Com Cutoff Switch

[rochem]

I spent some time at a theatre today where a well-known lighting designer was teching through a show. However, this designer is also known for always forgetting to turn off his headset before shouting across the theatre to the stage/director/stage manager/other designers, etc. (anyone know who it is yet? ). I noticed that the Associate LD had rigged up a cutoff switch in a small box that he kept at his table and would push whenever the designer started to talk to others, to save the ears of everyone on com. I didn't get a chance to examine this closer, but I'd be really interested in rigging up one of my own.

Any thoughts on how I could do this? I'm assuming I'd want it in between the headset and the com station, so that you don't need a separate button for each channel. Also, the device should cut out the microphone, but leave the speaker connected. And finally, because this will often be used in a dark theatre, it would be great if an indicator light could be wired into the circuit, ideally pulling voltage from the com line (if it can be done without disrupting the signal, obviously), but I'm happy as long as I don't need to connect it to AC power.

Now that I think about it, it's possible such a product may already exist. However, I don't have as strong of a background in low-voltage wiring like this, and I think it'd actually be very educational (and cheaper) to try to build this myself. Thanks!

 

[derekleffew]

...(anyone know who it is yet? ). ...

Just about every LD I've ever worked with?


This "magic button" that the AssocLD used, did it turn off just the LD's mic, or everyone's? If the latter, Google "Clear-Com RMK-1".


RMK=Remote Mic Kill, a Clear-Com feature since the 500 series.

 

[rochem]

This "magic button" that the AssocLD used, did it turn off just the LD's mic, or everyone's?

Nope, just the LD's. It's independent of the clear-com station, so when you close the circuit again, you're still talking on all the same channels and whatnot. I honestly don't know where in the circuit this button landed, but I assume (based on my very limited knowledge of clear-com systems) that between the headset and the base station would be the most logical place. I got the impression that this was something he either built himself or asked someone else to build for him - he said that he never leaves home without it at the risk of incurring the wrath of the entire production team, and I'm not entirely sure if he was kidding or not.

 

[derekleffew]

Oh. Then could it have been a simple switch that opened pins 1, 2, or both, from the headset to the beltpack? A headset cough switch, as it were.

... The headset pin-out is as follows on most Telex and Clear-Com compatible headsets:
1 - Mic Ground
2 - Mic Positive
3 - Earpiece Ground
4 - Earpiece positive ...

 

[rochem]

Oh. Then could it have been a simple switch that opened pins 1, 2, or both, from the headset to the beltpack?

Yes, that's my assumption of how it probably worked. And while I've done a good amount of electrical wiring for straight 120V power, I'm not sure what components I would use to switch two pins in a four pin connector, or how I would wire in an indicator light of sorts without corrupting the audio signal. I mean, I guess I could just wire pins 1 and 2 to a switch then run 3 and 4 straight to the 4-pin thru, but will that work? And I have no idea how I could wire the indicator light in there.

Thanks!

 

[TheDonkey]

Oh. Then could it have been a simple switch that opened pins 1, 2, or both, from the headset to the beltpack?

It could also maybe have been a kill for the two/three XLR wires ( I don't remember how many coms use), so when he toggled the switch for a split second, the pack got reset and mic unlatched.

 

[ptero]

Yes, that's my assumption of how it probably worked. And while I've done a good amount of electrical wiring for straight 120V power, I'm not sure what components I would use to switch two pins in a four pin connector, or how I would wire in an indicator light of sorts without corrupting the audio signal. I mean, I guess I could just wire pins 1 and 2 to a switch then run 3 and 4 straight to the 4-pin thru, but will that work? And I have no idea how I could wire the indicator light in there.

Thanks!

You should be good to go wiring it this way. You could use a multi-pole switch and include an on board battery to drive an LED(s). Use red only for interrupted and battery life should not be too bad. Dunno about battery life if you add a green, for 'on', that would burn a lot.

Have you considered whether the button/switch would be momentary contact or on/off? I can see good and bad either way.

 

[rochem]

It could also maybe have been a kill for the two/three XLR wires ( I don't remember how many coms use), so when he toggled the switch for a split second, the pack got reset and mic unlatched.

I don't think so. The LD was using a remote station which had four separate channels of com, and the biggest advantage of this was that the microphone could be cut off with one master switch, then when the circuit was closed again, the mic would still be latched and talking on all the same channels, without needing to reselect channels. Unless I'm misunderstanding what you're saying.

 

[rochem]

You should be good to go wiring it this way. You could use a multi-pole switch and include an on board battery to drive an LED(s). Use red only for interrupted and battery life should not be too bad. Dunno about battery life if you add a green, for 'on', that would burn a lot.

