I want to build a "switch indicator box" for our local church so that the speaker in the front has a controller that connects to an XLR connector so that when they want the audio man in the back to play music, they can press a button on their controller which will then turn on a red or green LED on a little box at the back of the church as a visual indicator to start the sound. I would like to have up to three switches on the controller that turn on their own LED on the box and maybe a power indicator led on that box.

For power, I would like to use a 120vac to 5vdc converter, if possible.

Has anybody done something like this that you can share with me?

Thanks

 

When you say XLR connector, do you mean that you'd like to use a standard microphone cable to send the information over?

 

When you say XLR connector, do you mean that you'd like to use a standard microphone cable to send the information over?

Exactly. I think it only has three "cables" through the harness, so I wasn't sure if I could have three switches or only two.

 

Hello,

You could use an variable voltage on the end (a voltage divider with a rotary switch) of the cable
and a voltage comparing chip like the LM3914 in the monitoring box.
This way you can have upto 10 leds.

Bertus

 

With an XLR you have 3 pins so you can only have 2 switches. With each switch/circuit sharing a common ground.
Of course you could go with a higher pin count XLR4,5 or 6.

Distance/voltage drop might be an issue at 5V. 12V might be a better solution.

 

Based on your description, it should be a straightforward task. You need one wire for each LED and one return wire. Thus, n wires can light up n-1 LEDs.

The key information you need to know is: a) the length of the wire run you'll use and b) the forward voltage of the LED, c) the current you'll run the LED at, and d) the DC voltage supply you'll use. Personally, I'd recommend using a 12 volt wall wart over a 5 volt one because this gives you more margin in case the wire length is long, meaning the wire's resistance is important in the circuit. You measure one of the wire's resistance. Then each LED is in series with two of those resistances. Add (the voltage drop of the LED) + (the current through the LED times twice the wire resistance) to get V0. Subtract this from the power supply voltage V and this can be used to figure the resistance of the resistor you must put in series with the LED by (V-V0)/i where i is the LED current in amps. Voltage must be measured in volts.

 

Based on your description, it should be a straightforward task. You need one wire for each LED and one return wire. Thus, n wires can light up n-1 LEDs.

The key information you need to know is: a) the length of the wire run you'll use and b) the forward voltage of the LED, c) the current you'll run the LED at, and d) the DC voltage supply you'll use. Personally, I'd recommend using a 12 volt wall wart over a 5 volt one because this gives you more margin in case the wire length is long, meaning the wire's resistance is important in the circuit. You measure one of the wire's resistance. Then each LED is in series with two of those resistances. Add (the voltage drop of the LED) + (the current through the LED times twice the wire resistance) to get V0. Subtract this from the power supply voltage V and this can be used to figure the resistance of the resistor you must put in series with the LED by (V-V0)/i where i is the LED current in amps. Voltage must be measured in volts.

The run is about 90 feet. However, I don't know about the resistance of the line yet.

 

With two signal wires plus a return you can get four different states or indications if you use binary. Would make the solution a bit more involved but a distinct possibility. Contact your local digital enthusiast for details.

 

Wow, if grades were being given for "Creative Over Complication 101" everyone would get an A+. Why over engineer a simple circuit? A 12V wall wart, 3 LEDs, 3 resistors (could use 1) and 3 pole (or more) rotary switch, and cable...done. The OP mentioned a XLR plug but that's only because he's familiar with them. It doesn't mean that's what he should use. If this cable is not going to be run in the open and will be permanent, CAT 5 is dirt cheap and will do just fine. For a 90 foot run I would not bother measuring the line resistance. It just isn't that critical to light a LED.
4 pin panel mount connector (Male)
http://www.radioshack.com/product/index.jsp?productId=2103996
4 pin plug (Female)
http://www.radioshack.com/product/index.jsp?productId=2103255
8 Pin Plug (Female)
http://www.radioshack.com/product/index.jsp?productId=2062445
They have the male panel mount for it too.

 

CAT 5 is dirt cheap ....

I agree with your comments but this one may depend on what the OP already has. If he has cable, female receptacles and a breakout box, that'd all work fine. If he needs the female parts, the XLR approach will cost more.

