micro:bit edge connector expansion board retainer clip

The problem

I use PCB expansion boards to plug my micro:bit into for a recent project. The micro:bit has connection pins printed along the edge of the board. This is called an ’edge connector’. Have a look here if you are not familiar with the micro:bit board. This edge connector plugs into an edge connector socket on the expansion board. The two components can be easily separated.

As I give the finished devices to other people to use, I need a way to stop the micro:bit from being easily removed from the expansion board. The micro:bit connector is not keyed, so it could be replaced upside down. Then Terrible Things will Happen.

The solution

I designed and 3D printed a clip that hooks over the back of the expansion board’s edge connector socket and plugs into the 4mm holes near the micro:bit’s edge connector. This clip prevents the micro:bit from being easily removed from the expansion board.

Please find a screenshot of the widget, taken from the 3D design software OpenSCAD used to design it, below.

The photo below shows the clip attached over the top of an expansion board edge connector socket, connecting the micro:bit board to it. You can see three of the five 4mm holes that are next to the micro:bit’s edge connector half exposed, sticking out of the black edge connector socket of the expansion board. The 3D printed clip slots into the two outer 4mm holes.

A side view of the retainer is shown below:

The retainer shown in the photographs was printed at the ’low quality’ setting of my printer as I am still refining the design. The expansion board that the micro:bit is plugged into shown in the photographs is the Sparkfun micro:bit breakout board.

Background

For my flex sensor project I need to add some functionality to the BBC micro:bit. To achieve this, I plug the micro:bit into a small expansion board. The expansion board is designed to allow a few components to be soldered onto it which connect with the micro:bit through the edge connector socket on the expansion board.

Design

I use OpenSCAD, which allows the design to be entered through programming. There are many 3D CAD packages available. I use OpenSCAD as the method of programming in a design goes down my ‘brain-hole’ more easily than the different methods of design entry used by the other packages I have tried.

Use the design software that suits you

3D printing

I used my Creality CR10 mini printer which I first wrote about here to 3D print the clips. On the ’low quality’ setting the print takes about 10 minutes. This print time is a little misleading though. You need to allow for the print bed and nozzle to warm up. Then it is best to leave the finished print to cool down so it comes off the print bed easily. Hacking away with the flat bladed paint remover tool to remove a still-warm print from the print bed risks damaging the print and marking the print bed.

How you can replicate this product

I put the OpenSCAD design file for the retainer in the project GitHub repository here.

The end

The retainer clip will be incorporated as part of the casing for the device. Currently, I have a 3D printed case over the expansion board and a silicone cover over the micro:bit. I will add the retainer clip to the case that goes over the expansion board.

Comments and improvement suggestions are welcome.