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The Ultimate Logic Probe

A small logic probe for CMOS and TTL circuits. Measures 5 states, detects pulses and can play different tones for the different states.

Looking back through some of the stuff I have built over the years I came across a number of logic probes. Some worked better than others. One used sound to differentiate logic states, others had a 7 segment display that showed more states than those that had dual color or multiple LEDs, some only handled TTL logic levels etc.

So in this project, I wanted to create the ultimate logic probe. It must have the following features:

- It has to be small enough to easily fit in your hand
- Be able to show LOW, HIGH and DON’T CARE states
- A display system that is orientated for easy reading when being used
- Have audible feedback for LOW and HIGH states
- Handle different logic families of devices eg: TTL and CMOS
- Be able to detect whether the probe is measuring a fast changing signal
- Have protected inputs for accidental over voltages.”

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