Project: MicroLit – PCB V2


A couple of things went wrong on the first PCB. Firstly, the fab I used did not support V-grooves, which meant that instead of being able to mount the BBC MicroBit vertically by snapping off the top section of the PCB, it had to mount horizontally. Secondly, I needed to include level translation so that the MicroBit (which operates at 3.3V) could talk to the LEDs (which operate at 5V).

Level Translation

For level translation I used the 74LVC1T45 from Diodes Incorporated which is a single channel level converter in a tiny SOT563 package which is, as usual, unnecessarily small.


Level translator pinout

Vcc(A) was connected to 3.3V and Vcc(B) was connected to 5V. DIR was connected to 3.3V so that pin A was an the 3.3V input for the data from the MicroBit and pin B was the 5V output to the LEDs. The data sheet did not specify bypass caps but I added one to each of the 5V and 3.3V rails just to be safe.


Final PCB is similar to V1 but includes a level translator in the bottom right

PCB Bring Up

When I first was bringing up the board, it worked as expected – all of the issues with level translation went away… until the level translator chips started blowing up. Every time I replaced the level translator, it worked fine at first until I turned off the power to the LED strip via the MOSFET. Probing the 5V rail showed large 16V+ spikes during turn off.  I suspect the cause for this was the large inductance on the 5V rail due to the long LED strips. This was fixed by adding a large 10uF cap on the 5V rail, making use of the capacitor footprints I put on the PCB for the level translator bypass caps.

3D Printed Enclosure

I wanted to mount this board on the skirting around the ceiling of my bedroom so I 3D printed a small “enclosure” to put it in (it was not fully enclosed).

Screenshot from 2019-09-22 07-09-03

Enclosure design in OpenScad


Final board in 3d printed enclosure

To control the lights I had a second MicroBit on my desk that communicated over RF. For this I printed a MicroBit case which I found on the internet


As usual, all designs can be found on my GitHub.

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