I need a circuit that has two inputs A and B. If A detects positive edge then regardless of what the B input is,
the output will be a high level of 5 volts.

On the otherhand, If B detects a positive edge then regardless of what the A input is, the output will be a
low level of 0 volts.

thanks

 

Is this homework?

 

What is the output when both inputs are Low?
Are these positive edges a brief pulse?
Looks like a Set- Reset.

 

Use two monostable multivibrators controlling an S-R flip-flop.

 

I need a circuit that has two inputs A and B. If A detects positive edge then regardless of what the B input is,
the output will be a high level of 5 volts.

On the otherhand, If B detects a positive edge then regardless of what the A input is, the output will be a
low level of 0 volts.

thanks

"regardless of what the B input is" includes the B input also having a positive edge. Similarly for the other input.

So you have a contradiction in your requirements.

You need to resolve that.

 

Use one of the EDGE TRIGGERED devices, either a CD4027 fliflop with the "J" high for the rising edge trigger and the "K" high for the falling edge trigger. That will sense the edges. But now the question is what will the output be until there is an edge????

 

What happens if the positive edges of A and B occur simultaneously?

 

Probably that is prevented from happening by whatever condition is causing the pulses.

 

Probably that is prevented from happening by whatever condition is causing the pulses.

Nevertheless it is something the TS needs to allow for in designing a reliable circuit.

 

This can be done with two transistor SR flip flop triggered by edges (not levels). The two series capacitors on A&B inputs ensures the SR will change the state during positive edges on A&B inputs only.

 

Use two monostable multivibrators controlling an S-R flip-flop.

I have come up with a control circuit. See attached schematic and scope image.
Channel 1 is the STORE signal and channel 2 is the RESET signal. The STORE
signal is supposed to tell pin# 5 of the CD4042 latches to hold the value on
the input and essentially freeze the display until updated. If I understand the
data sheet for the CD4042, the STORE (pin# 5) should be HIGH normally and
go LOW just to store a new count value.

But, when I connect this circuit to my counter circuit, it does not "freeze" the
display.

 

That is because it is a follow/hold device , not a latch device. And, as nearly as I can see, the signal flow in the drawing is from right to left. So to hold the data the hold command must constantly be held. That is why, during my whole career, I only used the CD4042 one time.

 

I have come up with a control circuit. See attached schematic and scope image.
Channel 1 is the STORE signal and channel 2 is the RESET signal. The STORE
signal is supposed to tell pin# 5 of the CD4042 latches to hold the value on
the input and essentially freeze the display until updated. If I understand the
data sheet for the CD4042, the STORE (pin# 5) should be HIGH normally and
go LOW just to store a new count value.

But, when I connect this circuit to my counter circuit, it does not "freeze" the
display.

Try using pin 6 output as it is, i.e without the inverter.

 

Try using pin 6 output as it is, i.e without the inverter.

Thx Sarah. Will do. Unfortunately it doesn't do the trick.