ETI Project 120

Back in 1979 I built a logic probe which is still in use today. The circuit came from the December 1975 Electronics Today International and has proved invaluable over the years and for just about as many years I've been meaning to re-do the circuit board.

The time has finally come to take a look at it. I could simply produce a new circuit board from the ETI artworks or I could re-think it a little so I came up with a minature version, by using surface mount components the pcb is just 25x41mm (the original measures 46x56mm) and when cased it measures 32x46x20mm.

I kept the same case style except that it is opaque so the surface mount LED's shine through and also I prefer using E-Z-hooks to connect to a component rather than the original pen design but I'm sure a needle could be attached if required.

PCB layout.

As the board is densely populated I had the board assembled by JLCPCB except for the switch. The cost for this service, PCB, components and assembly worked out at around 5.00/board, less than 4.00 with a voucher. (2021)

Soldering the power and probe wires then testing it against the original. The new case is shown to compare sizes although the new case could be 10mm slimmer!.

Built into the case and just the crocodile clips and E-Z Hook to fit.

Project complete - Crocodile clips and E-Z Hook fitted.

My re-draw of the circuit diagram with current parts.

EasyEDA Project Page.

Circuit, BOM and Gerbers.