How to create this output?

Thread Starter

rocafellachild

Joined Sep 2, 2016
2
Hello

I have a basic knowledge of gates and flipflops and have come across this problem.
I have Input 1 and Input 2 going into a circuit made up of simple logic parts(gates, transistors, flip flops) but no microcontrollers. I have one output. (see picture)
upload_2016-9-2_14-35-6.png
I want the output to be high when (Input1=1 and the rising edge of Input2). I want the output to be low when (Input2=0 and the falling edge of Input1).

I've been trying to figure out a combination of logic to see if I can get this output but I think I'm stuck. Can someone suggest an approach on how to solve a problem like this?
 

AlbertHall

Joined Jun 4, 2014
12,345
For the particular inputs you show this circuit will do the job. Is IN2 being high guaranteed to be only while IN1 is high?
upload_2016-9-2_23-15-12.png
 

AnalogKid

Joined Aug 1, 2013
10,986
For a NOR gate S-R flipflop, a positive level changes state. Use an extra NOR gate as an inverter for IN1 before the ff. Take the output from the ff with inverted IN1 as its input.

ak
 

AnalogKid

Joined Aug 1, 2013
10,986
Scott, there is no need for C2 or R5. Q1 collector can tie directly to the reset input. According to post #1, it is ok for the circuit to be sitting in Reset between events. Also no need for R2 because the input is driven in both directions.

ak
 

ScottWang

Joined Aug 23, 2012
7,397
Scott, there is no need for C2 or R5. Q1 collector can tie directly to the reset input. According to post #1, it is ok for the circuit to be sitting in Reset between events.
Thanks Ak.
I have had thought about that, but I'm not sure, because I just want to avoid the S/R have any chance to conflict, and I just found that I missed the waveform for /Vin1, when I redraw the waveform then it's quite clear, S/R have no chance to conflict.

Also no need for R2 because the input is driven in both directions.
I have had also thought about that, but I will keep it until the condition more clear.

Vin2TrigOuputVin1ResetOuput-02_ScottWang.gif
 

AnalogKid

Joined Aug 1, 2013
10,986
Thanks Ak.
I have had thought about that, but I'm not sure, because I just want to avoid the S/R have any chance to conflict, and I just found that I missed the waveform for /Vin1, when I redraw the waveform then it's quite clear, S/R have no chance to conflict.
What you end up with is an inverter in front of a positive-logic S-R ff, just like post #6.

ak
 

AlbertHall

Joined Jun 4, 2014
12,345
This gives the wrong output for the given waveforms when IN1 has gone low but IN2 is still high. The output for will be a copy of IN1.
Correction:
I wrote IN1 and IN2 the wrong way round - but the two nand gate circuit still doesn't work.
This gives the wrong output for the given waveforms when IN2 has gone low but IN1 is still high. The output for will be a copy of IN2.
 

hp1729

Joined Nov 23, 2015
2,304
View attachment 111494
Hello

I have a basic knowledge of gates and flipflops and have come across this problem.
I have Input 1 and Input 2 going into a circuit made up of simple logic parts(gates, transistors, flip flops) but no microcontrollers. I have one output. (see picture)
View attachment 111456
I want the output to be high when (Input1=1 and the rising edge of Input2). I want the output to be low when (Input2=0 and the falling edge of Input1).

(With swapped IN 1 and IN 2 ...) Is it necessary that IN 2 be high when IN 1 goes high to set the output high? Is it necessary that IN 2 be low when IN 1 goes low to set the output low?

I've been trying to figure out a combination of logic to see if I can get this output but I think I'm stuck. Can someone suggest an approach on how to solve a problem like this?
 
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