The XLR cable is 3 conductors and could be used to switch 3 LEDs. You don't need a ground loop. 3 toggle switches, wall wart and resistors as noted. Toggle switches to allow independent control of all 3. If they are not independent, for instance if you want just one at a time, then rotary is a good choice.

 

Here's a basic schematic. The speaker's panel has three toggle switches and three LEDs. The panel near the amplifier control has three LEDs and and the wall wart. I put an LED at each end so the speaker has a positive indication when each circuit is closed. The toggle switches can be replaced with a rotary switch if desired. The advantage of a rotary is that only one circuit will be closed per position but I'm not sure which scheme you want.

 

The XLR cable is 3 conductors and could be used to switch 3 LEDs.

Can't believe I wrote that. Mea culpa. It could be made true, but not for a simple circuit as we've described and CDRIVE has drawn, which nails it.

 

Can't believe I wrote that. Mea culpa. It could be made true, but not for a simple circuit as we've described and CDRIVE has drawn, which nails it.

Ha, when you wrote that I just presumed that the XLR's shell has a ground connection. I've only used them a couple of times so I didn't know for sure. If it does... you'd be vindicated!

 

I have to check but I'm not sure the "shell" has a ground connection. If it does, then I'm all set - no problems

However, if it doesn't and I'm stuck with only the two wires available (third for return), are you guys familiar with a way to use a voltage divider circuit like Bertus recommended earlier?

 

My understanding is that the shield and shell share a connection with one of the 3 conductors inside and one of the 3 connector pins. Or maybe there are only 2 conductors inside, plus the shield.

Choosing a solution gets back to the restrictions on acceptable solutions. Are you married to using a single mic cable? How about the 3 indicator lights (since 2 would appear to be dead easy, whereas 3 will be a bit more complex)? As we've seen, using an ethernet cable instead would give you all the conductors you need, with cheaper connectors on both ends. Are you ruling out that solution?

 

My understanding is that the shield and shell share a connection with one of the 3 conductors inside and one of the 3 connector pins. Or maybe there are only 2 conductors inside, plus the shield.

Choosing a solution gets back to the restrictions on acceptable solutions. Are you married to using a single mic cable? How about the 3 indicator lights (since 2 would appear to be dead easy, whereas 3 will be a bit more complex)? As we've seen, using an ethernet cable instead would give you all the conductors you need, with cheaper connectors on both ends. Are you ruling out that solution?

Unfortunately, I have to use the mic cable...The church has been wired with the cables dropping in different areas all going back to the sound board. So in order to not have to run another cable from the front to the back, I need to use this cable...

 

How about using a demultiplexor or decoder? The three wires can supply ground and two bits to select one of four outputs. The 74139 is a dual 2-4 decoder, and would fit the bill. A 74138 is overkill, but if available can be used in a pinch. I think this is what wmodavis is referring to.

 

In an XLR3 connector, pin 1 is grounded (common with the shell and cable shield) so the simplest setup would be two LEDs to indicate 4 states: all off, green on, red on, both on. The wiring and connections could be similar to CDRIVE's schematic but with only 2 hot lines. I would just use the switch to put 5V on the cable and do all the dropping resistor/LED stuff in each end box. By putting the LEDs in series as in CDRIVE's schematic, you may increase your cable losses enough to limit LED brightness with a 5V supply.

 

By putting the LEDs in series as in CDRIVE's schematic, you may increase your cable losses enough to limit LED brightness with a 5V supply.

Since 12V wall warts are far more abundant than 5V models I see no benefit to using 5V. Also keep in mind in mind that the lower the supply voltage the more extreme the effects of a few ohms of line resistance becomes. After all, that's why automobiles ditched the 6V system for the 12V system. It's also why our mains (USA) are 120V and not 12V.

 

Also keep in mind in mind that the lower the supply voltage the more extreme the effects of a few ohms of line resistance becomes.

I know, but the OP specified a preference for 5V and it's workable for his wire gauge and length so I worked within those parameters.

Small switch mode 5V supplies are even more abundant than 12V supplies now. They're called old cell phone chargers.