Have you considered whether the button/switch would be momentary contact or on/off? I can see good and bad either way.

Yeah, that makes sense. I'm thinking a Double Pole Double Throw switch would work best, with pins 1 and 2 wired to one pole and the battery with LED wired to the other pole. I was just going to do a dim red light for when the com circuit was open, I don't see any need for a green indicator as well. I agree, I can see reasons for both, but I think having it be on/off would be best - just from the little bit I observed, there were a lot of times when the button would be off for more than 30 seconds at a time, and the LD used it when he walked away from his desk rather than having to move over to the remote station and unlatch up to four channels.

One more question - this system used a simple toggle switch, but the Associate LD said this didn't work very well. My ideal switch would be a square push-button switch around 1" square or larger, something that you can just reach over and quickly "slap" rather than needing to toggle something in one direction. I'd also love it if the button could be translucent with the indicator light mounted below it, the same way that the channel transmit buttons work on a clear-com master or remote station - albeit with the light indicating an open circuit rather than a closed one. Anyone have any good sources for switches (whether they match this idealized vision or not)? McMaster-Carr is the only large distributor that I've ever used for this kind of thing, but they don't seem to have any large push-button switches like this.

Thanks!!

 

[mstaylor]

You should be able to open a belt pack and see how the mic switch is wired. Basically you are just moving that switch off the belt pack to a table switch, as I understand what you are trying to do. The complication is adding the LED, but you have that solution.

 

[rochem]

You should be able to open a belt pack and see how the mic switch is wired. Basically you are just moving that switch off the belt pack to a table switch, as I understand what you are trying to do. The complication is adding the LED, but you have that solution.

Oh yeah, that's a really good point. I'll definitely do that, thanks! And if anyone has good sources for switches and other electrical components (other than McMaster-Carr), I'm open to suggestions!

 

[TheDonkey]

I don't think so. The LD was using a remote station which had four separate channels of com, and the biggest advantage of this was that the microphone could be cut off with one master switch, then when the circuit was closed again, the mic would still be latched and talking on all the same channels, without needing to reselect channels. Unless I'm misunderstanding what you're saying.

Ahh, ok, you're right.

I was thinking about our school system where we just run a single channel so relatching wouldn't be an issue.

 

[chausman]

Oh yeah, that's a really good point. I'll definitely do that, thanks! And if anyone has good sources for switches and other electrical components (other than McMaster-Carr), I'm open to suggestions!

Radio Shack? Amazon?

 

[derekleffew]

Mouser, Allied, Newark, Digi-Key, MCM Electronics, Fry's--all will likely have something suitable.

 

[epimetheus]

Yeah, that makes sense. I'm thinking a Double Pole Double Throw switch would work best, with pins 1 and 2 wired to one pole and the battery with LED wired to the other pole. I was just going to do a dim red light for when the com circuit was open, I don't see any need for a green indicator as well. I agree, I can see reasons for both, but I think having it be on/off would be best - just from the little bit I observed, there were a lot of times when the button would be off for more than 30 seconds at a time, and the LD used it when he walked away from his desk rather than having to move over to the remote station and unlatch up to four channels.

One more question - this system used a simple toggle switch, but the Associate LD said this didn't work very well. My ideal switch would be a square push-button switch around 1" square or larger, something that you can just reach over and quickly "slap" rather than needing to toggle something in one direction. I'd also love it if the button could be translucent with the indicator light mounted below it, the same way that the channel transmit buttons work on a clear-com master or remote station - albeit with the light indicating an open circuit rather than a closed one. Anyone have any good sources for switches (whether they match this idealized vision or not)? McMaster-Carr is the only large distributor that I've ever used for this kind of thing, but they don't seem to have any large push-button switches like this.

Thanks!!

You'll need a triple pole switch if you intend on breaking pin 1 and pin2 and have the led circuit. One pole interrupting pin 1, second pole pin 2, and third pole to switch the led. The alternative would be not to switch the mic ground, just the mic positive. Then you could do it with a 2 pole switch which will be much easier to find.

 

[nd925a]

Your autoparts store should carry 12 volt 10ish amp switches for car wiring that might work.

 

[gafftaper]

I love the idea of this project and am thinking about one of my own. If you do build one Michael, be sure to post some pictures of the results.

 

[Chris15]

I'd propose a different switching arrangement to that which has been discussed.
We have ALL heard a guitar or a phantom powered mic 'pop' when plugged in. You'd be doing the same if you switched by breaking the circuit.

A far quicker and easier solution is to take a series capacitor and a switch and short pins 1 & 2 in the headset feed.The cap deals with any DC that might be floating around to power an electret microphone but is basically a dead short to AC. So effectively you have clamped the output signal to 0v, ie. no sound...