Wednesday, October 31, 2018


Another modular 4x4 experiment

A 4x12 matrix using 3 modular 4x4 matrix boards and powered by a Pro Micro.

The previous 4x4 boards were powered by an Arduino Micro, this one is using a Pro Micro. The Pro Micro has less data pins available so only 3 boards can be connected instead of 4. There are 2 pins left over, I used one (B5) for a backlight circuit like on a Gherkin. The other data pin is left for possible use with a WS2812B strip.

Fully assembled with a top PCB plate. LEDs are powered by a MOSFET and controlled by a PWM enabled data pin (B5).

I also made a plain bottom plate. The plates are held together with solder brides, like on the original 4x4.

Top plate, PCB and bottom plate connected with M2 spacers and screws.

You could just use the PCB and skip the plates. Use PCB mount switches and a piece of wood or aluminum as the base.

The mini USB connector can be installed on any of the 3 boards. The pigtail connects it to the Pro Micro.

If you want LEDs, the MOSFET has to be installed on the first board with the Pro Micro.

I added little nubs that interlock the boards. They may need to be lightly sanded so that they fit into the notches and the boards are flush together.

The edge connectors are in a similar pattern to the original 4x4. Only the top 3 sets of connectors are used for the keyboard matrix. The bottom pair are to pass power, LEDs and the extra data pin. DATA is the extra unused pin and FET is the MOSFET that the LED cathodes on each board connect to.

Gerber files, parts list and a json file for are on github.