Every quarter midi note (software) to potential free contact GPO (hardware)

#1

Hi there - new to the Axoloti and new to the forum.

Could someone please shed some light on how to achieve the following:

Every quarter note, a potential free contact shall be switched for a few milliseconds.

Background: I'd like to "manually sync" the play/record/stop commands of several Digitech Jammans to midi clock. The electric path could be serial, something like
"tactswitch ==> potential free switch (Axoloti, potential free contact, pulsed every quarter note) ==> Jamman's footswitch contacts"

The Jamman receives its signal, when both the tactswitch and the Axoloti are switched. For live usage, you would keep the tactswitch pressed slightly before the next quarter note and - bang - the Jammans were exactly synced. This would be great.

Still have to find out, whether the Jamman's footswitch is normally open or normally closed.

So my questions are:
* Is this possible at all?
* Which Axoloti GPO would you use?
* I think, the output delivers +3.3 V (non-potential free). Could/would you apply a photomos-relais to translate the voltage into a potential free contact?
* What are the basic required patching objects?

Thanks in advance!

PS: If Axoloti could be a multitrack looper with track saving capabilities I would not think further about using the Jammans. ; )

#2

Its more a hardware question first... so Ive moved it there :smile:

the patching is relatively trivial , use midi/clock, if you search for 'clock' here you will get a lot of threads about this.

multitrack looper, from audio input...

would come down to memory limitations, there are some examples here of single track recording, so changing those to multiple is not an issue, if you are staying within a reasonable amount of SDRAM.
(43sec @ 32 bit)

streaming from the SD Card is supported by some objects but not writing to it... and Im not sure without a lot of work could be done efficiently = glitch free.

#3

Connecting to a footswitch input of external gear:

I suggest building a little circuit around a FOD817 optocoupler (or similar).
I have not verified this circuit, this is only a suggestion:

On the primary side:
GPIO to a 220ohm resistor to optocoupler anode, optocoupler cathode to axoloti ground.
On the secondary side:
footswitch jack ground to optocoupler emitter
footswitch jack tip to optocoupler collector
This assumes that the jamman has a pullup resistor on the jack tip internally.

Normally open or normally closed can be compensated with a logic/inv in the patch - but that does not change behavior when the patch is not running. Some gear auto-senses normally-open versus normally-closed when you power it on (assuming pedals are not pressed during powerup).

SDCard streaming recording, long time ago I did some tests, small buffer read performance is acceptable, but small buffer write performance can be really terrible. It depends a lot on the specific card, I've seen (a)periodic drops in speed that would result in dropouts unless the buffersize is increased. Increased buffersize conflicts with low-latency streaming playback if used simultaneously.

Recording loops into tables is more practical than streaming. 43 sec @ 32bit, but also 86 sec @ 16bit is viable. Copying the contents of a table (in sdram) onto sdcard (not streaming): the table/save object has known issues when using it for other than very short tables, will look into resolving that in the near future.