Darren Harris wrote:
Splits = individual lap times.

I'll settle for a single LCD display if I have to.

Since this appears to be too complicated, perhaps I can start off with
something simple. Does anyone know how to build a simple timer with an
LCD screen that shows hours, minutes, and seconds?


Unfortunately, driving an LCD screen isn't a simple thing; they are
really designed to be driven using software. There may be front-end
chips which simplify them, but LED 7-Segment displays are much easier to
drive from discrete logic.

Building a 'simple' timer with discrete, digital logic isn't as easy as
it seems. You need

1) a timer source, like an oscillator circuit
2) a counter (or more like a set of counter chips)
3) logic to sample these counter outputs, and display the results on an
the LED segments.

At the least, this will require

1) a crystal oscillator/divider, like the philips hef4521b combination
oscillator/divider chip. Using a crystal, you can generate accurate one
second clock pulses

2) a set of bcd counters, one per decade of timing accuracy.
3) a set of LED 7-segment display drivers, one per digit.
4) some 7 segment displays
5) power supply
6) enclosure

You can get fancy and multiplex the LED displays, thus cutting down on
the number of chips required, but this increases the complexity a bit,
requiring more logic.

Note that a microcontroller costing less than a buck can replace 1-3
with a simple program of about 100 lines of assembler. Also, there are
designs for discrete timer circuits out on the web, if you want to look
and see what you are getting yourself into before starting.

If you decide to try to show speeds, you'll need division as well, which
is fairly easy in a microcontroller, and much harder with digital logic.


And that represents the simple version?

It seems that what I need is the same as what one of those racing
watches that record lap times do, but with LCD screen/s as a read-out.


Sorry, I was just trying to point out the complexities involved. If you
are just going to go out and buy a watch, and that works for you, fine.
I thought you wanted to build something.

Those watches you see are undoubtedly controlled by either a
microcontroller, or by a custom built chip of some kind, containing the
sorts of parts (on a miniature scale) that I described above. Almost
anything with any real complexity is done in software these days. Trying
to do this in discrete TTL logic, for example, requires up to 11 chips
for a 5 decade display.

You may be able to buy one of these watches, and hack into the buttons
to control it. However, the buttons are probably integrated into the
PCB, so it may take a bit of actual hacking. Doing a larger display
using one of these would be practically hopeless.

I'm sorry if this is not what you need, but you are asking for something
that isn't trivial. It may seem that it would HAVE to be trivial by
looking at the prices of these items these days. Those prices really
reflect mass production, and economies of scale, rather than simplicity.

--
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.