From an old east-german numeric control, I salvaged a diplay with eight VQC10 display modules. Each showing four 7x5 dot-matrices. It was laying in my basement for several years. Now it was time to throw it away or make something usefull with it.


These modules are not so easy to drive. They have just for 5-bit latches for ervery dot in a row of a digit. The common anodes of all digits are connected together and need quite a high current. Every digit has it's own select-line so address decoding from five addressbits to 32 select-lines is needed.

The good news: this was done on the board I had. It has a 26-pin connector to drive it. East german type, narrower then normal ribbon-connectors...


Finding out the function of 26 pins was one saturday afternoons work, connecting it to an ATmega32 on a breadbord and writing a small program worked on sunday.

Then I read about the 7400 contest and tried it the hard way. Why use a single microcontroller when you can fill the breadbord with logic chips?

So I build this clock with 14 74HCxx chips and two eproms. The first eproms holds the texts to display. 32 characters for every minute of the day. There are 1440 minutes x32, that fits in 64 kByte. As the eprom I had laying around has 256 kByte, four different languges would fit in. Until now it can display german and english.

The second Eprom is the character-generator. Eight byte for every of the 256 characters would fit in an 2716, but the smallest I had was a 2764. So I could display four different fonts, but the one I use was hard enough to find...

The breadboard looks quite weird:


But well documented:


This is a not very exact diagramm of the old board:


The clock

The clock shows a different text every minute. The time can be set with two pushbuttons, one for minutes, one for hours.
Time can be displayed in up to four different languages.

A small video:

© 1999-2012 by Uwe Nagel, letzte Änderung am 13.04.2014