Trigger-to-Switch Project

Thomas Henry

Hello all,

Here's a handy thing to have around the music studio. It accepts a standard +5V, 5 mS trigger input and controls an isolated switch (relay, actually).

Here's why I built mine. My home studio (basement, if you want to get picky) includes a Boss-600 digital recorder and an old microcomputer running a DOS version of Cakewalk. The recorder has no MIDI provisions, but it does have a switch input. With a momentary, NC footswitch one can engage the playback, record punch-in, and several other things in the effects section. But like I say, it's not MIDI, whereas that's what Cakewalk spits out.

So, Cakewalk drives my own ADV-MIDI circuit, and the MIDI Start output of that (which is a +5V trigger) drives this new Trigger-to-Switch circuit, which in turns drives the Boss-600 recorder. Voila! I can now engage the recorder under MIDI control synchronized to whatever I've "recorded" in Cakewalk. It's like opening up a who gob of new tracks. I've been using the hell out of it to do all sorts of multitracking things.

For various practical reasons, I didn't want to employ CMOS switches or transistors. My main goal was to make sure the Boss-600 would be safe, and also didn't want to hack into my ADV-MIDI. So the circuit uses a simple relay and was built as a battery-powered standalone. This ensures that on the Boss side of things, it really is nothing more than a passive circuit (i.e., a switch only).

A note about the battery. There is no power switch. The unit only draws measurable current when engaged (at 5 mS, several times a week...let's see...). The rest of the time it sits idle. Current drain, then, is really no more than if the battery were sitting in the blister pack at the grocery store.

The relay is available from All Electronics, and everything else is common. I built the whole thing in a little project box (also from All). By the way, notice how the output jack is isolated. I used 1/4" jacks which had plastic shanks to keep the grounds from connecting via the front panel.

And, hey, I know this isn't sexy and I haven't invented relativity here. As you'll see, it's nothing more than a straightforward application of relays. I'm not claiming to have done anything extraordinary, so no snide comments about me being arrogant...I'm simply posting the stuff in case you'd like to use it, too.

Attached is the schem, PCB artwork, parts placement guide and photo.

You might wonder why I did a PCB for such a simple circuit. Well, when creating the PCB for the GM Voice at about the same time, I had a couple extra square inches left over on the PnP Blue layout, so I just snuck it in.

And where can you use the circuit, you might ask? Basically, anywhere a momentary NC switch is needed. This includes recorders, sustain pedals on keyboards, effects devices and probably more.

That's pretty much it. If there's any questions, post them here.

Thomas Henry

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Photo of my completed unit.

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Trigger-to-Switch.zip

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Zip file, containing schematic, PCB artwork and parts placement guide.

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crashlander42 · Joined: Oct 21, 2006 Posts: 292 Location: Orlando, FL (US)

Seems like a useful thing, but for some reason at the mere mention of the DOS version of cakewalk I started thrashing and foaming at the mouth like an epileptic in seizure. Must be some traumatic memory I'm repressing from my youth. Laughing

Thomas Henry · Posted: Sat Dec 08, 2007 9:39 pm Post subject:

Oh, yeah, before I bid adieu and close up shop, I should mention that this project isn't just for MIDI things. An analog synth keyboard can fire it, as can a sequencer, the SuperController (either the old one or the new-fangled one in the 21st Century), and who knows what else.

So keep your options open!

Thomas Henry

Usine Karate · Joined: Jun 09, 2007 Posts: 64 Location: Hackney Wick

Hi Thomas,

This looks pretty cool, I was wondering (not knowing a jot about relays!,
and being based in the UK) if this would work?
http://www.rapidonline.com/productinfo.aspx?tier1=Electronic+Components&tier2=Relays+%26+Solenoids&tier3=PCB+Relays&tier4=Microminiature+2A+DPDT+relay&moduleno=65078

hopefully so, although it does look alot more expensive!

Thanks

Usine

Thomas Henry · Posted: Sun Dec 09, 2007 1:57 pm Post subject:

Hi there.

Well, I'm pretty new to relays myself. But some nice people here on EM pointed me toward the relevant data I needed to come up with a reliable circuit.

You'll note on the schematic I have listed the characteristics of the relay (5V/130 ohms), and the currents through the coil and transistor (0.45 mA/45 ma). These are the figures you should watch when ordering a relay. I didn't see anything listed on the link you provided. But I feel certain you'll be able to find a cheap replacement elsewhere. This really is a garden variety part; there's nothing really special about it.

Good luck shopping!

Thomas Henry

Usine Karate · Joined: Jun 09, 2007 Posts: 64 Location: Hackney Wick

Thanks Thomas,

I think that one is 250 ohms, which is different to the specs you note. I have since found one matching from Banzai effects.

Thank you again for your help.

Usine

funkyfarm · Posted: Wed Jan 30, 2008 9:17 am Post subject:

This could be cool to control multiFX.

for example, DeltaLabs Effectron has a bypass input socket of this kind.
(this is what I call "dry loop")

through, I didn't understand if the switch stays closed during a Gate ON, or if the RC network at input descreases the incoming gate length...

a.b.o.z. · Posted: Thu Jan 31, 2008 3:07 am Post subject:

wow this is so cool. great for Boss DD-5 tap tempo.
What if trigger level is 10V?

STremclad · Joined: Jul 01, 2009 Posts: 32 Location: Canada

Fantastic, this'll resolve my sync issues with my Roland CR-5000! By ajusting it's tempo as close as possible I''ll be using this to restart the CR every 8 bars or so.

I was trying to design similar circuit when I found this thread.

Thanks Thomas!

STremclad · Joined: Jul 01, 2009 Posts: 32 Location: Canada

Well, I completed the circuit... Works fine. As for the CR-5000, well, it's more manageable with the start and stop input, the restart ain't as reliable when switched. This being said, I'd thought this type of relay would be ''quieter'', you can really hear the thing switch on and off, the click is pretty annoying, even with the headphones on... I'll need to find another way to get the CR in line (if anyone has a suggestion on this subject please let me know, I'd like to get around the Din Sync and use a 5V trig instead). Still happy I built this, a tape recorder should find it's way to my studio soon, this built will come in handy.

Thank's and Happy New Year!

Thomas_Henry · Posted: Sat Jan 01, 2011 8:54 pm Post subject:

Hi,

On my unit, the relay is very quiet. Without phones on, if I really listen I can just barely hear the contacts click on. As shown in the picture, mine is in an enclosure which probably muffles the sound somewhat. In any event, the click-clack is so soft that it would never pick up acoustically through a microphone. (The neighbor's barking dog is another matter.).

Glad you liked the project. This really was the key piece of apparatus in my home studio, simple as the project is. By the way, I'm still on the same battery!

Thomas Henry

STremclad · Joined: Jul 01, 2009 Posts: 32 Location: Canada

Hi Thomas,

Thank you for replying to my humble self!

I guess I was looking for trouble when fitting the board into an aluminium enclosure. I also used a different relay (a Songle SRC-05VDC-SH)... I'm sure I have a tube of epoxy somewhere, or some mineral wool... That will certainly solve my this issue.