In 2010, MIDIboxer TK. made huge waves with his BLM (button LED matrix) 16×16+X. Never before had we seen such a mangle of duo LEDs, verowire and shift registers. The monome had been known for several years prior, as had smaller matrices for the SEQ, but the 16×16+X was a step further with its colourful LEDs and dedicated column, row and shift button. Arguably these pioneering devices inspired widespread development in commercial products such as the Novation Launchpad and Ableton Push.

TK.'s prototype was only ever meant to be that. In his words it took 40 hours and he was never prepared to do the same work again. Although the unit still works some five years later, the point-to-point wiring is somewhat fragile and the cheap tactile buttons are unergonomic. There were a few attempts at full PCB solutions, but the scale of the project is fairly daunting and sadly none eventuated.

My interest in a fresh start was piqued upon hearing of adafruit's UNTZtrument, which uses their own 4*4 silicone button pads. Years back we had considered pads from Sparkfun and Livid, but adafruit's are significantly smaller and cheaper. Rubberised buttons also have the best tactile feeling and don't click when they're pressed. One issue was the small internal space inside the button (only accepting a 3mm LED) so it was determined from the start to go for an SMT solution.

Initial development of the BLM was done by TK., as noted elsewhere. A 17*17 button array is scanned using SCALAR modules consisting of 74HC165 (DIN) and 74HC595 (DOUT) shift register chips, the latter as current sinks via BJT transistors. Additional 595 chips drive LED anodes, while the cathodes share the same sinks as before. In total five SCALAR modules are present, one for the left-most and bottom “extra” column and row, and four for the remaining blocks of 16×4.

In the BLM 16×16+X PCB, the matrix is fully connected and all SCALAR modules are on-board, allowing for a cleaner build with less wiring, less physical space required and better signal integrity. A 4-layer PCB was used with one layer dedicated to ground/0V. There was also space to include four 75mm sliders which allow for additional control. The serial chains are brought out by a MIDIbox-standard J8/9 2*5 DIL header with the SC (clock), RC (latch), DIN and DOUT signals, along with +5V and 0v/ground. These may be interfaced with a MBHP Core8 or Core32 module, but most users will stick to the tailor-made miniCore (see later).

For minimal external cabling, the BLM connects to a SEQ v4 via an 8-pin DIN connector. This combines MIDI in, MIDI out and power; the communications protocol sent and received by the BLM is standard MIDI. Most users will incorporate a Quad IIC board into their SEQ case, which is the simplest way to arrange the DIN8 connector, optocoupler and header pins.