Unsure why this demultiplexed digital counter isn't working

[BlueMythic]

Same project, different problem - we need to create a 4-digit counter using a 74139 demultiplexer (attached file).

We got the demultiplexer to output the right clock signals now (I think), and in a wonderful breakthrough, the seven-segment displays are displaying something! The problem: They're displaying blinking zeroes, when they're supposed to be counting upward.

(Other problem: we need to use a Schmitt trigger as our clock source, which is that floating bundle above the four probes - but first we want to get the rest of the circuit working, so we're using the generic digital clock sources for now).

I think the problem is with how we've wired either the 7447 BCD decoders, or the 7473 JK flip-flops (or both). We got a working counter circuit with a different design, but we were reminded that the circuit has to integrate a 74139 demultiplexer, and trying to get that to work has left us at another roadblock. Anyone have any hints on where the problem is on this circuit?

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EDIT: Some more experimenting (and the discovery of digital probes) has showed us that the problem is likely either in the JK flip-flops or the demultiplexer output. Attached the slightly-updated file - no wiring changes really, just some better-placed probes.

[andmboa7]

do you know the logic this JK flip-flops use to work? The displayed numbers are only 0 and randomly displayed.

What does this JK needs to work properly? Is it going to pass values on high?

-Andrea Gamboa

National Instruments

[BlueMythic]

Sorry - looks like there's been another change to our circuit and this design isn't the exact one we're using anymore. On the plus side, someone in the group did figure out what the problem was - we had the flip-flops wired incorrectly for what we're trying to get them to do (output BCD binary).

Turns out, we needed to include some additional logic gates, which we weren't using because of a misunderstanding (the instructor gave us data sheets of some of the specific parts we have access to, but we failed to realize that of course he would also have various basic logic gate packs, and just because he didn't give us a data sheet for a component didn't mean we couldn't use it).

I don't have the file on this computer or I'd attach it to show what I mean, but the long and short of it is: We figured out that the problem was a lack of necessary logic gates on the flip-flops that would allow them to output BCD.

[andmboa7]

Excellent!

Good to know!

Good luck!!

-Andrea G

National Instruments