Multiplexer for Oscilloscope

Thread Starter

Mancoba1

Joined Nov 16, 2023
30
Hello everyone,

I'm new here and currently working on a project. Unfortunately, I'm not very skilled in digital circuit design and I'm trying to capture the switching behavior of the MOSFET. I'm attempting to build a demultiplexer to select the individual outputs that need to be displayed. Additionally, I want to first capture all signals and then display them simultaneously. Control will be managed through a LabVIEW program. The circuit should be capable of displaying 8 signals simultaneously using only one channel of the oscilloscope.

I'm not a native English speaker. Could anyone tell me how I can improve my circuit to achieve my goal or point out errors that need correcting?
I would appreciate any help. I hope my question is clear. Sorry for my imperfect English.
 

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dl324

Joined Mar 30, 2015
16,928
Welcome to AAC!
The circuit should be capable of displaying 8 signals simultaneously using only one channel of the oscilloscope.
This can't be done. One channel on a scope can only display one signal at a time.

What application is needed to open your attachment? An image or PDF would be better.

Is this project schoolwork?
 

Thread Starter

Mancoba1

Joined Nov 16, 2023
30
Thank you for the quick response. Oh, sorry, I forgot to mention that. I'm using EAGLE Autodesk version 9.6.2.! I've read that it's possible, but I haven't found an example that's useful for me.
 

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dl324

Joined Mar 30, 2015
16,928
I've read that it's possible, but I haven't found an example that's useful for me.
It's still not possible. Can you cite some sources?

Could anyone tell me how I can improve my circuit to achieve my goal or point out errors that need correcting?
Your circuit makes no sense. The D flip flops have no clock.

Schematic with unnecessary whitespace and colors removed:
1700156250945.png
 

DickCappels

Joined Aug 21, 2008
10,183
It is actually a multiplexer. I did a two channel adapter for my CRT scope about 50 years ago using bipolar transistors.

A CD4051 probably won't get you much bandwidth. How much do you need?

What Is the purpose of the D-Flip Flops?
 

Thread Starter

Mancoba1

Joined Nov 16, 2023
30
doesn't matter. I actually only need it for switching purposes. I also have a Lecroy oscilloscope. The D flip-flop is primarily there to store the signal. As you know, in a 4-bit multiplexer for example, when inputting 0101, output 5 goes high. However, if you input something different like 0001, output 5 goes low and output 1 goes high. I need the multiplexer to retain the output state similar to a flip-flop, so that when I switch from 5 to 1, 5 remains high until I send a different signal to it.
 

AnalogKid

Joined Aug 1, 2013
11,052
This can't be done.
Sure it can. How do you think logic analyzers get 16 traces on one CRT? Dual-trace scopes date back to the 1940's and they had only one set of deflection coils/plates.

To the TS: This is not a task for a beginner. It is a difficult job that would take an experienced designer months to get right (the alternate/chop and trigger parts are actually much harder), but the concept is pretty straightforward. In parallel with an 8-channel multiplexer for the signals, have an 8-channel multiplexer with stepped DC voltages at the inputs. Sum the two so you get one signal and one offset at a time, and sum them into the deflection circuits

The back of my brain says that there were hobby magazines back in the day with this type of multi-signal adapter as a construction article. Popular Electronics / Radio-Electronics / etc. If someone knows the issue, I probably have it in my PDF library.

ak
 

dl324

Joined Mar 30, 2015
16,928
Sure it can. How do you think logic analyzers get 16 traces on one CRT? Dual-trace scopes date back to the 1940's and they had only one set of deflection coils/plates.
Go back and read what the OP asked for. He wants to add external circuitry to display 8 signals simultaneously while using one channel on the scope.

With circuitry internal to the scope, this can be done, but it still requires separate inputs for each channel. I have a 7D01 logic analyzer for my 1970's Tektronix scope that can do this. It can display 16 channels, but it requires 2 pods with 8 channels each to do it. It also has a formatter that can display the signals as 1's and 0's.

To do that, the plug-in replaced both vertical amplifier slots and one time base slot so it could control horizontal sweeping to display the multiple traces.

What the OP has asked for is impossible with his simplistic approach.
 
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DickCappels

Joined Aug 21, 2008
10,183
To the TS: This is not a task for a beginner. It is a difficult job that would take an experienced designer months to get right (the alternate/chop and trigger parts are actually much harder), but the concept is pretty straightforward. In parallel with an 8-channel multiplexer for the signals, have an 8-channel multiplexer with stepped DC voltages at the inputs. Sum the two so you get one signal and one offset at a time, and sum them into the deflection circuits
In my case, I did not really know what I was doing but it only took a week or two to design and get it working. The challenge here might getting the bandwidth"up there" and getting the chop rate right, or better yet having a variable chop rate.

