octopus curve tracer

Posted on Feb 7, 2014

This project involves the construction of a low-cost curve tracer that is suitable for testing a wide variety of electronic components both in-circuit and out of circuit. It is easy to construct and extremely useful for finding defective parts, especially semiconductors, in electronic devices. The octopus is used in conjuction with an oscilloscope

octopus curve tracer
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set to display in X-Y mode. It displays voltage across the test probes on one axis and current through the probes on the other axis. A scope with both Horizontal and Vertical inputs (X-Y mode) is required. This is my version of a circuit that has been around since at least the 1960s, I added the ability to select voltage taps on the filament transformer and adjust the amount of current through the probes. Power is applied to the step-down transformer through a 1 amp fuse and a power switch. The transformer has output taps at 4V, 8V, 12V and 16V. If you can`t find an equivalent transformer, a more common 6V/12V transformer will work. The voltage select switch allows one of four voltages to be selected. The current limit variable resistor selects the maximum current through the test probes. When the probes are open, the scope will display a vertical line, when the scope probes are shorted, the scope will display a horizontal line. The octopus places a constantly changing sine wave voltage across the probed device. The horizontal axis shows the current through the probes and the vertical axis shows the voltage across the probes. As the sine wave changes, the scope trace loops around in accordance with the associated current and voltage readings from the probe. Probing different electronic components will produce a variety of unique scope patterns. The octopus was built into a deep 4"x4" electrical utility box, as shown in the...

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