SX-150 had released from Gakken. It's the almost first Gadget Synth in Japan. It's hard to track the pitch correctly for temperature drifts. but it small and cute. it gets me and makes me feel good.
When it had released from Gakken, RadioJankBox who live in Saporo had developed "MIDI-IF for SX-150". (He lives in tokyo, now)
I trace it and add mod to be able to use it as live performance.
Later, I bend it for Monotron. Some of values of parts should be changed but they are almost same. And SX-150 has no gate input, so I add some idea to use it for SX-150.
this package is only for board. you may need "#212 Connector set of MIDI-IF for SX-150" also to build it. Anyway check the schematic, first.
About battery, We use "006p" that 9v type.
Conecting with SX-150, there is white line at SPAN knob labeled "SX Pitch" is going to be connected with SX-150's stylus pen.
And You can find another white line line at the bottom of the picture comes from RATE knob's red line that labeled as "SX GND". This line should be connected with SX-150's GND. The spring at battery is the GND. And you can get it also from output jack's shield side. I put 3.5mm jack to get the sound from SX-150 and convert it to 6.3mm jack. and get the grand from it.
this picture displays full wirring. In this case, you need 4 pot controles. if you think that it's too much, then you can add mods.
1. The jumper at the 14pin of U1 will switch the LFO rate knob from hardwaired pot to MIDI cc stream. if your MIDI keyboard or sequencer can throw control change message 4C (76 in decimal) then it will change LFO rate.
then you don't need not only 10k pot but also R5, R4 and C2. it can make your borad more simple to build.
check the positions of R5, R4 and C2 by Components layout.
if you install Jumper at 14pin at U1 then you need to install R5, R4 and C2.
2. SX-150 have temperature drifts. so you may need tune each time when you play both pitch tune and scale tune.
as you know, "Tune" knob is for pitch. And "Span" means octave scales. If you think that you use SX-150 as FX sound only or you use it as synth percussion or so, and there is no need to get correct tune, then octave span pot may be no needed to tweak every time when you play. Then you can omit octave span pot and install trim pot on the board.
You can put this into any enclosure. This is the one of the fun of DIY, I think. I desgined the sticker as similar to left side of MINIMOOG. there is more pictures. Please check it.