Axoloti w/Teensy

[Mindsetup]

I read somewhere that it might prevent using teensy USB port after connecting to power. Can you still use the USB to upload code to teensy?

[mokomo]

if i recall correctly i had to snip away a tiny copper trace on the teensy to prevent USB power going into the teensy when USB is connected, so it would just draw from the axoloti 5v

[Mindsetup]

Thanks for the info!

[Mindsetup]

I was thinking how could I make this happen:
Connecting 4x4 led buttons to teensy to use as step sequencer. The leds would on/off when button is pushed. That is something I think I could do pretty easily.

But I would want the leds to be two color leds. Green led would light when pushing the buttons. Red color would show the sequence going forward the steps. How would I get the leds work like this?

Better to just connect the 4x4 to the axo and use the teensy for other inputs and Outputs? Or wire buttons and leds to teensy and just the red pin of the led to axo? Don't know if it's even possible to wire like that

[lokki]

you can send midi from the axo to the teensy to control the red leds.

[Mindsetup]

That's awesome! Any short instructions how to do that? Axo sends 5v midi? I have to convert it somehow?

[lokki]

well i guess there are several ways. either connect the teensy to the usb-host of the axo and send midi via usb (that will involve no additional hardware) or build a midi in circuit (optocoupler etc.) and connect the midi-din output to serial in of the teensy. software-wise (teensy side) i think it is compatible with arduino stuff, and you can just use the midi library which has many examples.

[Mindsetup]

Great info thanks a lot! I think I'm gonna have do the midi in circuit. I don't have any clue how to do that. But I sure will find out.

[lokki]

do you need the usb input on the teensy for anything else? the teensy can easily be made visible as a midi device.

[lokki]

and if you only connect the axo to the teensy you can also omit the midi in circuit and connect the two directly. there are some posts here on the forum about this as well.

[Mindsetup]

I don't think I need it for anything else, but I might need axo USB port.

[lokki]

i see. so yeah go with din-midi

[Mindsetup]

So I can connect midi from teensy to axo and from axo to teensy by wiring the right pins?

[lokki]

yes. usually you need a protection circuit on the midi in side, the optocoupler. but if you connect two micro controllers it should work without. if you encounter any problems later on, i.e. hum on the audio path you might need to add the opto. it also depends on the power you feed the axoloti and teensy.

[Mindsetup]

I'm feeding power to axo via micro USB. And I was thinking of wiring teensy to get power from axo. Is it OK to use the optocoupler in any case? Or is there a minus side to it? Do you know what kind of optocoupler do I need?

[lokki]

the opto is ok in any case. there are multiple schematics around for midi in, i.e. here for teensy:

https://www.pjrc.com/teensy/td_libs_MIDI.html

[Mindsetup]

Could I use this gpio method? Could it be easier?

Oops, this : http://community.axoloti.com/t/mongiloti-synth/1839/3

Using PA2 and PA3

"Hugo's patch example contained a great fix. Using the Midi IN objects from Hugo's patch, I connected my Teensy TX -> 220Ohm Resister -> PA3 on the Axo. Wallah, instant MIDI in without any interferance on the external socket. Niiice."

[lokki]

not sure what you mean by that, sorry.

[Mindsetup]

Whoops I forgot the link, edited

[lokki]

that is midi in to the axo. you wanted midi out to the midi in of the teensy, right?