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seperating digits on two 7-segments

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abuarab88

New Member
hello everyone,

i have a project that do the following
we have akeypad and two 7-segments
we need to dispaly anumber from 00 to 99
the problem is when we press 9
it gives 99
if we press 7 it gives 77
how can we seperate each number alone on the 7-segment
you can see my circuit in the attachments

we are forbidden of using pic microcontroller
 

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ericgibbs

Well-Known Member
Most Helpful Member
hi,
When using the 74C922 'DA' you have a 'race' condition between the inverted signal driving the 4027 clock and the two AND gate outputs driving the 'LE' on the 4511's.

You need to add a delay circuit in the DA lines/4027/AND.

Use a scope and you will see the 'timing' problem and the point where the delay is required. OK.?:)
 

abuarab88

New Member
hi,
When using the 74C922 'DA' you have a 'race' condition between the inverted signal driving the 4027 clock and the two AND gate outputs driving the 'LE' on the 4511's.

You need to add a delay circuit in the DA lines/4027/AND.

Use a scope and you will see the 'timing' problem and the point where the delay is required. OK.?:)

thank you
but i really did not understand your answer
if you have simpler circuit but that one i put
i would be glad
thanx
 

crutschow

Well-Known Member
Most Helpful Member
I believe the circuit logic is incorrect. The 4511 requires a "1" on the LE input to latch the data. With no keypad input both LE inputs are "0" (DA=0)which means they both respond to the BCD input signals. You need to invert the LE signals to the 4511's inputs. That way the LE signal selected by the FF will go low when the BCD output is valid (DA=1) and the BCD data will be input. This will then be latched into the 4511 when the keypad button is released (DA goes low) and LE goes high.

Also the 4511 /BL and /LT lines must be connected to logic high for proper operation.
 
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