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Operation of 3-minutes Digital Counter

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Wjs

New Member
Hi,

When I simulation this only one display working.

What goes wrong or the gate i used wrong.

Please advise.
 

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mvs sarma

Well-Known Member
please download and see the function table of 74LS247 and the note 3 below the tables. People believe that unused pin is High, but need not always be.

Hence the condition needed sappers to be RBO pin to be pulled UP . You might use 1K resistor for that.
 

mvs sarma

Well-Known Member
Fine Ian Rogers,
for some reason the OP did get only 1 digit.
i suggested him to add pull up on 74LS247 "rbo' pin.
the truth table shows like that and He need not leave them open, i suppose.
 

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Wjs

New Member
I tried but still same only one display is counting another two display not counting. are the gate issues ?
 

mvs sarma

Well-Known Member
Can you perform Lamp Test(LT) checking how to do from the datasheet for the respective digits that refused to glow?

possibilities are that displays either faulty or model changed , unless the number tallies. you could sawap the LS247 chips one by one to the working display to check their performance.
Later restore to original locations and try swapping the display devices.
I assuem that you are working on Breadboard.
 

mvs sarma

Well-Known Member
i see
once it works on breadboard, forget it
the simulators might have their own deficiencies.
all the best
 

JoeJester

Active Member
When you breadboarded it, did it count past 59 without advancing the minute digit to 1 the first time you fired it up?

If you built it like you drew it, it will.
 
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