The clip:bit - An Addon for the Micro:bit

I’m still writing this article, expect missing content! -John

This work was published at IDC’23!^[1]
See the paper and poster here:

• Supporting fieldwork for primary education with computing – micro:bit, clip:bit and game controllers.^[2]
• Introducing Classroom Cloudlet: a mobile, tangible, and transparent approach to Internet of Things education.^[3]

Dear reader, please be kind to me on this one. For whatever reason, many of the components on this design have been particularly impacted by the ongoing (mid-2023) chip/parts shortage, and it caused me to have to replace rather a lot of the ones I wanted to use with nearly-alike alternatives, which does rather leave the board in a state which might look a bit strange to those of you in the design game.

…

Circle Intersection is a Pain!

This wasn’t very painful, but getting a contiguous line along a series of arcs in KiCAD takes a certain amount of finesse; an amount that I did not have at the start of this work, and resulted in some messing around to get the circle paths to line up in such a way that I could make KiCAD snap the arc segments together for a smooth cloud shape.

The trick, should anyone want to replicate this in their own work; is to enable grid snapping for your circle templates on a user# layer, then turn all snapping off to trace over the templates where you actually want your silkscreen/edge cut lines to be, otherwise KiCAD will do everything in its power to try and snap you to stuff you don’t want. The grid, pads, other lines, the center mark, horizontal/vertical alignment points… resulting in not-quite-perfectly-joined paths that will make the DRC hate you.

Better Routing Decisions

There are several places on the board where rushed decisions caused more trouble than they should - here for example I should have rotated the driver chip for the 7-segment displays 90 degrees left OR right, then routed out the side of the chip rather than resorting to the slightly ugly traces under the chip.

The rotation would have caused the LEDs mappings for each segment to change, but as these would be defined in software anyway, this is a non-problem and should have been corrected at the design stages.

Oh well… it does work, and in some senses protects the traces from damage by moving them closer to the center of the board, rather than having to be right at the left-hand edge.

I don’t miss placing all those resistors though! Yeesh!

The Power Switch

Another issue was with the side-actuated power switch, again added at the end of the design process, and I was forced to pick a part that I could actually find stock of (at the time of writing, the chip/component shortage is still a very real annoyance). Unfortunately a combination of slightly too thin mounting pads, and poor mechanical construction of the switches results in many of them being damaged by users.

One option that I should have perhaps explored further is to toggle the power through the insersion/removal of the micro:bit itself - there are additional traces for power, so routing through a set of pads on the edge connector is possible, but in this design would have resulted in some long power traces running up the back-side of the board to support this. At the time, I thought that this was too risky as long traces on a surface that could be placed on rock, or other abrasive surfaces would likely just be a recipie for disaster, but for v4 I’m absolutely moving to that design to remove the switch!

pxt-clip-bit^[4]
pxt-paged-data-log^[5]