We live in a day when it is very inexpensive to buy an oscilloscope, especially one with modest performance that hooks to a laptop. However, there was a time when even a surplus scope was out of reach for many people who liked to build things. A common alternative was the logic probe. At the low end, this could be an inverter and an LED, although it was more common to have a little extra circuitry to actually do a comparison to a reference voltage and present some indication of fast pulses — you might not be able to tell the frequency of a clock, but you could tell it wasn’t stuck. Of course, today with a microcontroller you can make a very sophisticated probe with less circuitry than a classic probe. We’ve seen a few takes on this and the latest is the DigiLogicProbe from [TheRadMan].
The probe is just a ATtiny85 board with a handful of components. A resistor and diode help protect the probe and the circuit under test. There are also a few LEDs and a buzzer. The rest of the project is software.
The probe, of course, can do the classic functions or even act as a continuity tester. [TheRadMan] has more plans, though. He’s looked at the venerable SuperProbe project which does the same kind of trick and can do things like read serial data, measure capacitance, inject pulses and drive servos, among other things. There’s also the Little Helper and doubtless others out there.
If you start following links to all these helpers you will find the hard part might not be the design, but finding a suitable case. Many times people will repurpose an old logic probe or similar device. A piece of PVC pipe is another common alternative. Then again, you can always fire up your 3D printer.