Monthly Archives: June 2015

Inexpensive logic analyzer

Cypress has a little USB-interface micro called the EZ-USB that can stream the state of its GPIO pins to a host computer.  This chip was used by Saleae in their original Logic product, making for a simple, inexpensive logic analyzer.

Now, it turns out, there are cheap dev boards for this chip all over eBay (in the sub-$8 range) that can be loaded with some open source firmware from the Sigrok project to turn them into a similar logic analyzer.  Unfortunately, the EZ-USB chip is a 3.3V part, and has no protection on its GPIOs.  Fortunately, there are plenty of 5V tolerant non-inverting buffers out there, such as the 74LCX245 I picked.  Add some 100-ohm current-limiting resistors, and you’ve got pretty much what you need.  So, I designed a board and submitted it to OSHPark.  Parts-wise, it’s pretty easy…two 2×10 female headers (soldered facing downward, it made the layout easier), a right-angle 1×9 male header for the probes, 8x 100ohm 0805 resistors (easy hand soldering), and a 20SOIC 74LCX245.

Can’t wait for the boards to get here so I can try it out!