Op Amp Contest: Clever Continuity Tester Tells You Where The Problem Is

Continuity testers found in most multimeters today are great tools for finding broken connections and shorts. But once you find the short, it’s up to you to figure out where in the circuit it is. It’s tedious work on a big PCB with hundreds of components. [John Guy] It aims to facilitate this task with Continuity tester with adjustable beeper Depending on the resistance measured in the circuit. Tracking a short is probing multiple points along the track and observing if the pitch goes up or down.

This circuit is based on a single AD8534 quad op amp chip. The first stage measures the voltage of the circuit under test in response to a small current and amplifies it. The resulting signal is fed to a voltage controlled oscillator (VCO) consisting of one opamp connected as an integrator and another opamp acting as a comparator with hysteresis. Opamp number 4 amplifies the resulting square wave and drives the speaker. A low-pass filter removes high frequencies, making the sound pleasing to the ear.

[John] Special attention has been paid to the PCB design for ease of assembly, despite having a large number of SMD components on a small board. The parts list is also posted on the silkscreen on the back, so anyone can assemble it without the attached documents. The resulting board can be placed in a laser-cut acrylic case, transforming it into a neat handheld device that’s sure to fit in any engineer’s toolbox. Measuring resistance by sound is not as accurate as using a full 4-wire setup with an ohmmeter, but it is much quicker and easier if you just want to find those annoying solder bridges hidden somewhere on your board. It gets easier.