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Looking for comments on my thoughts.

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Blapto

New Member
End result will be a 4 digit counter that increments every time input goes high.
What I need in my mind is a units BCD counter, a tens BCD counter, a hundreds BCD counter and a thousands BCD counter. I then need a multiplexer system that sends that information to a BCD decoder/drive for a 7 segment display, then 4 x 7 segment displays hooked up to another multiplexer.
First question, will this actually do what I want it to do? As a contrast to other posters, I would rather you didn't post completed circuits, I want to discover this for myself, however I would appreciate it if you shot my idea down in flames because of some gaping hole.
Thank you in advance.
 

Blapto

New Member
Right, I have been thinking. I need to use 4510s for my 1, 10, 100, 1000 counters, and a series of logic gates to sense when the output changes from 0110 to 0000.
I seem to be using this as my notepad.

Edit:
Nope, I am an idiot again, I want to use the carry out. Isn't that a take away :p

Edit:
Bad news, I have been thinking again. Mental logic goes something like, surely it would be nice if I could build this as a clock instead? So, I began to think about the multiplexing again. I need to communicate with 6 x 7segs now (23:59:59), and I have only seen 2, 4 and 8 to 1 multiplexers. Could I just connect the final two poles to the first two outputs, as it should still be fast enough?

Edit:
Right, I don't want to create superfluous posts, so in here it goes:
Can I use a 555 as my clock source? Use it astable with Tmark as 0.1s and Tspace as 0.9s. Is it reliable?
 

ljcox

Well-Known Member
Have you considered the 4533? It is a 3 digit BCD counter, I think (I don't have a data sheet) that it has internal mulitplexing.

As for the multiplexing, you could use the 4052 Dual 4 channel analogue multiplexers as these can be wire "ORed".

Another possibility would be to use Tri State devices. I don't know if there is a Decade counter with Tri State outputs. If not, you could use Tri State buffers. The point is that Tri State outputs can be wire "ORed".

As for designing a clock, there have been other posts recently from people designing clocks. You may find some usefil ideas in these posts.

I don't know what you mean by "Could I just connect the final two poles to the first two outputs, as it should still be fast enough?"

Len
 

J0HN1

New Member
Hi Blapto,

Its not a good idea to use an R-C time constant as a reference
for timekeeping.
You would really need a crystal controlled frequency.
The higher frequencies are a little better timekeepers, but even
low frequency crystal control oscillators are ok for clocks.

The thing with clocks is that any error is cumulative,
so even a slight error will build up fairly quickly.
R-C timing is slightly affected by many factors, temperature,
humidity, even barometric pressure could have an effect.

The simplest thing for a regular one second pulse that i have
ever found is the unit from an old quartz clock. They can
usually be found easily. Its usually the plastic parts that fail,
the electronics is usually fine. They are very accurate and use
very little current. A excellent starting point for a divider.

Best of luck with it, John :)
 

Blapto

New Member
ljcox said:
As for the multiplexing, you could use the 4052 Dual 4 channel analogue multiplexers as these can be wire "ORed".

Another possibility would be to use Tri State devices. I don't know if there is a Decade counter with Tri State outputs. If not, you could use Tri State buffers. The point is that Tri State outputs can be wire "ORed".

I don't know what you mean by "Could I just connect the final two poles to the first two outputs, as it should still be fast enough?"

Len
First, what does "ORed" mean?
Second, I have outputs switching between 1, 2, 3, 4, 5, 6, 7, 8, if I connect outputs 7 and 8 to ground, it will effectively wait for two switches in between 6 and 1. Is that effective?
 

Blapto

New Member
Sorry guys, but I am totally confused about the multiplexing issue. Current thinking is I need 6 inputs (s, 10s, m, 10m, h, 10h) each with 4 inputs (the binary takes 4 bits) to be diverted to the same on the other end (6 outputs each with 4 outputs) and then to use another multiplexor to ground the correct 7seg in time with the rest of the circuit. Am I in the least bit correct?
 

ljcox

Well-Known Member
Len[/quote]
First, what does "ORed" mean?
Second, I have outputs switching between 1, 2, 3, 4, 5, 6, 7, 8, if I connect outputs 7 and 8 to ground, it will effectively wait for two switches in between 6 and 1. Is that effective?[/quote]

I should have used the term "wired OR". This is an OR gate created by wiring. I'll post a diagram with my next post (in answer to your next post)

I don't understand your second point. A diagram would help.

Len
 

ljcox

Well-Known Member
Blapto said:
Sorry guys, but I am totally confused about the multiplexing issue. Current thinking is I need 6 inputs (s, 10s, m, 10m, h, 10h) each with 4 inputs (the binary takes 4 bits) to be diverted to the same on the other end (6 outputs each with 4 outputs) and then to use another multiplexor to ground the correct 7seg in time with the rest of the circuit. Am I in the least bit correct?

Yes, this is correct. The attachment is the promised "Wired OR" explanation.

You may be able to also find an explanation on the internet

Len
 

Attachments

  • Wired_OR_104.gif
    Wired_OR_104.gif
    6.9 KB · Views: 936

ljcox

Well-Known Member
Blapto said:
OK, is the correct IC required a 4 pole 4 throw 8-to-1 multiplexer?

Four (ie. one for each bit) 8-to-1 multiplexers will do the job, with 2 inputs not used (remember to connect the unused inputs to gnd).

You will also need a Demux (such as the 74HC42) to drive the display cathodes

Len
 
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