Wiring an external tap tempo for m13

[jolly1423]

So I run my m13 and my dd-20 together and I have to set two tap tempo. I'd like to be able to run both off of one but the m13 doesn't have a tap output. I opened it p ant the tap switch is pretty simple, just 4 lugs, but I can find a schematic. I'd like to just 'piggyback' a mono jack to it but it also switches to tuner mode if you hold it down (although I NEVER use it's tuner). Do you think I can just experiment to i.d. the lugs or could I mass something up?

[Processaurus]

SPST momentary tact switches have 4 legs, usually 2 and 2 are connected together inside and are electrically interchangeable.  Just use the beeper on your multimeter and beep it out until you find a pair that beeps when you hold the switch down and doesn't when you let up.  Do it with the power off, of course  . 

About wiring your 1/4" jack, once you find the switch, find out with the beeper if one side is connected to ground, if so, make that the sleeve connection.  Basically you don't want to connect anything to the sleeve that wasn't already ground, because it will be shorted to the chassis ground.  Especially you don't want to short your V+ (probably +3.3v for the digital supply) to ground, if it turns out the switch is a connection between V+ and an input on a microprocessor.

If neither side of the switch is connected to ground inside the M13, you'd have to insulate the 1/4" jack from the M13 chassis and make sure the other, external switch box's chassis is also insulated (otherwise the metal boxes touching makes the unwanted connection).

In your external tap tempo box I would use one of the special DPDT momentary stompswitches like they sell at small bear, as two electrically separate SPST switches, one for the DD20 and one for the M13, and keep them totally isolated from each other, and use insulated jacks for the two connections, probably just leave the chassis floating (ungrounded).

[Hides-His-Eyes]

It is possible to do this with an arduino without modifying the M13 too.

A good start:

http://little-scale.blogspot.com/2008/05/how-to-deal-with-midi-clock-signals-in.html

More complicated though.

[jolly1423]

Hides-His-Eyes, Yeah, thanks but that's way over my head.

Processaurus , Why is it necessary to isolate the two pedals on the switch? I've built a lot of taps before and I've done a couple of duels for a dd-20 and a dd-5 and just piggybacked them on the small bear soft touch switch without any problems...

[Processaurus]

You don't want to combine two unknown circuits from two manufacturers.  While there is a chance it could work, it just as likely wouldn't, with another chance stuff could get wrecked on the M13, as you're running a part of the circuit out to the outside world that was not necessarily designed to be idiot-proof.

The boss stuff probably has all kinds of protection on the tap input jacks for abuse.