SX-150 synth mod instructions, schematics and code
Many people have asked about the instructions and code for the SX-150 mod I did to add MIDI and Audio out, therefore I’m posting the plans for everyone to try. By using the Arduino as the brains of the operation, a lot of other options are available for the mod, really the sky is the limit. If you do any cool hacks to it, by all means, please let me know.
Parts List
- Gakken SX-150 Analog Synthesizer Kit
- Arduino (This one is the classic, but my favorite ones, are the ones from Modern Device)
- MCP4921 12-bit DAC
- 4N28 Optoisolator
- 1/4” Audio Jack
- DIN 5 Pin Chassis Socket (Female MIDI plug)
- Diode (N4148)
- Resistors(220 ohm, 100k ohm and 3.3k ohm)
- Wire, breadboard (or wherever you wanna do the circuit), soldering stuff and patience.
Connections from the synth
Back of SX-150
The contact spots shown on the picture refer to the connections on the schematic. Just make sure to get these ones right and that the soldering joints you make are pretty solid.
Casing
This part gives you a chance to be creative, so get your tools out and make something cool. For my mod, I used a cigar box, and made holes for all the cables that will get connected with the main circuit. I used epoxy to glue the gakken to the box and it is doing pretty well so far.
Just make sure that you will also be able to change the batteries when planning your holes.
Circuit Schematics
Schematics for the gakken sx-150 mod
NOTE: It was brought to my attention that the connections P1 and P2 on the Gakken SX-150 are reversed on the schematic above.
Arduino Code
Note that there is support on the code for a LED on digital pin 3 that flashes as notes are played. This has not been added on the schematics and it is optional.
If you improve the code, make some other cool mods or have questions, let me know!.
I’m now working on a standalone Arduino based MIDI sequencer on the cheap that can drive this little toy. Updates coming hopefully soon.
