Simple circuit, but I need help.

[klabtv]

I have (nearly) no clue what how to design this, but I need to build a very simple circuit. I want to build "tally" lights for some operator postions in my church's TV ministry. The light will illumiate when their graphics station (or such) is being used "on-line."

Our video switcher/mixer provides a circuit closure for each of the inputs...just for this purpose. I'm already using this with our cameras. The camera accepts the circuit closure and it causes the "camera control unit" to illumiate the tally lamp on the camera. The operator then can tell that they are being used "on-line."

I want to build a small box that contains the circuitry and a red LED for the tally for a graphics station. I figure I will have to feed it 12V in addition to the circuit that will be closed by my video switcher/mixer. I know this circuit will need a relay or transistor to accomplish the lighting of the LED, but that's all I know. I was hoping someone could give me specifics as to parts I need and so forth.

Thanks so much!

 

[Roff]

If the closure can handle 10 or 20mA, it could drive the LED directly. Otherwise, you will need a transistor and a few resistors. Do you have specs on the contact closure? I'm assuming it closes to ground. Do you know how much current and voltage it can handle?

 

[klabtv]

I will have to check on the closure specs... If I remember correctly, it is a very small amount of current at low (1.5 or 3 V) voltage. Yes, I believe it closes to ground. What resistors and transistor would I need? Also, I'm looking for a "bright" red LED that could be mounted in a small box enclosure. Any suggestions?

 

[Roff]

Most of the guys here have more experience with LEDs than I do. I was looking to buy some a few days ago, and all the high-brightness ones I found on Jameco had a very narrow beam width. Hopefully, someone can make some recommendations, so we both can get some.
We really need those specs before we recommend a circuit.

 

[Nigel Goodwin]

Most of the guys here have more experience with LEDs than I do. I was looking to buy some a few days ago, and all the high-brightness ones I found on Jameco had a very narrow beam width.

That's what makes them high brightness, they focus the amount of light in a narrower beam so it's brighter.

 

[Roff]

That's what makes them high brightness, they focus the amount of light in a narrower beam so it's brighter.

I understand that. I guess I just needed to do a more extensive search. Digikey sell some pretty bright LEDs with wide viewing angles.

 

[klabtv]

I gathered the manual for our video switcher and it says "The contact of each relay used to switch the current for the connected lamp allows a maximum of 200 mA/24 V switching." There are 16 pins (8 video inputs)...one that is the "tally output" and the other 8 are "internally connected to a common bus."

Does this make sense? As far as I know, the cameras that are currently connected aren't feeding voltage to the switcher...but I may be wrong.
Thanks again!