to another input end of XOR gate IC3, thereby the duty factor of XOR gate IC3 outputted square signal is in direct proportion to the delay of R1 in the input circuit, then it generates DC current which is in direct proportion to the distance of human approach after filtered by R6 and C4.



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