Generating a 1 Hz clock?

Thread Starter

BlackCow

Joined May 11, 2009
65
I was interested in making a digital clock out of 74* series chips. The only thing I am stuck on is generating a precise clock cycle. I'm assuming a 555 is no where near accurate enough.

I was thinking about using a crystal, but I have no clue how to make one work, or how to divide one down to 1 Hz.

Could someone point me in the right direction? I don't mind ordering another type of crystal but the ones I do have on hand are 8 MHz and 4 MHz.

Update: If anyone stumbles upon this thread I did eventually build this clock using a quartz clock circuit as the time base. Thanks for the advice jgessling!
 
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MikeML

Joined Oct 2, 2009
5,444
Hack a $4.95 battery-powered wall-clock. The hands are moved by a two-coil stepping motor. Each winding is pulsed at 2Hz, starting from a 32Khz crystal. Stability is within a few seconds per year...
 

jgessling

Joined Jul 31, 2009
82
I've been running my TTL clock on the breadboard for a few days now and I'm very pleased. I used a crystal from an old battery powered clock as seen on this site. http://www.josepino.com/?one_second_timebase
Look down to the modification schematics. Mine is like the one with the transistor except instead of a LED I used two diodes in series to give 1.4v across the crystal. Since the battery would give 1.5v maximum I thought it best to stay below that. Not sure that's a big deal though, try it out. Keeps real good time too. Search this site for previous discussions of this topic.
 

retched

Joined Dec 5, 2009
5,208
Woah. You would need some serious division. Its possible, but over kill. Have you read the josepino link? It works great. I get the clocks from the dollar store, for a dollar.;)
 

BillB3857

Joined Feb 28, 2009
2,570
If you are going to be using a wal-wart for power, use an AC 'wart. Divide the line freq by 60 and you have super accuracy.
 

Thread Starter

BlackCow

Joined May 11, 2009
65
I think I'm going to go with the cheap dollar store clock hack haha. Thanks for your help guys.

Edit: Good news, I found an old micky mouse battery operated clock, perhaps I can incorporate micky into my design XD
 
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jgessling

Joined Jul 31, 2009
82
I did have trouble at first with the junk clock circuit. An LED would flash fine but the pulse wouldn't clock my chips right. Put the output from the crystal into a 7414 (schmitt trigger inverter) and the output of that worked fine. Hope this helps.
 

Thread Starter

BlackCow

Joined May 11, 2009
65
I've been running my TTL clock on the breadboard for a few days now and I'm very pleased. I used a crystal from an old battery powered clock as seen on this site. http://www.josepino.com/?one_second_timebase
So I tried using the circuit on that site, when I ran the two half hertz cycles through diodes I couldn't get a pulse out the other end, but when I took the two clock lines, tied them together into my decade counter it worked fine! Each line was about 2.3 volts so I guess added together they are pretty much a TTL 5 volts.

Thanks for your help guys!
 

jgessling

Joined Jul 31, 2009
82
Looks just about the same as mine, thanks. Can I ask you what you used to draw that schematic? I'm looking for just a simple drawing tool, I've used several things for simulation: ltspice and hades they were very good and I tried Eaglecad (too small limitation) and ExpressPCB (too limited parts) for drawing and both are pretty hard to learn. I am now just looking for something to draw my schematic so I can save it before going to the soldering stage. This is my first real project and so I am worried that I will lose the design when I make this transition from the breadboard.
 
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