Darren Harris wrote:
How many of these do you need? How big do the digits need to be? Is this
for production, or a hobby thing?


I need only one initially, but I'm sure other guys that I associate
with will also want one for themselves. But it's difficult to guess
how many in the end. That's why getting a list of all of the parts
needed so it can be duplicated is important.(Who knows. 50 guys may
each want one).

The digits need to be at lease 3 centimeters tall.

As for what I need it for. I am a competitive gamer on arcade video
games. And quite a few of us go for world records on various games and
platforms on a regular basis. It would be nice to be able to time
every level completed, as well as log the overall game time when
playing(for strategic as well as other reasons).

Thanks.

Darren Harris
Staten Island, New York.

Here is the display (common cathode):
http://www.digikey.com/scripts/DkSea...139499&Site=US

Using a 1MHz oscillator with a programmable divider chip like an
HEF4059B will yield an accurate 100Hz signal.

oscillator:
http://rocky.digikey.com/WebLib/CTS/...45HS,45HST.pdf

HEF4059B:
http://rocky.digikey.com/scripts/Pro...7&M=LDS-CA12RI

Using that signal to display a counter is easy. Here is a simplified
schematic:

http://home.comcast.net/~rcmonsen/stopwatch.gif

The strange OR gates are required to do leading 0 blanking. If you don't
care about that, omit the gates.

There is an on-off switch on the left, which gates the oscillator signal
into the counter logic. There are also two buttons, one which will reset
the counter to 0, and the other which will test the displays by turning
on all the segments.

You will need a power supply. A wall wart that puts out 8 volts or so,
along with a 7805 regulator and a couple of caps will do the trick. Look
up the 7805 on the National web site.

--
Regards,
Robert Monsen

"Your Highness, I have no need of this hypothesis."
- Pierre Laplace (1749-1827), to Napoleon,
on why his works on celestial mechanics make no mention of God.