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Problem with counter as it only starts on earthing the ground

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avirajose

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hai,
As i told before, I'm doing a 4 digit digital stopwatch project. It consist of a 555 timer, four 4026 and 4 7-segment display. Everything works fine, but the counter starts the count only on earthing the ground.

Is it due to any grounding problem of my circuit or is there any other solution for it.
 

Re: problem in grounding

please post the schematic
 

Re: problem in grounding

I spotted 3 things, 2 of which are the possible cause.

Try connecting a 1k resistor from the counter reset input to ground, you have them just floating.

Also connect a 1 k from the first 4026 start/stop input to +v, again you have it just floating.

Floating inputs on these ic's will make them susceptable to noise on their inputs, grounding the whole circuit may well reduce this and make it work, at least for a while.

Also you have a 330r resistor and an unmarked device from the 555 pin 3 to ground, what purpose does this serve?, it'll probably work better without.
 

Re: problem in grounding

hai,
I designed my project on the breadboard. It works well. Away from the circuit diagram, i was forced to use 3 input and gate to detect 6. It works well on breadboard but as i designed the schematic on proteus the e,f,g pins of the 2nd 4026 does not goes high. But while removing the and gate it goes high.

Can any one explain it why? But it is not a major problem since it works on breadboard.

But my initial problem still exist. The counter does not start without earthing. I tried the previous treads but all was in vain.

 

Re: problem in grounding

The counter starts the count only on earthing. why it is so?
Is it due to any grounding problems
 

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