If you were or are an electronics geek, I have a fun problem

[jmowreader]

I am attempting to build a device which contains three or four digital clocks, all with LCD readouts--a Varitronix 153-1103 display would be just fine.

Clock 1 is just a plain old 24-hour clock, nothing too spectacular. Having an alarm function on it wouldn't be bad.

Clock 2 and 3 would be tied together. These would be more like stopwatches. Clock 2 will run continuously once activated, and it should have an alarm. Clock 3 will be able to be started and stopped without stopping clock 2, and it will also have an alarm.

Clock 4, if I use it, will be another stopwatch. It will run independently of clocks 2 and 3.

Now for the question: should I try to buy regular clock chips like we used back in the 1970s to do this with, or should I use 7490 and 7492 counters?

[midnight armadillo]

1. None of the above.

Now for the question: should I try to buy regular clock chips like we used back in the 1970s to do this with, or should I use 7490 and 7492 counters?

Get a PIC and do it all in assembler. Or C (my pref since I don't do assembler enough to retain it in RAM) - there are free compilers available. I think a programming board w/ a USB connection to your PC will set you back maybe $40 and it should come with maybe 2 PICs of varying capabilities.

[jmowreader]

2. How much outboard gear do I need to get a PIC to talk to 3-4 displays?

And, more critically, do PICs multitask?

Being able to maintain three or four completely disparate clocks is critical to this operation--this isn't like one of those clocks that shows four time zones. One clock might say 14:43, another 2:25 and a third 5:15. And the one that says 2:25 might start and stop twenty times in one day, whereas the one that says 5:15 will continue running until it's reset and the one that says 14:43 won't ever reset; it will just flip over at midnight. I'm afraid that if I do everything in software, eventually I'll wind up needing a used PC laptop so I can multitask. (I'm trying to be deliberately vague on what this is because as of right now, this product doesn't exist in the form I envision and it's something a lot of people need.) As for the fourth clock...it just needs to count off ten hours and turn on a light. That's easy in hardware--two 74LS90s, a 74LS92, some LCD driver chips and a J/K flip-flop to hold the light high once the clock rolls over past 9:59.

Now let's get REALLY fun: What I would really like to happen is the two or three timers to count down, not up.

[midnight armadillo]

3. hmmm...

...I'd have to say "not sure" as to how much extra outboard hardware you'd need. Most of my PIC experience has been applications that do things like "flip pin 1 high after reading A->D converter for 10 seconds" which basically all happens in software. I don't see any reason why you couldn't write a loop to run all four clocks while watching a hardware clock for ticks - you might vary by a few milliseconds here and there.

Man, I do too much Labview these days, I sort of miss messing around with real low-level hardware. One thing to keep in mind (and I'm sure you know this) if you have a commercial application in mind is parts count which effects labor needed per board etc. This is where a microcontroller could be handy.

[csziggy]

4. My $3 kitchen timer does 1-3 of your list.

You can probably find an kitchen timer that will do all four.

Why do you need to make your own?