I was thinking about the member who was starting out experimenting with crystal radio sets. They wanted to learn about the differences between different types of diodes.

See discussion on crystal radio construction here:
https://forum.allaboutcircuits.com/threads/my-shortwave-radio-questions-and-discussion.184242/

So, just for fun I created this simple I-V curve tracer last night in within a couple of hours.
The design is fairly straight forward, a 555-timer circuit and a couple of op-amp ICs, plus an oscilloscope in X-Y mode.

Here is a sequence of photos to demonstrate what to expect.

The horizontal or X-axis is voltage V across the device.
The vertical or Y-axis is device current I.
Hence the slope of the line represents I/V which is 1/R.
Thus, a low resistance will have a steeper slope.

The scale on the X-axis is approximately 1V per division.

Short Circuit



Open Circuit



100-ohm resistor


1000-ohm resistor


From the resistance I-V curves, it is easy to determine that the Y-scale is 5mA/DIV.

 

1N4001 Silicon diode



1N34A Germanium diode



1N5817 Schottky diode



2.4V Zener diode

 

Red LED


Blue LED

 

And finally,

2N3904 NPN Si BJT (bipolar junction transistor)


(I do have a tunnel diode somewhere. It is always interesting to see the I-V curve because of the negative resistance, i.e. the slope is negative.)

 

I love curve tracers, but in this particular case I love even more your CS4125. My first oscilloscope is the CS4025 and I still have it. Need to "unbury" it from somewhere.

 

I have intentionally omitted commentary on each experiment. Each one warrants some discussion and is filled with learning opportunities. I am going to include this discussion at a later date.

 

I love curve tracers, but in this particular case I love even more your CS4125. My first oscilloscope is the CS4025 and I still have it. Need to "unbury" it from somewhere.

I suppose I selected this oscilloscope because I wanted to demonstrate that you don't need an expensive high bandwidth scope to do this. Secondly, I think an analog display with vector stroke traces looks better than a modern DSO for this application.

 

Indeed the analog XY mode beats the vast majority of DSOs.

 

any schematic or links to this?,i have one i made but displays pants on my dso,good on my old tek 453 tho.

 

Analog scope traces make me feel nostalgic -they have a certain kind of beauty that is digital scopes I have seen cannot match. I think it is the fact that the velocity of the beam at every instance modulates the intensity that is part of this beauty.

Indeed the analog XY mode beats the vast majority of DSOs.

On the other hand it seems that even the least expensive digital scopes are capable of what only very expensive analog scopes can do, and that is support variable image retention all the way to infinite retention.



Current as a function of voltage for a infrared LED. Horizontal axis is 200 mv/ division
and the vertical axis is 1 ma per division. The knee is seen to be pretty sharp at 1 volt (about 15 Ω).
In the case of this measurement, the oscilloscope was adjusted to place the origin in the
lower left hand corner of the screen.

This trace above was made with a "manual sweep", a potentiometer adjusts the voltage, meaning that the operator can set the voltage to anything within the range and then measure voltage and current with a DVM for precise measurements. Infinite retention of the scope allows the display of the entire curve.

This is particularly useful for observing self-heating effects on components where such pronounced effects occur.

 

I have a simpler curve tracer.
connect the component in series with a suitable value resistor across the output of a 230V isolating transformer.
connect the earth clip to the junction of the component and the resistor.
connect the Y probe to the other end of the resistor and the X probe to the other end of the component, and select XY mode, and Y invert.