Technical Tips


Updated 22.12.15
Timer based on PIC16F628A LCD Module and a watch crystal. Included C code, and circuit diagram. Time span is 1 second to 99 minutes. Setting the time is by Min pushbutton which advances the minutes display by 2 per second, the Sec pushbutton advances the seconds. To reset the time press Sec and Min simultaneously.
The counting generated by the 32768Hz crystal oscillator.
The CPU frequency is 4MHz from the internal oscillator.
Egg Timer: CYCLE switch open. Pressing start turns on the LED and relay and starts the countdown. When the time reaches zero the buzzer sounds for 20 seconds. After the alarm the displayed time sets to the recent time.

Repeat Timer: CYCLE switch closed. Pressing start turns on the LED and relay and starts the countdown. At end of count down LED and relay toggle and count down repeats.

Older version of software included. You are free to use the circuit diagram and the software with no limitations.

Circuit Description
See also Technical Tips

LCD Module can be either 8 digits or 16X1 or 16X2
The buzzer is driven by a frequency of 2KHz, a piezo buzzer for that frequency will give optimal output.
The crystal is a watch crystal, refer to the data sheet for the recommended capacitors. Most crystals use 22pF-47pF.
The LED can be linked if not needed
Relay can be omitted if not needed.
The contrast pot can also blank out the display so set it if the display is dark or blank.
Pressing the Sec and Min together resets the time.