One Hour Timer Circuit
This is a simple circuit of one hour timer device with an audible warning which can be operated using supply from a battery. This one hour timer circuit can be implemented as a parking meter timer.
How the circuit works:
This circuit works by using just two CMOS IC’s, a 4011 quad 2 input NAND gate, and a 4020 14-stage ripple binary counter. At switch on R2 and C2 give a brief reset pulse, that will make sure the output pin Q1 of the 4020 is high. Gates U1 and U2 form a simple astable R1 and C1 deciding the timing period. The tolerances of capacitors differ widely, so for extra control, you could possibly make use of a 470n capacitor for C1 and apply a fixed 3.3M resistor in series with a 250k preset for R1. A timing period of just lower than 1.76seconds is needed.
The output of the oscillator at U2 drives the input of the 14-stage ripple counter, U3. The outputs divide sequentially by two and the output signal is obtained from Q13, needing 2048 input pulses just before the signal is getting high.
Once the output Q13 goes high, the output sounder will come to be active. Gate U4 of the 4011 is utilized to “modulate” the output sounder. As U4 is also joined towards the output of U2, the output sounder will turn on and off at the same rate as the oscillator.
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