9-0 seven segment counter

Thread Starter

Sparky49

Joined Jul 16, 2011
833
Hi everyone.

I'm looking into seven segment displays, and I think I've got a reasonable idea of how they work.

However, I cannot seem to find anything which allows a countdown. Clearly this is possible, and I probably missing something obvious, but can someone point me in the right direction?

Nothing complicated, something like 9-0 would be great, without PICs that is.;)

Thank you very much for your time, I really appreciate it. :)

Sparky
 

Thread Starter

Sparky49

Joined Jul 16, 2011
833
That's spot on crutschow! Thanks.:)

Just to confirm some things:

http://www.jameco.com/Jameco/Products/ProdDS/676502-DS01.pdf

1. As I'm counting from 9 to 0, can I just leave pin 9 floating or shall I tie it to ground?

2. For pin 7, should I use a monostable input to avoid 'bounce'? If so, what would be a good time period?

3. If I'm not needing to reset, can I leave pin 5 floating?

4. What does latch enable do?

5. I need to use borrow. How does this connect within the circuit? Also, what should I do with carry?


Thanks for taking a look, I think I just need a bit more confidence and re-assurance that I'm doing things correctly.:)

Sparky
 

Thread Starter

Sparky49

Joined Jul 16, 2011
833
I've had a go at the connections.

How does this look?

I will add resistors for the display later, but are the other connections correct?

Thankyou.:)

Sparky
 

Attachments

crutschow

Joined Mar 14, 2008
34,285
If you look at the schematic of the chip you will see that borrow and carry are outputs so you want to leave them open, not tied to Vcc or ground as you show.

For your purposes you can just tie the Latch Enable to ground although connecting it to the clock will work also. If the Latch Enable is high then the display value is held constant, independent of any change of the counter value.

You need a one-short or other type of debounce circuit if the clock is coming from a mechanical switch. The period should be at least 100ms.
 

Thread Starter

Sparky49

Joined Jul 16, 2011
833
Thanks again Crutschow.:)

I will complete the schematic tomorrow. Would you mind giving it a quick check again?

Sparky

P.S. Wally is my favourite character too!
 

Thread Starter

Sparky49

Joined Jul 16, 2011
833
Phew, the hardest part was stretching the canvas for paint. It took me longer than drawing the circuit!

Does this look reasonable? I think the values of components are correct, but I'm not 100% sure.

Sparky
 

Attachments

Top