"Super Octopus" and ESR Test Adapter

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The circuits and ideas found elsewhere on this web site can be put together to form a cheap, compact and relatively simple test adapter for use in testing components for Voltage vs. Current characteristics and ESR. It can be used with almost any old analog scope, even so called "boat anchors" from the 1950's. The main requirement is that it have an accessible input to the X-axis amplifier.

I don't know when I'll get around to making it. Here are the basics:

A simple two pole- double throw switch could be used to switch the test probes between curve tracer and ESR modes.

The 100 kHz upper frequency is arbitrary. At higher frequencies the following problems would arise:

Design of the sine wave generator would be more complex.
Lead lengths and other construction details would become important.
The possibility of generating radio frequency interference increases.

Note that the ESR part of the diagram has an output lead for the scope's external trigger. I have not found this detail elsewhere, but in theory it offers the following advantage:

One limitation of most ESR testers is that a real good capacitor and a shorted capacitor test the same! By using the sine wave generator to trigger the time base sweep, the phase shift should occur on the oscilloscope display when a good capacitor is tested. This would be -90 Degrees for a large capacitor.

The resistor marked "?" will depend on the generator voltage. The 5 & 20 Ohm resistors in the ESR circuit should be of the power type, in case of surges from charged capacitors.

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