So I have had an electronics hobby for awhile, making various things with Arduino, sometimes related to music gear. I decided to take up the challenge of a CV to MIDI converter because I have plenty of parts laying around, and can always use an excuse to buy what… $15 in electronics? I am using a Pro Micro board, which can use the MIDIUSB library (though not as host, which is fine – we do not want that here).
I followed the MCP600x input style recommended all over the place for eurorack format which buffers the input to not exceed a certain voltage. We don’t want to fry the 'duino… MutableInstruments are kind enough to have provided this for everyone and so I followed their Grids inputs pattern.
Though I’ve never done this before, I took an opportunity to learn about inverting voltage using an op-amp, and put a TL072 to work following this stackexchange thread.
Vin is regulated through a 7805, and the negative voltage supplied to the TL072 can come right from the -12v eurorack rail.
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I should add that I’ve been doing the hardware design work in Eagle as well, and intend to put all of this in a Github repository at some point soon. It’s very spare time for me, but it’s a simple Arduino application… for now. Given that though, I really do want some level of polish.
I will be wanting to add buttons with rgb leds, similar to the Hypno buttons, one per socket, to affect the page. This way we will have access to all the parameters. Well, 8 at a time anyhow. I am also contemplating attenuators (or attenuverters?) per input… at least for my current application that would mean one less module to consider space for on my tiny 42hp palette.
What is the RGB button part number used by the Hypno? I have seen several that I could use, but as with the MutableInstrument inputs it’s nice to re-use what others have proven to work well. 
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Glad you’re getting into some hardware dev, looks like you’re learning some good stuff!
Hypno actually uses the same buttons/caps as MI gear (its in stages/marbles/plaits and others).
The button is not RGB, its a simple switch, the rgb led is a separate LED. The part number doesn’t matter much since its just peeking through a window on the panel tbh but I can recommend you actually upgrade from the Hypno part to WS2812B smart LEDs (also called neopixels by adafruit) since they are very easy to rig up (with adafruit’s libraries/guides) and don’t require much extra circuitry to get running.
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Nice, understand regarding the switch and LED configuration. I have used the 2-wire LEDs before – that will be excellent as far as pin usage on the Pro Micro. Thanks for the thoughts Ron!