@Mancoba1 Is this for looking at analog or digital signals?
 

Thread Starter

Mancoba1

Joined Nov 16, 2023
30
Hello everyone,

I wanted to output 8 signals simultaneously using just one channel of the oscilloscope. To achieve this, I looked into this approach and attempted to tailor it accordingly. Could you please take a look and let me know if these adjustments would work?

Realizing that the square wave oscillator and the divider circuit aren't necessary for toggling the "S0" and "S1" pins sequentially to momentarily select Channel 1, then Channel 2, and so forth, I removed them. Instead, I integrated my connection for my NI USB DAQ for control purposes. Would this circuit now be usable, or is something still missing?
"I'm using EAGLE Autodesk version 9.6.2"
source: https://www.learningelectronics.net/circuits/four-channel-oscilloscope-adaptor_18.html
 

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AnalogKid

Joined Aug 1, 2013
11,052
To be clear -

Do you want to see all eight signals simultaneously on one display, or select only one signal at a time?

Please post a larger image of the schematic.

ak
 

nsaspook

Joined Aug 27, 2009
13,292
Hello everyone,

I wanted to output 8 signals simultaneously using just one channel of the oscilloscope. To achieve this, I looked into this approach and attempted to tailor it accordingly. Could you please take a look and let me know if these adjustments would work?

Realizing that the square wave oscillator and the divider circuit aren't necessary for toggling the "S0" and "S1" pins sequentially to momentarily select Channel 1, then Channel 2, and so forth, I removed them. Instead, I integrated my connection for my NI USB DAQ for control purposes. Would this circuit now be usable, or is something still missing?
"I'm using EAGLE Autodesk version 9.6.2"
source: https://www.learningelectronics.net/circuits/four-channel-oscilloscope-adaptor_18.html
Nope, won't work as currently designed. You need a separate DC offset/vertical position adjustment for each input channel so they don't overlay on top of each other as selected by the multiplexer.
1700236990944.png
Using Eagle on your schematic file.

On a classic CRT analog scope there are two display modes to increase the number of signal display lines in Multi Trace Operation
https://www.physics.udel.edu/~nowak/phys245/Labs/Oscilloscope.html
There are two modes of dual-trace operation available on most oscilloscopes. The CHOPPED mode is the more useful one at low frequencies. In this mode, the beam alternately displays the two signals. The switching occurs at a relatively fast rate (2 microsec in the Model 2120 you are using) with blanking in between, so that all that should be seen on the screen are the two separate traces. The other dual-trace display mode is called the alternating mode. In this mode the output of CH1 is displayed for a full sweep, then the output of CH2 is displayed for a full sweep, and so on. When the two inputs are repetitive and synchronized this leads to a stable display. You can observe the difference between the chopped and alternate modes by looking again at the 6.3 V ac signal, first with a slow timebase setting of 5 ms/div and then with a much faster setting, while switching between the ALT and CHOP positions.
Alternate: Sweeps each compete line in sequence. Four lines takes 4 sweeps so the signals are not totally synchronized unless exactly repetitive.
1700237200715.png
Chop: Quickly switches between each line per sweep. 4 lines takes 1 sweep for signal synchronization but the actual signal displayed per line shown in discrete segments. Less noticeable when viewing slow signals.
1700237400140.png
1700238405836.png
Making this working for a nice display all depends on the phosphor/eye persistence to have a usable display. What would it look like on a modern digital scope?
 

Thread Starter

Mancoba1

Joined Nov 16, 2023
30
Do you want to see all eight signals simultaneously on one display, or select only one signal at a time?
Yes, I'd like all eight signals to be displayed simultaneously on the screen. This means I want the ability to select each of these signals individually and display them on the oscilloscope. I hope my problems and questions are understandable.
 

dl324

Joined Mar 30, 2015
16,928
Yes, I'd like all eight signals to be displayed simultaneously on the screen. This means I want the ability to select each of these signals individually and display them on the oscilloscope. I hope my problems and questions are understandable.
I don't think you've thought out what you're asking for. Displaying 8 traces on a scope doesn't give you much flexibility in vertical resolution. To make it useful for anything other than digital signals, you need to be able to vary vertical sensitivity for each channel. Once you do that, you need to be able to display vertical sensitivity for each channel independently. You'd also need to be able to offset them independently.
scope4traces.jpg
I can imagine how ugly the display would be on a digital scope.

Without control of the horizontal sweep, you can only chop the signals.
 
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