Count-down timer

On this page, I will introduce the Count-down timer with PIC16F84A. I am putting a count-down timer by the hardware on Electronic Circuits Application Garage. The function of the timer is the same as it approximately. (The stop switch is added) Because this unit was made compactly, the wiring of the back becomes quite complicated.

This is PIC16F84A. In case of PIC16F84A, it is possible to use a clock frequency upto 20 MHz. The circuit this time, I am using 10-MHz resonator.

This is the IC which decodes the binary code of 3 bits. 8 conditions can be expressed by 3 bits. 74HC138 outputs only one an L level out of 8 by the 3-bit input condition.

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