Back in the November 1998 edition of SILICON CHIP,
we described a very handy 3-LED Logic Probe.
The circuit is just as viable today as when it was published
six years ago and literally thousands of kits have been sold. That’s no
surprise: a logic probe is one of the "must have" test devices in any
hobbyist’s, technician’s or even engineer’s test equipment armoury.
What’s more, it’s cheap – so it’s an ideal beginner’s or school
project (not to mention one that will come in very handy over the years)!
One IC, three LEDs and a sprinkling of other components are all it takes to make a versatile Logic Probe. At left we are using the probe to check out the very first project ever published in SILICON CHIP, a 1GHz Digital Frequency Meter from November 1987. Yes, it still works perfectly!
So why re-invent perfectly good wheels and present it once
Simple: one of the suppliers of the afore-mentioned kits,
Altronics, reasoned that the it could be be made even better by re-designing the
PC board to a handier shape, adding a few extra (low-cost!) components to
provide better input protection, moving the supply on-board and finally, housing
the probe so it was much more like . . . a probe!