PIC CLOCK - MATRIX DISPLAY

Ever since we moved to our home (in late 2003) we couldn't have a permanent wall clock in the living room. We tried putting several clocks but they stopped after running several weeks even though the clock and the battery is good. Some of them are still working in other places. So we didn’t try to put any more. After I build two small scale clocks, I wanted to build a bigger one for the living room. Here are some pictures of the clock. Still it is too early to say that the same thing will happen to this as well.

The display is created using a LED matrix. This is because I couldn’t find a suitable size seven segments in the market. Display comprises of four 4x7 matrices with a colon and a decimal point which is driven by two MAX7221. RTC is DS1307 with DS32KHz crystal. Temperature sensor is DS18S20. The brain of the clock is gigantic 40 pin PIC16F877A with 8k code space. Everything is assembled inside a plastic box file. Working with the two display drivers (MAX7221) was not that difficult but they didn’t work without the two 0.1uF capacitors close by. Program was slightly modified to accommodate two display drivers with the new numeric font. I designed several fonts and finally settled with the one shown.