PIC16F877 Based Timer Circuit

The project was built around a PIC16F877 microcontroller along with a single 7-segment LED display and a piezo speaker at its output for the timer circuit.

What comprises the inputs are the two pushbuttons for setting and starting/stopping, two bits of 8-position DIP switch for timer selection, and a 10-position BCD rotary switch for digit entry. Two breadboards were used wherein one contains the PIC16F877 microcontroller and most of the components of the timer while the other contains the serial port adapter circuit used for programming and the DIP switch.

There are four independent count-up and count-down timers and the current value of user-selected timer is displayed. A separate I/O pin of the PIC is connected to each of the attached devices for protection and regulation. This also applies to the piezo buzzer to protect the PIC. The switches are connected to +5V with pull-down resistors to ground while the speaker is connected directly to an output pin. the speaker is connected in series with a resistor to limit the worst case current below the maximum since a piezo element behaves like a capacitor. The display is continuously refreshed by the program’s main loop.

Rest of the project