A “two hour weekend project”.

My friend bought 51-based clock kit a time ago. But he wants a kitchen timer.

So I look around and identify: YSZ-4 kit with 4 position LED display, powered by Atmel 89C2051.

Here is a schematics:


Here is display datasheet, the most important thing is “colon” is DP for position 2.

I used SDCC compiler and MCU 8051 IDE. This IDE has embedded emulator for some hardware, e.g. multiplexed display 😉


(“Ahoj” means Hello in Czech.) I used online calculator to determine timer constant.

Kitchen timer is controlled by two buttons, SET and RESET. SET sets desired time in minutes (00-99, I know, it’s crazy, but useful when you want to measue a hour and half or so). RESET cancells counting or alarm.


It was really simple, two hours of work, including experiments.

Here is my source code. Feel free to use.