Home-Inspired Innovation to Create the Finest Multimeter Probes

By: Robert Fitzgerald
Senior Consultant, Signal Processing

6th December 2019

2 minute read

During the course of my career in Electronics, almost all semiconductor components have become increasingly smaller. Whilst this has brought many benefits in terms of size, performance and power consumption, the task of debugging circuits has become much harder. Long gone are the days when you could attach a friendly IC test clip over a 16 pin DIL IC to probe key signals.

Magnifying the problem

The inexorable march of long sightedness has provided a double-whammy and made this task even harder. Help is at hand thanks to head mount magnifier glasses, which even with an LED only cost around £10.

In-circuit test techniques such as JTAG have helped, but sometimes there’s no substitute for actually debugging your PCB with a multimeter or scope.

If you’re lucky enough to be probing an IC that actually has pins or a QFN package where there is a tiny area of exposed metal to access, the probes that come with most multimeters are usually too broad at the tip to ensure you’re on the pin you want rather than shorting out the adjacent pin and making matters a whole lot worse!

Many well-known suppliers offer test leads with fine tips buts none were quite sharp enough – and they’re not cheap.

Inspiration!

Salvation came from the unlikely source of my wife’s needlework kit. Whilst rummaging through it looking for some elastic I was stabbed by a needle. Upon removing offending item from my finger I realized that being made of metal and sharp enough to draw blood, it was just what I needed for circuit debugging.

Said needle was promptly soldered to a 4mm banana socket with plenty of heatshrink to make the connection sufficiently robust and the net result is shown below:

Probing a 0.5mm pitch quad flat pack IC is now slightly less precarious.

The end can be made even sharper with the aid of a file but beware such probes are very sharp as I found to my initial cost.
As every Engineer knows, it’s the magic smoke that makes all semiconductors work and these probes have helped me keep it on the inside and aided fault finding.

How have you solved problems in unexpected ways?