More inputs by matrixing BU0836X

[jimbop]

I couldn’t find a description of this anywhere so thought it could be worth posting. Not difficult anyway but could help someone out I guess.

Leo Bodnar’s BU0836X is a great piece of kit and very simple to use. But if you’re going to bother building a control box then you want to do it right and obviously that means you want more than 32 digital inputs (i.e. buttons and switches). Well, I did anyway… So your options are either to buy another card or to matrix the card to allow double-inputs as described here.

A matrix on 23 of the BU0836X’s 32 inputs (allowing 9 of the 32 inputs for 3 additional rotary encoders) allows 276 inputs consisting of the 23 single inputs (Input_1, Input_2, Input_3 etc) and 253 unique dual inputs (Input_1 + Input_2, Input_1 + Input_3, Input_1 + Input_4 etc). You could think of Input_1, for instance, as Control and Input_2 as any other key. You can either map the inputs in the sim manually or you can assign them to keyboard inputs using Autohotkey, SVMapper, JoyToKey, Xpader etc.

The PCB is logically simple so I didn’t bother drawing a diagram and went straight to the circuits. Below is an extract showing the first input set of Input_1 combined with the other 22 inputs. Note that each double-input requires two diodes (I used 1N414 to avoid other circuits being completed. Luckily diodes are about the cheapest bit of electronic gear you can buy at just a few cents each. This set repeats 22 times reducing by one each repeat. I used a 300 x 150 mm PCB with 0.8 mm holes – works great. Click for full size:



Full two-sided board (grey is bottom, red is top):


Top only:


Bottom only:


If you can't manage a double-sided PCB then you can do the top layer only and link up the array using hookup wire. Pretty tedious though.