Intercom light, LED for mount in XLR connector

[JonesH]

Hi!
I'm building an intercom snake (Making an intercom snake, what to include...) and am looking to make a red/greenlight system from mounting a LED in the cable mount of an XLR connector, thinking it should fit well there.

I was thinking that I could use a regular two-colored LED over a standard mic cable and by a two-way switch choose which legs to complete the circuit with, am I right?

I'll have access to ±15 V for the mic preamp circuit and from my rudimentary knowledge I could just slap a resistor between the legs of the resistor, right?

Sorry for noob questions.

[brianroth]

Dear Johannes,

What are your intended/expected goals with this system?

Bet,

Bri

[JonesH]

Originally Posted by brianroth

Dear Johannes,

What are your intended/expected goals with this system?

Bet,

Bri

Thanks for your reply,
My goal is for a small redlight/greenlight that can be used to tell conductors that the tape is rolling or cue announcers for instance. It should obviously be bright enough to be seen in daylight and I guess that it should also have a fairly wide visibility angle (don't know the exact english term).
If you have any suggestions, I'd be thankful.

[brianroth]

Dear Jonannes,

I read the link you posted, and now have a vague idea of what you want to accomplish.

I am assuming at the "stage end" you want to have a LED light up with either a green or red color (and perhaps NO color...as in the LED is not powered?).

Bi-color LEDs "light up" with a a particular color depending upon the direction of current/polarity of the voltage/current which is applied to the two pins of the LED. Since you said you have a +/- 15 VDC power supply available, that makes this project simple.

You only require TWO wires from the central control point: 0V/common/ground, and a control line.

The control wire is switched to either the + or - power supply, BUT you will require a single resistor "in series" with that switched line to avoid over-current into the bi-color LED. With +/- 15 supplies, I suggest a 1500 Ohm, 1/2 Watt resistor. That will provide approx. 10 mA of current into the LED, and the resistor will always "run cool", even if there is short circuit in the intercom wiring.

Best,

Bri

[JonesH]

Originally Posted by brianroth

Dear Jonannes,

I read the link you posted, and now have a vague idea of what you want to accomplish.

I am assuming at the "stage end" you want to have a LED light up with either a green or red color (and perhaps NO color...as in the LED is not powered?).

Bi-color LEDs "light up" with a a particular color depending upon the direction of current/polarity of the voltage/current which is applied to the two pins of the LED. Since you said you have a +/- 15 VDC power supply available, that makes this project simple.

You only require TWO wires from the central control point: 0V/common/ground, and a control line.

The control wire is switched to either the + or - power supply, BUT you will require a single resistor "in series" with that switched line to avoid over-current into the bi-color LED. With +/- 15 supplies, I suggest a 1500 Ohm, 1/2 Watt resistor. That will provide approx. 10 mA of current into the LED, and the resistor will always "run cool", even if there is short circuit in the intercom wiring.

Best,

Bri

Hi Brian,
Thanks for your reply.
I was previously looking at a three-legged LED with each connector to a pin on the XLR connector and using a switch to close either or none of the circuits. Do you think using a two-legged LED would be better somehow?

Also, the LEDs I've been looking at from swedish electronics retailer ELFA have 100/63 mCd or 40/25 mCd with 30 or 60 degrees viewing angle respectively. Do you think any of those might be suited for my application?

Thanks for your time and patience.

[Matt Syson]

Hi
The simplest circuit would probably use a 2 wire 'bi colour' LED.
However it would be a good idea to think of the 'best' way to wire it up as I presume you might use 1 cable from a multicore at some time so there is a possibility that a mic may accidentally get plugged in sometime.
I would therefore suggest having one 'side' of the LED to ground (pin 1) and the other using 2 resistors of say 500 Ohms to pins 2 and 3.
At the 'control' end the common (wiper) of the switch would use 2 resistors say 2K Ohms each, to go to pins 2 and 3 of the XLR. Ground on pin 1 of course. Now the 2 'on' contacts of your 3 way switch would go to +15 one way and -15 the other.
This would give you red/off/green signalling and in 2 of the positions would not damage microphones of any sort as it would 'appear' to be phantom power (at 15 Volts). When the switch is in the last position it would reverse the polarity so MAY upset mics that use phantom power, but would NOT upset normal Dynamic mics.
It would be possible to arrange a system that would use all the same polarity (positive) but this would get rather more complicated.
If you want green to be the 'normal' state of the indicator then wire it so that positive is usually on the cable. This would then not damage mics and allow you to check your 'LED' Plug is in the correct cable.
Matt S