27 July 2016 User ReviewCheck your delivery options:
In this project, Resistive touch based keypad is used to control a device. Touch pad is kept in the bottom portion of the PCB. When power is given, Transistor T1 will be in off condition. One end of touch pad is connected to VCC and other end is connected to the base of the transistor. When your finger is placed in the touch pad, supply voltage reaches the base of transistor T1. Thus Transistor T1 will be turned on. Capacitor 100uf is connected between base of the transistor and ground to stabilize the voltage when finger is placed in touch pad. Once the transistor T1 is ON, 555 timer IC gets triggered and generates an output. Here timer IC works in monostable mode. The output of the timer act as the clock signal to D flip-flop.
In a D flip-flop, D input condition is copied to the output Q only when the clock input is active. Input pin of D flip-flop is connected to pin. Initially output of flip-flop (pin Q) will be low, hence will be high. As we place the finger on touch pad, 555 timer IC gets triggered and output from the timer is fed to D flip-flop as clock signal. Bit 1 at the input pin of D flip-flop will be copied to Q which turns on the relay. Device will be in ON state until the user touches the keypad for the next time. If the user keeps his finger again, device will turn off.
Fig 1:SK_004_v1 Circuit Diagram
Fig 2:SK_004_v1 PCB Bottom Fig 3:SK_004_v1 PCB Top
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