Pogo pins are spring-loaded electrical contacts. The spring allows the pogo pins to form a solid electrical connection during testing, without having to otherwise solder up the device under test (DUT).
The photo above shows an assorted selection of the pogos we use here in the shop. Click through for a larger version of the image. As you can see, they come in a variety of shapes and sizes. They also have different types of “crowns”, which allow contact with various connectors (plated through-holes, exposed copper pads, solder blobs, etc.)
This photo shows part of the inside of a pogo pin. Pogos are typically made of gold- or tin-plated steel, just like headers. You can see here where I filed away some of the gold on the surface around the window.
In this photo, I’ve depressed the pogo part of the way, so that you can see the base of the plunger pushing down on the spring. To keep the plunger from popping out, there is a stop ring molded into the outer casing of the pin. You can see part of this ring in this photo, and even better in the photo at the top of the post. This ring is formed by pre-loading the pogo pin (compressing the plunger), and then putting the device through a rolling process.
Each board we test has it’s own testing jig. Some of these are constructed using permaprotos or our Arduino protoshields, and others are custom made. We use the custom board above for the Flora NeoPixels, because we test entire panels of 20 pixels at a time.
The NeoPixels are basically unidirectional shift registers that use a one-wire protocol. They have data-in and data-out connectors so that they can be chained. In the photo above, the arrows on the PCB indicate the direction of data, so that the test panel can be oriented correctly. Each 4-contact diamond group is a separate pixel, with the north and south pins being power and ground. This test requires a visual inspection — we check to make sure all the LEDs light up in all three channels.
Here’s a video illustrating how we test the Flora pixels with the pogo bed-of-nails:
Here’s a totally artistic photo of another test jig built on an Arduino Protoshield. This one is for the Flora Accelerometer/Compass sensor. This test is purely electrical. The Arduino runs through some test code to verify the device is working properly and yielding data within spec, and chirps the piezo if everything is OK.