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4 DIGITS LED EGG TIMER

Count down timer based on PIC16F628A and a watch crystal. Included C code and circuit diagram. Time span is 100 minutes. Setting the time is by MINUTES / SECONDS pushbuttons which advances the minutes display by 1 per second. Holding the pushbutton counts faster. Pressing MINUTES and SECONDS together resets the display.
Pressing START / STOP starts the countdown. Pressing START / STOP during count pauses or restarts the counting. When the time reaches zero the buzzer sounds for 10 seconds and the display flashes.
 

2 DIGITS LED EGG TIMER

Timer based on PIC16F628A and a watch crystal. Included ASM, C code, and circuit diagram. Time span is 1 to 99 minutes. Setting the time is by +MINUTE/RESET pushbutton which advances the minutes display by 1 per second, the +MINUTE X 10 pushbutton advances the tens of minutes digit. Pressing START sounds the buzzer for 0.25 sec and starts the countdown. When the time reaches zero the buzzer sounds for 20 seconds and the display flashes 'AL'. Pressing +MINUTE/RESET pushbutton resets the timer and/or stops the buzzer.

You are free to use the circuit diagram and the software with no limitations.

Circuit Description
See also Technical Tips

Transistors are BC337 or equivalent.
The oscillator is a watch crystal of 32.768 KHz. The 22pF can vary with different crystal makes.
The 4 digits display is common cathode, the 7 resistors of 220 ohms enable current of 16 mA max averages at 4 mA through each segment which is on for quarter time. The seven segments, a to g, of one digit are linked to the corresponding seven segments in the other digits.
The decimal point can be used between minutes and seconds. Alternatively you can use different colour or smaller size digits for the seconds display.
The buzzer,  piezo buzzer is driven by a frequency of 2KHz.

 

 

Circuit Description
See also Technical Tips

Transistors are BC337 or equivalent.
The 2 digits display is common cathode, the 7 resistors of 390 ohms enable current of 6 mA total averages at 3 mA through each segment which is on for half the time. The seven segments, a to g, of one digit are linked to the corresponding seven segments in the other digit.
The 2 digits are multiplexed by pins 17 and 18 that drive the common cathodes.
The buzzer is driven by a frequency of 1KHz, a piezo buzzer for that frequency will give optimal output.

PCB for 2 Digits Timer by GAB GOB
Gabriel designed a PCB for this project using EAGLE PCB 5.9 .