HP545A Logic Probe Upgraded with FPGA Power

They don’t build them like they used to. Or so the saying goes. While the electronics of today are vastly more powerful than those made a decade (or four) ago, there may be an older test equipment format that you really like. Such is the case with the original HP545A logic probe, which, according to “retired” EE Robert Morrison, has the perfect form factor for debugging SMT circuitry. But...

At 45 years old, it just can’t keep up with 100MHz or faster signals. So he did what any ambitious engineer (with enough available time) would do and made an FPGA upgrade for it. The device utilizes a SparkFun Alorium FPGA board (which also appears to be retired) and a 74ALVC04 hex inverter IC for signal acquisition and processing, along with a 1.3-inch OLED screen to output probe results.

Morrison added buttons to the probe for user input, with long presses switching between different modes. The probe’s ground pin was also modified as a second logic input (accessed via a plug-in cable), which opens up its capabilities to I2C signals and more.

It’s a neat build, though one caveat is that it works in a simulated environment, but still needs real-world testing to verify its operation. Code, and even an STL file for mounting, are available, so you could run it through its paces and/or improve on it yourself. The code and electronics should work with other probes as well, though the holder will need to be altered.

Of course, if you’re still coming up with cool things, are you really a retired engineer? Can an engineer ever truly retire? For better or worse, I think many of us would prefer to leave this world with a calculator and (custom) logic analyzer in hand, even if we’re not getting paid for our efforts!