Digital Clock Circuit Modification Question

Hello all. I am fairly new to the world of digital electronics, and to get me started, I am building a digital clock out of CMOS 4000 series logic ICs. The schematic for the clock can be seen at the following URL:

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Now, that clock uses 24 hour time, I want there to be a switch that will let me enable 12 hour time. By using some other gates, I have come up with an addon to the circuit. It can be seen here:
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When the the first digit of the hour is "1" (0001) and the second at "3" (0011), the quad input AND (made of 3 dual-input ANDs) is triggered and it resets both and sets the hour's second digit to a "1" by pulsing the "CLK" pin.

Will this work, though? I have my doubts.

-Zach

Reply to
Zach Zaborny
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Hi, Zach. I'm not sure what's going on with the second link - it seems to be broken or missing. You're describing the right concept on a 12/24 switch, though. If you get together another 3-input AND gate (requiring another IC, I'm afraid) and switch between the AND output on the schematic and the one you're proposing, you should be spot on. All you really need are the three 1s

- you don't have to add any 0s to the decoding for the alternate reset signal.

A couple of points. First, using the 555 to generate a 1.000 Hz timing signal is weak. You'll get drift, mostly from changes in capacitance with temp. If you're in for a penny, you're in for a pound. If you're going to go to all the trouble of doing this much counter logic with 4000-series CMOS, add another divide-by-50 or divide-by-60 counter to get 1.000 Hz from your power supply transformer. It may drift slightly from hour to hour, but our friends at the power station are kind enough to bump the power frequency during the night to keep the daily total remarkably steady at 5,184,000 cycles per day (60 Hz).

The second thing is, this circuit has been basically a wire wrap or perfboard wiring exercise for at least a decade. It would be a lot easier with a PIC.

Good luck Chris

Reply to
CFoley1064

Okay, at first I had no idea how to use the mains line for a clock, but this circuit has helped, it is for a binary output clock:

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One problem though: his site is not based in USA, but rather in Europe. The power in hi area oscillates at 50hz, while mine at 60hz. I used his modification for 60hz and edited his design a bit for it:
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It looks like it will work. Except, can I use a CMOS 4000 series dual-input AND for the oscillator instead of the 74LS08? I plan to run mine all on 9V, so it would be more appropriate.

As for the 12/24 switch, I didn't notice my mistake :). But, will it reset the hours to "01"? As the AND triggers, it outputs a pulse to the RESET and CLK pins on the 4510 for 2nd-digit hours, as seen here:

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As for it being easier on the PIC; I think that's cheating. I would rather play with discrete logic circuits and parts than have one microcontroller do all the work :) I do understand it's ease of use being handy though. Call me old fashioned.

-Zach

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Reply to
Zach Zaborny

you might want to check

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, under the header 'Getting started with it: the proper timing' you can find another CMOS-based way of generating 1Hz. It uses a crystal and is therefor independent of the frequency of the mains line. (The circuit works, I've build it from this site and my clock is running on time for a few months now.)

bye, Olaf

Reply to
Olaf

Thanks, I'll probably use that for it's simplicty and ease of us :). The Nixie clocks are very nice, and may be my next project, since it looks very interesting.

Thanks once again, Zach

Reply to
Zach Zaborny

if you're interested in nixie's: you can find a lot of homebrewn nixieclocks at

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and at
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you can see some pictures of my nixieclock (just ignore the Dutch). I've used Peter Wendt's circuit for this clock. At
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there are some pictures of the big 7segment display's I'm using for my current clock-project. I still needed a (non-pic-oriented) circuit for that, so the link from your original post was most welcome ;-)

bye, olaf

Reply to
Olaf

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