Dang. [Mixtela] has just managed a seriously cool hack: running an entire MIDI synthesizer on an ATTiny85 to create what he claims is the worlds smallest MIDI synthesizer. That’s it on the left, next to a standard MIDI cable plug. 
The whole thing is so small it fits inside a MIDI plug and can run off the power supplied by the MIDI output, driving a small pizeo buzzer. Considering that the ATTiny85 has just 8Kb of memory and 512 bytes of RAM, this is no small feat (get it?). To create the sound, [Mixtela] simply drives the buzzer with PWMed square waves, creating the glorious early chiptunes sound that every retro gamer will recognize.
He even decided to implement some MIDI commands beyond just playing notes, including pitch bending, and is considering ways to add polyphony to his small miracle. Sure, it isn’t going to win any awards for sound quality, and without optoisolators it doesn’t really fit the MIDI spec. But it works, and remember that MIDI synthesizers used to be big, expensive devices that required a degree in sound engineering to program. Now, thanks to hackers like [Mixtela], you can build your own from parts that cost only a couple of dollars.
If it runs off battery, why would you need optical isolation?
It doesn’t. It runs off the power supplied by the MIDI port. IIRC the MIDI spec indicates that you can draw something like 200mA from it. I think it is known as phantom power or something. Also in the MIDI spec is that you need to put in optical isolation. I will agree that there is really no good reason to do so in this case. In fact it would be impossible to power it from MIDI if you did.
The MIDI specs have no such thing as phantom power. it has a 5mA max current loop so no 200mA
I stand corrected. Thought it was part of the spec.
The opto is to deal with ground loops. I think it is more important in longer cables or daisy chained devices
It’s not impossible.
He does it, I do it and Midi Solutions do it.
As long as the Power consumption stay below 5mA.
But you can’t power it without breaking the isolation.
The have to share a common ground and the opto isolator removes that common ground to avoid groud loops.
Yes you can.
Optically isolated power supply: LED and photocell :)
Technically you can use a DC/DC converter and still have isolation via the transformer but why would you bother – it’s not connected to anything else.
You can use an isolated DC/DC to isolate the power as well. Has little point if you have no other external interface of course.
You don’t in this case. Except that it’s in the MIDI spec, so this isn’t “really” MIDI. Although it totally is. If you get my drift.
I Think I already won the contest for the worlds smallest MIDI synth?
https://janostman.wordpress.com/2014/11/14/the-juno-synth-in-an-8-pin-dip/
That’s what I thought.
For me it seems that your chip is larger.. And this project is cool because it contains a speaker too :)
That is because the NXP LPC810 ARM doesnt exist in a SOIC-8 package so it have to be DIP-8. But I could claim the price for the worlds smallest drum synth which runs on a SOIC-8 ATtiny85? https://janostman.wordpress.com/2016/01/04/new-dem-video-for-the-dsp-d4-drum-chip/
If by smallest you mean breadboards and a mess-o-wires, then yes, you win!
https://janostman.wordpress.com/2014/08/07/the-entire-synth-inside-a-midi-plug/
And that is back in 2014.
Did you actually design that synth chip? There are no details in that link.
Yes, I did.
http://hackaday.com/2014/06/14/an-arm-based-dsp-modelling-synth/
https://janostman.wordpress.com/category/dsp-g1/
I meant the silicon level design but ARM synth design is equally impressive. Awesome
Great, now I want to build a modular synth again! I could get some mad polyphony out of a single card.
nice ! a little skimpy on the details though, and i’m sure you could get a lot more out of that ATTiny.
There’s a link on the linked page that gets you to all the gory details. Click one deeper!
thanks, i completely missed that link, very detailed description indeed. very nice
Here’s the link :
http://mitxela.com/projects/midi_on_the_attiny
Guy so should have played the super mario theme as a demo
GREAT!
How does this qualify as a synthesizer?
MIDI in -> sound out. That’s a synth.
Generating a tone through a piezio buzzer using a midi signal doesn’ t
Qualify a synth, a tone generator yes, synth no.
What’s your distinction between tone generator and sound synthesizer?
The earliest synthesizers didn’t do much more than a few simple tones either. The only difference was filters.
And attack and decayand sustain, release. Ring modulation and on and on
I considered a tone generator along the lines of an organ with very simple filtering and nothing else. Piezo oscillilator being controlled by a midi signal is a tone generator.
I don’t think you can draw a hard line, but it’s a bit like asking what’s the distinction between lasagna and a bowl of noodles, are they both “meals”?
@tom: “World’s smallest MIDI square-wave VCO with vibrato but no envelope generator” didn’t fit.