Resolve Circuit Conflict #2

Thread Starter

Hobbyist92

Joined Dec 17, 2020
25
Tektronix 1052B oscilloscope is a digital scope. You can record single shot events down to DC.
Set your scope to NORMAL trigger or SINGLE trigger and look for a single event.

Another way of testing your circuit is to use a faster clock signal into the 74LS74 flip-flop to give you higher repetition rates on the oscilloscope. Trigger the scope on the output of the 74LS74 flip-flop on CHAN 1 and look at the outputs of the C-R one-shot circuits on CHAN 2.
The circuit just doesn't work. Is there not a better circuit than this? I just joined AAC as I am having difficulty with this
circuit as well.

Moderator edit: New thread created from another thread.
https://forum.allaboutcircuits.com/threads/resolve-circuit-conflict.174990/
 

MrChips

Joined Oct 2, 2009
23,511
The circuit just doesn't work. Is there not a better circuit than this? I just joined AAC as I am having difficulty with this
circuit as well.
That response is not good enough.
Without jumping to conclusions why don't you describe how the circuit works and does not work.
How do I know that you don't have a missing wire, a wrong connection or a wrong or bad component?
You have to develop your own trouble shooting skills if you hope to move forward.
 

Thread Starter

Hobbyist92

Joined Dec 17, 2020
25
That response is not good enough.
Without jumping to conclusions why don't you describe how the circuit works and does not work.
How do I know that you don't have a missing wire, a wrong connection or a wrong or bad component?
You have to develop your own trouble shooting skills if you hope to move forward.
I don't know about the original person's circuit but there are no wrong connections and I have used
three different sets of components. All I can say is that the displays are all unlit unless I disconnect
the frequency source to be measured and then the displays keep displaying random numbers.
 

MrChips

Joined Oct 2, 2009
23,511
We cannot trouble shoot two different members' circuits on the same thread.
You will have to show your own circuit here.
 

MrChips

Joined Oct 2, 2009
23,511
I used the same circuit as I have been following radioshack's thread which is a modified
version from Forest Mimms.
Yes, but following a printed circuit off the internet is a different thing than debugging a physical circuit on your workbench.

Just to give examples, we have helped people who would report a DMM reading of 40V and they had failed to observe that the voltage was -40V, or that the meter was set to AC range and not DC range.

We cannot assist if someone reports that the circuit is not working. It can be defective for 100 reasons. Just saying.
 

andrewmm

Joined Feb 25, 2011
1,462
I used the same circuit as I have been following radioshack's thread which is a modified
version from Forest Mimms.
Hello @Hobbyist92

I'm sorry you seem to be suffering on the forums, some times people try to help in ways that can seem assertive,

Seems this thread is split from a previous one,
so maybe you can help us get up to speed.

Can you post a picture of your setup ?
Can you post a schematic.

Then, give us a hint please as to your experience so we can gauge our response ,

good luck,
 

Thread Starter

Hobbyist92

Joined Dec 17, 2020
25
Yes, but following a printed circuit off the internet is a different thing than debugging a physical circuit on your workbench.

Just to give examples, we have helped people who would report a DMM reading of 40V and they had failed to observe that the voltage was -40V, or that the meter was set to AC range and not DC range.

We cannot assist if someone reports that the circuit is not working. It can be defective for 100 reasons. Just saying.
ok. what do we need to do here to figure this out?
 

Thread Starter

Hobbyist92

Joined Dec 17, 2020
25
Hello @Hobbyist92

I'm sorry you seem to be suffering on the forums, some times people try to help in ways that can seem assertive,

Seems this thread is split from a previous one,
so maybe you can help us get up to speed.

Can you post a picture of your setup ?
Can you post a schematic.

Then, give us a hint please as to your experience so we can gauge our response ,

good luck,
TY Andrew

Here is my circuit. all wiring has been checked numerous times. Tried multiple sets of
components. I have no trouble-shooting experience at this point. Attached is my schematic.
 

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MrChips

Joined Oct 2, 2009
23,511
I should also add, if you wire a circuit and it works first time then you would have missed a perfect opportunity to enhance your knowledge and analytical problem solving skills.

When things don't work is when you really start to learn.
 

Thread Starter

Hobbyist92

Joined Dec 17, 2020
25
what test gear do you have ?

can you post picture of the actual circuit as well please, as this is very helpful.
Test gear=> triple power supply, arbitrary function generator, dmm, and 2 channel digital scope, all new stuff.
I am not proficient with the scope yet.

Here are photos. Not so great but I can't get them any better.

The first protoboard has a 10Mhz square wave oscillator using a 74HC04 and a 74HC14. This is followed by 5 74LS90's
to divide down to 1Hz. I used the 74LS90s rather than 3 74LS390s and 1 74LS90 in case I required different ranges for
the time base in the final design.

The second and third protoboards contain the five display circuits made up of 74LS90s, 74LS375s and 74LS47s
 

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Thread Starter

Hobbyist92

Joined Dec 17, 2020
25
In the last column of the first protoboard is a 74LS74 flip-flop and a 74LS00 NAND gate that make up
the gate control circuit. Below them is a 74LS14 that causes the display to reset zero on power-up.
The component in that column is a 74LS32 since the display can be reset by either the gate control
circuit or the power-up circuit.
 

andrewmm

Joined Feb 25, 2011
1,462
Wow,

Scope is a good tool,
Suggest you set a few different waveforms on the Arb function gen you have, plugged into the scope and see if you can see them as you expect, right frequency and amplitude.

So once you are comfortable with scope,

debug technique is divide and conquer


scope,
can you see the frequency to measure, is it the right frequency and voltage.
1hz timing ref, is it the right frequency and voltage.
output of the 74ls74, is the voltage and frequency you expect.
output "to counter input" , is it the rigth frequency , voltage and has gap when you expect ( two chanels on scope )
 

Thread Starter

Hobbyist92

Joined Dec 17, 2020
25
Wow,

Scope is a good tool,
Suggest you set a few different waveforms on the Arb function gen you have, plugged into the scope and see if you can see them as you expect, right frequency and amplitude.

So once you are comfortable with scope,

debug technique is divide and conquer


scope,
can you see the frequency to measure, is it the right frequency and voltage.
1hz timing ref, is it the right frequency and voltage.
output of the 74ls74, is the voltage and frequency you expect.
output "to counter input" , is it the rigth frequency , voltage and has gap when you expect ( two chanels on scope )
Hi:

I have taken the control circuit apart. The circuit (I realize that it won't work as is) appears as per the attached
schematic. I have also attached the scope image. I am using a 100 Hz time base but the frequency on the circuit
is only 50 Hz due to the flip-flop dividing by 2.

Some how I need to obtain two separate outputs after the flip-flop, one for the rising-edge pulse and another
for the falling-edge pulse.
 

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andrewmm

Joined Feb 25, 2011
1,462
so why do you need the divide by two then ?
what would the pulse you show look like if you just had a buffer in place of the divide by two ?
 
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