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Simple circuits to permit a mixer to mute monitor speakers, light on-air sign?

R

radiofish

I would like to be able to interface some sort of a relay which mutes monitor speakers and activates an on-air light to the "mute" buttons on a Behringer mixer (1204 USB Pro). The mixer, a Behringer, will send the ALT 3/4 channel output to air and the main outputs to a production computer. The mute ALT 3/4 channel buttons conveniently light a bright orange LED on the mixer. Does anybody have suggestions on 1) how the mixer's mute buttons can be "tapped" to activate external relays that would control the monitor speakers and on-air light?

http://www.behringer.com/EN/Products/1204USB.aspx
Thanks.
 
If I remember correctly, there is a mute LED on the circuit board that follows the position of the mute button. Depending on your circuit design ability, you should be able to use this to drive the logic inputs of a Henry Engineering SuperRelay, or a similar home-brew version of the same circuit. One side of the LED probably goes to +12/15 volts via a dropping resistor and the other side goes to ground via a collector on a transistor. A voltmeter should be able to tell you what you have on the LED, along with looking at the general layout of the traces on the circuit board.

Provided the LED doesn't do something silly like blink (in the solo position), you should be able to do this. Personally, I would determine which side of the LED goes low when the mute button is engaged, then run this wire to a 1/8 mini headphone jack. Drill a small hole and mount the jack on the back of mixer. Space is generally pretty tight in those mixers, but it can be done. The Henry box has both an inverted logic input and an non-inverted input, so either way, with a little experimentation, you'll figure out which way turns on the relays when you want. If the board does have a solo position that makes the LED blink, you might want to modify the circuit so it is disabled.

The SuperRelay also has a handy 120 volt outlet on it that allows you to hang a blinking ON-AIR or RECORDING tally light outside the door.

If you want a circuit that can turn on and off a relay from this logic signal, it should be pretty easy to build. You can then control whatever size relay you want. I would take a transistor, like a 2N3904 to drive several 2 Amp DIP relays, then use the contacts on the relays to perform the speaker muting. I would be very careful building a tally light relay part, if you do build this. Make sure the circuit is fused and can't cross paths with any other signals in the box. Keep in mind that your circuit is not UL listed, so if it is built for a client, the safety of the circuit (and the liabilities of its use/misuse) are your responsibility. If they decide to run a toaster on the outlet and burn down the building, it is still your responsibility.
 
Jasonce66 said:
If I remember correctly, there is a mute LED on the circuit board that follows the position of the mute button. Depending on your circuit design ability, you should be able to use this to drive the logic inputs of a Henry Engineering SuperRelay, or a similar home-brew version of the same circuit. One side of the LED probably goes to +12/15 volts via a dropping resistor and the other side goes to ground via a collector on a transistor. A voltmeter should be able to tell you what you have on the LED, along with looking at the general layout of the traces on the circuit board.

Provided the LED doesn't do something silly like blink (in the solo position), you should be able to do this. Personally, I would determine which side of the LED goes low when the mute button is engaged, then run this wire to a 1/8 mini headphone jack. Drill a small hole and mount the jack on the back of mixer. Space is generally pretty tight in those mixers, but it can be done. The Henry box has both an inverted logic input and an non-inverted input, so either way, with a little experimentation, you'll figure out which way turns on the relays when you want. If the board does have a solo position that makes the LED blink, you might want to modify the circuit so it is disabled.

The SuperRelay also has a handy 120 volt outlet on it that allows you to hang a blinking ON-AIR or RECORDING tally light outside the door.

If you want a circuit that can turn on and off a relay from this logic signal, it should be pretty easy to build. You can then control whatever size relay you want. I would take a transistor, like a 2N3904 to drive several 2 Amp DIP relays, then use the contacts on the relays to perform the speaker muting. I would be very careful building a tally light relay part, if you do build this. Make sure the circuit is fused and can't cross paths with any other signals in the box. Keep in mind that your circuit is not UL listed, so if it is built for a client, the safety of the circuit (and the liabilities of its use/misuse) are your responsibility. If they decide to run a toaster on the outlet and burn down the building, it is still your responsibility.
Click to expand...

I would add that using an LED opto-isolator (optocoupler) is a great way to kill two birds: complete ohmic isolation and level translation. They're cheap and easy to deal with. Just parallel the mute LED inside the box with the LED in the optocoupler, and send the coupler's output to your external relay driver or whatever.

Kind Regards,
David
 
I would add that using an LED opto-isolator (optocoupler) is a great way to kill two birds: complete ohmic isolation and level translation. They're cheap and easy to deal with. Just parallel the mute LED inside the box with the LED in the optocoupler, and send the coupler's output to your external relay driver or whatever.

Kind Regards,
David


Good additional comments. I see many homebrewed circuits in which internal wiring is brought to the outside world without any thought whatsoever of isolation.
 
I agree with Reaves. Where the drive current was a concern, (Tlelkoor key phone system) I've also seriesed the LEDin an optocoupler. It keeps the outside world out of the box.
 
I agree, the opto isolation is an excellent idea. I've seen both methodologies implemented. If the relays are driven from a wall-wart style supply and the speakers and other equipment isolated by the relays themselves, this may be a bit overkill, but definitely worth the effort. Connecting the transistor side to your jack surely makes connecting any equipment to the optocoupler foolproof. May be worth at that point, isolating the shield side of the TRS jack as well, since we're going for isolation.

Consider if this were important, every serial and LPT port on a motherboard would be opto-isolated. Some of the spaces inside these style boards hardly have room for a jack, let alone an optocoupler, PC/perf boards and the like.

KISS principle...
 
Thanks for all of the GREAT suggestions. The Behringer 1204USB mixers seem to be a popular item and are very hard to aquire (back-ordered at BSW, not in Guitar Center stores, etc.). They have compression on each mic channel, 2 buses, orange LED lights when the mute buttons are depressed (live to output ALT 3/4), and USB in and out on the main channels. All for $160-$175.
 
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