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Digital Clock

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Hello all,

I have to produce a functional digital clock using 7 segment displays. Can someone explain how a digital clock works and also point me in the right direction.

All i have right now is a 74283 connected to a 4511 to display it on a 7 segment display.

I really dont understand how to make this work. Ive been looking at a bunch of schematics and im just getting even more confused.

Thanks,
Tiago
 
Are you any good with microprocessors? This is an ideal project for a PIC microcontroller. If you are going to progress your electronics career, I strongly suggest you have a play with them - they will really make your expertese much better. I would avoid using discrete logic blocks.

You also need to look at Real Time Clocks (RTCs). these cute little chips have a 32Khz oscillator connected to them and increment seconds, days, months, years, day of week etc and take a whole ton of grief away from clock designing.

As for the 7 segment display, take a look at the MAX7219. this drives 7 segment displays.

But you really need to start with a micro at the heart of the design and you can learn PICs in a matter of days - and there is a whole ton of software on the net to get your started!
 
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Are you any good with microprocessors? This is an ideal project for a PIC microcontroller. If you are going to progress your electronics career, I strongly suggest you have a play with them - they will really make your expertese much better. I would avoid using discrete logic blocks.

You also need to look at Real Time Clocks (RTCs). these cute little chips have a 32Khz oscillator connected to them and increment seconds, days, months, years, day of week etc and take a whole ton of grief away from clock designing.

As for the 7 segment display, take a look at the MAX7219. this drives 7 segment displays.

But you really need to start with a micro at the heart of the design and you can learn PICs in a matter of days - and there is a whole ton of software on the net to get your started!

I cant use a microcontroller.

Ive worked on it a bit more and i think i got the "seconds" portion down but i need to create a 60hz signal to connect to pin 14 on the first 7490 correct?

How can i do this? I read using a 555 timer is inaccurate and that i should produce it using a crystal? How do i go about doing this?

I attached the part for the seconds. Is that correct?
 

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You need an accurate 1 Hz signal. A 555 is not accurate enough. There are 3 obvious frequency references that are accurate enough.

50 or 60 Hz mains. The mains signal can be transformed to a safe voltage and then divided by 50 or 60 to give 1 Hz
32768 Hz watch crystal. You need a simple oscillator circuit followed by a divide of 32768. There are lots of ICs that will divide by that.
A higher frequency crystal. Again, a simple crystal oscillator, followed by a suitable divide. That may take more ICs.
 
You need an accurate 1 Hz signal. A 555 is not accurate enough. There are 3 obvious frequency references that are accurate enough.

50 or 60 Hz mains. The mains signal can be transformed to a safe voltage and then divided by 50 or 60 to give 1 Hz
32768 Hz watch crystal. You need a simple oscillator circuit followed by a divide of 32768. There are lots of ICs that will divide by that.
A higher frequency crystal. Again, a simple crystal oscillator, followed by a suitable divide. That may take more ICs.

Can you give me a diagram please? Also im simulating this in multi sims. Does it have crystals in its database?

I also have to make this run off a 9v battery. I have to reduce it down using a 7805 though correct?

Your circuit to divide by 60 looks OK. Do you want the displays connected to the 7447s in your diagram to show minutes or seconds?

I have the displays connected i just couldn't fit it in the screen shot. The 7 segment displays are connected to the corresponding pins on the 7447's. I have to run a 220ohm resistor in between each though correct?
 
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Okay...

To make a simple digital clock, I would firstly choose a nice good stable clock source. this is just a square wave that has a frequency of 60Hz. You could use a 555 timer but it would need to be fine tuned with a potentiometer. I would suggest using a pierce oscillator which allows you to use standard crystals to genetate a square wave clock signal (Pierce oscillator - Wikipedia, the free encyclopedia).

Now that you have this 60Hz signal just use a bunch of counters
i.e.
Clock Signal -> Seconds Counter -> Min Counter -> Hour Counter.

The seconds/min/hour counter will all comprise of 2 counters each.

You could then use some gate logic to link seconds to min and mins to hours. i.e when the first digit of the seconds is a 6 then reset and clock min

Hope im making sense.
 
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