Sunday 3 January 2016

DIY MIDI Controller with LEDs

Possibly one of the least amazing titles for a blog articles! In these days where RGB LEDs feature on just about every specification list for MIDI Controllers, then the only difference is that it's a simple home-brew MIDI Controller - creatively mis-using a spare numeric keypad.

The numeric keypad is intended to be used with laptops that don't have separate number keys in a nice neat square form, and require the user to either use the buttons over the 'qwerty' row, or to do various extra key-presses to re-use other keys on the main qwerty keyboard. So the keys on the keypad just map into the standard key numbers as if this was a full external keyboard. To use the keypad as a controller, I have been working on a simple MaxForLive plug-in that intercepts the incoming key number messages and allocates them to functions in Ableton Live - this is still ongoing work, but the controller is finished, hence this blog entry!

The keypad as supplied is very boring: black plastic everywhere, and the only concession to RGB LED-ness is a red 'Num Lock' LED that isn't really relevant in this context. So this obviously needed augmenting. First task was to light up the keypad itself, and four blue LEDs did that very nicely. The numeric keypad came with a USB plug, so power was easily available, and I just added a few series resistors to the LEDs. I could have added more LEDs, but four was okay for this first iteration, and there is a definite limit to how much hot-melt glue you can use without waiting for it to cool down properly.

The flashing yellow circle came from a concert wristband that my son was about to throw away because the batteries had died, and so that was pressed into service (with an on/off switch). The flashing multi-coloured interior to the circle was one of those 'infinite mirror' displays where two mirrors bounce light back and forth many times giving an illusion of depth, and so that became the middle of the circle, again with a selector button to allow the choice of flashing mode.

The end result looks very flashy (deliberate pun!) but has one problem - the backspace and return key tend to be used in mot application UIs - and in Ableton Live the Backspace key deletes the active plug-in, which is usually the custom M4L plug-in, whilst the Return key tends to spawn a new version of the plug-in. Obviously these buttons are not very useful in a control context, and the simplest solution was to disable them - mechanically (you were expecting a software method, perhaps?).

 Disabling keys on keypads is relatively easy given the lack of travel of modern keypads - you just put lumps of blu-tack (or other similar slightly sticky substance) underneath them, so that pressing them doesn't result in any movement. Here are some photos showing bits of this process.

Prising keys off is usually pretty easy - I use a screwdriver. doing the blu-tack is easy, and putting the key back is normally just a question of pushing it back.

Please note that the lower cost the numeric keypad, the easier these types of mods tend to be. Levering out the keys on an expensive laptop (an Apple MacBook Pro for example) and trying to put them back with blu-tack underneath is definitely not recommended! (Just don't do it!)

To indicate that two of the keys were now disabled, I covered them with white typing correction fluid, something which used to be a standard home office accessory... I'm looking for a better solution, and 'sticky-back plastic' is definitely beckoning me!

And that's it. A spare (actually unwanted, although it sounded like a good idea at the time!) numeric keypad turned into something which looks like a MIDI Controller, and which may well be used when I iron the bugs out of the MaxForLive plug-in. In the meantime, it looks very good on stage, and isn't that one of the prime reasons behind all of those RGB LEDs anyway?

Now that I think about it, I probably didn't need to modify the keypad at all - I could have just assembled a few bits of LED toys and put them into a suitably technical-looking box and I'd have a stage box that smart-alecks and know-it-alls would look at and say things like: '...and there was this amazing home-brew controller...'. Maybe there's a business opportunity here?

[ Note that I'm not suggesting that you modify/wreck your own (or anyone else's) keypads, keyboards, laptops or anything else. I'm just showing that I sometimes do hardware as well as M4L! If you do make any modifications, then you assume full responsibility for them! ] 

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