Electronics, music, electronic music! general geekery


Casio SK-1 Mods!!

It's been a while since I've bent any circuits, so this week I did some work on my Casio SK-1. Specifically, I installed a Universal MIDI Retrofit kit from, and added some leads from bend points on the CPU pins. Here are the highlights in case you're thinking of retrofitting an ancient keyboard with MIDI, or circuit bending an SK-1. The MIDI retrofit went very smoothly. The kit is very well documented, and it was a joy to build and install. It worked without a hitch the first time I powered on. In this shot you can see the installed circuit board sitting in the spot that was once occupied by the speaker. The kit includes a square of adhesive to hold the board in place, but on the SK-1 the screw holes for the speaker line up closely enough to screw in one side of the UMR board. As you can see it is mounted quite securely:

Athough the UMR board connects to the SK-1's 5V line, it must be powered on a few seconds AFTER the SK-1 is powered on. Therefore, you have to add a switch to the positive line. I used a funky green pushbutton I had lying around. I also mounted the LEDs externally which is really essential to see if the MIDI unit has successfully powered on. [Update: After using this a few times it looks like interrupting the 5V line has some odd side effects. In order to turn off the unit I have to cycle the power switch a couple of times.]

This next photo shows the MIDI jack, LEDs, and power switch:

Connecting the UMR board to the ribbon cable connector was actually pretty easy. I harvested some nice thin little wires from an old printer cable. As a bonus, one side of the printer cable is a male 25-pin D-sub which I will save for later use. You can get old computer gear for cheap at thrift stores. The installation instructions for the UMR have a nice table that shows which wires from the board go to which spots on the SK-1 circuit board. The SK-1 circuit board is conveniently marked to show you which pin is #1, and which is #12. Just match the wires and you're in business! This shot shows the connections:

Now it's time to move on to the good stuff: the bends! I decided to take the straightforward approach of attaching a lead to each one of the processor pins. I know there are many, many bends aside from the ones I did. However this is a nice approach since you've got 25 wires to connect up in any combination, which yields a satisfying amount of possible bends. Besides, I've got the MIDI kit working so nicely it would be a shame to burn things out looking for new bends. Plus I have another SK-1 for later. This photo shows each lead obediently curving its way to its own special spot on a 25-pin female D-sub jack. Now you can see where the recycled cable is going to go, eh??? Straight onto a breadboard I tell you!!! [Update: The D-sub cable turned out to be shorted out, so now I've got to find another. At least I got a whole bunch of wire out of it though!!]

Now I could just go and build a patch bay, or put some pots and switches into a case and call it a day. But oh, no, that just won't do. I have something else in mind. The frayed end of that recycled printer cable is poised to link into a world of wonder facilitated by things that rhyme with "smart, you Eno", and "Axe, I must PEE". All mounted in a clear plexiglas case, resplendent with multicolor LEDs. But I've said too much. Now if you'll excuse me, I'm going to resolder the battery leads and screw the case back together.

Update: Now I see why the SK-1 is considered to be one of the best instruments to circuit-bend. You can play it, and just keep hitting bend points over and over again. I have recorded some great new sounds and all I'm doing is shorting the bends on the exposed terminals of a male d-sub jack with a piece of wire scrap. I can't wait to hook this up to something more comprehensive, it's sure to be monumental.

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