Building One Test Fixture To Rule Them All

Test and programming fixtures are great time-savers for anyone who needs to deal with more than a handful of PCBs. Instead of plugging in connectors (or awkwardly holding probe tips or wires) to program some firmware or run tests, one simply pops a PCB into a custom fixture with one hand, and sips a margarita with the other while a program decides whether everything is as it should be. Test fixtures tend to be custom-made for specific board layouts, meaning one tester is needed per board or device type, but this work is easily justified by the huge time savings they offer.

An inserted PCB sits atop the thick acrylic piece, with pogo pins making contact from below. Generous space on the left and right make sure there is clearance for any mounted components. Visible near the bottom of the green board are output LEDs, and two touch-sensitive pads.

But the fine folks at Sparkfun’s quality control department figured they could save even more time by exploiting common design features across different boards, and shared details about designing a single test fixture flexible enough to handle multiple board types and designs.

The test unit looks like pretty familiar stuff at first glance: some hardware responsible for running the test program, laser-cut acrylic jig to hold a test PCB in a consistent position, spring-loaded pogo pins to make temporary electrical connections, and LEDs to clearly indicate PASS and FAIL states. The clever part is the way the fixture is designed to accommodate multiple board designs, and how it uses several 74LVC4066 quad bilateral switch ICs to take care of switching which pogo pins are connected and to where.

As mentioned, to be compatible with multiple boards there must be common design elements to exploit. In Sparkfun’s case, the through-hole connections on their breakout boards are all in a row with standard 0.1″ spacing. By using the aforementioned pogo pins and 4066 ICs, different pinouts can be accommodated and multiple board types can be used without any need to swap to different test hardware.

Test and programming fixtures, being one-offs, tend to have a lot of space for creativity and often show clever design or re-purposing of parts. Our own [Bob Baddeley] explains all about them here.

3 thoughts on “Building One Test Fixture To Rule Them All

    1. You poor thing, did the big bad capitalists hurt you? Maybe if you complain some more it’ll make you feel better.

      I’m sorry, but the “breakout boards are a scam” crowd has gotten really wearing over the last decade of hearing them whine. I find the things useful for prototyping; maybe I’m just more in the target market, since I’m rarely building more than a one-off device.

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.