pic: Custom Built Stopwatch

[Kyle Fenton]

Originally Posted by D.J. Fluck

Thats pretty cool, what kind of chips did you use and how long did that take you?

The main counting feature is done by the Motorola 4553, which is counter that counts up to 10 (0-9). It was a pain to figure out how to use, but once we got it working it was pretty straightforward.
The cool thing about this is that it doesn't use any flip-flops, we can make the 4553 do the counting from 0 to 9 and then 0-5. Basically this how it works, the first counter is the least significant number or in this case milliseconds, it is run off a 555 timer that goes into a 4520 counter. However we use the 4520 as the clock signal, and not the counter. The clock signal come out of the 4520 goes into the clock signal of the first 4553 which 0-9 milliseconds, when that count reaches 10 we use combinational logic to detect it (using AND Gates and inverters) to send a send a signal to reset it self, and also to send a signal to other counter in line to count. This logic can be directly applied to all the other digits. For our project we only went up to 60 minutes .

If you want to learn more about this, I have a whole PowerPoint presentation I can send you.