Theory of a DIY Analog Curve Tracer

There is a super easy circuit for turning a Analog Oscilloscope into some what of a curve tracer, it’s called a Octopus. Nothing more then a low voltage AC line and a resistor to handle the current.

Now what if you don’t have a Oscilloscope let alone a vintage Analog scope? Well the Octopus doesn’t need much resolution to give you a signal on the device under test. Should work fine with a old CRT television.

There are plenty of guides on turning a CRT TV into a so called Oscilloscope. However they’re very basic and do not do much other then connecting a audio source or a function generator to it.

Now if we add a two channel Amplifier to the Horizontal and Vertical coils of the CRT we can then get a typical analog scope view. However this is very low resolution and you might be able to also add a Attenuator to the input. From the input you would add the Octopus circuit.

Using something similar to this diagram we could add a Sweep and Octopus and just tap into the coils. Instead of powering the CRT from this circuit we would only use the Vert and Horz coils.


Instead of 240V on the B+ we would use a much lower voltage. Basically We would use the lower portion of the circuit and only need the X and Y channels.

We would also need this circuit.


This would add the Sweep for the horizontal.  From there we can add the Octopus.


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