Test Adapters for Oscilloscope

A simple and cheap adapter has been designed for the purpose of converting any oscilloscope into a component tester.

Using this adapter can display the current vs. voltage characteristics of a component on an oscilloscope’s screen. It was named as Octopus because the first assembly was so messy with wires sticking out all over the place and the classic version of the Octopus consists of only a filament transformer and three resistors.

In this design, an old wall wart was used rather than using a conventional transformer for the signal source. It was rated at 3.3VAC and originally made for an early TI calculator. Under light loading, the reading on the voltmeter showed an output of 7.8VAC. A 1K Ohm resistor in series with a 100K potentiometer was used rather than using a fixed reference resistor and the dial was calibrated for resistance in Ohms.

To prevent applying a reverse voltage to polarized capacitors during testing, a diode D1 is added to one of the 10V settings. A voltage divider is formed by R1-R4 resistors to allow selection of 3 different voltage levels for testing. The 3V was chosen enough for checking the LEDs.
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