Matt90

Hi. Sorry to be a pain :? I am doing a project on digital circuits for school, and would like to make a simple digital clock. I just don't really know where to start. I don't need anything fantastic, just somthing to help demonstrate how digital circuits are used in every day life. Thanks for any help getting me started!

Matt

stevez

Matt - as part of a "refresher" for myself I constructed a simple 1 kHz "square wave" generator from a 555 timer then took the output of that to a 7490 divider configured (wired) to divide by 10 - the output was 100 Hz - if I added two more 7490s, one right after the other I'd end up with 1 Hz and could drive a light. While this is not the digital clock it does rather clearly demonstrate some of the things that go on in a clock with a minimum of low cost parts. You might add yet another stage of divide by 10 to further demonstrate the digital division. All of the circuits were in various Radio Shack publications. I used a 5 volt supply to power everything. The 555 isn't critical but the 7490s want to see 5 volts. Jameco is one good source of parts.

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stevez

Matt90

Thanks for the idea stevez. But for me, this isn't really a refresher. I'm doing this for an 8th grade science fair project. So this stuff is new to me, but if you could try to explain that a bit more....if possible for someone with as little knowledge on the subject as me...I would appreciate that.

Thanks,
Matt

Johnson777717

Hey Matt90.
Please don't feel like you're being a pain for asking questions. We're all learning at our own different levels. Asking questions and helping others is the reason for this forum.

Here are a few digital clock circuits that I have found, hopefully these won't be too complex for your needs.
http://ourworld.compuserve.com/homep....htm#clock.gif (Look under 72 LED clock).

http://www.kmitl.ac.th/~kswichit/Led/Led.html
http://private.addcom.de/KeithWilson/Projects/caclo.htm
http://ourworld.compuserve.com/homep...wden/clock.htm
http://ourworld.compuserve.com/homep...den/dclock.htm

If building a clock is too complex, you may want to start with a display counter, or a binary counter etc.

Here's some good sites for finding circuits. I hope this helps!
http://ourworld.compuserve.com/homep...n/homepage.htm
http://www.discovercircuits.com/list.htm
http://www.commlinx.com.au/schematics.htm

stevez

Matt - if you are just beginning this just might be a good place to begin. I can't tell where in the world you live but if in US and you can get to Radio Shack I'd recommend their "Getting Started in Electronics" book. It won't have all that you need for this but it will come close. What it does have is some great hands-on stuff and non-technical explanations.

I found the 555 circuit, exactly what was in my RS book, on the internet and I'll see if I can find that (at home) and send it your way. It contains very few parts and it may be possible to reduce the frequency in order to limit the number of dividers that you'll need. Note that the whole point of the divider(s) is to slow things down so you can see what is going on.

Don't overlook kits as a solution. Vellman, among others, makes some nice kits. They do cost money but you are spared the struggle of obtaining parts, etc.

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stevez

Johnson777717

Good point Stevez:
I have a radio shack book called " Digital Logic Circuits" which of course, has a bunch of...you guessed it...digital logic circuits.

I'd be happy to draw a circuit or two up if you need Matt.

Matt90

Thanks for the help. I'll look into that stuff, and I'll be back with some questions I'm sure.

Matt

Matt90

I think I'll just try to do a basic counter/ timer........I would have to run a 555 into some kind of counter chip, then to the display :? right?

Could you please help me find the right shematic for this, and help me with what parts would be needed?

Thanks again,
Matt