3v to contact closure, 3v to 5v

Forum 2005-2010 (read only) Hardware Interfacing
1

Hi all,

I have a video switcher that outputs a 3v signal for tally lights. I'd like to convert this 3v signal to a contact closure (for a device that won't accept voltage) and a 5v signal for LEDs, arduino, etc.

I suppose I could use relays, but I'm a little concerned about EMI getting back into the video hardware. Is there a simple circuit I could use with switching transistors? If I used two per tally light (one for CC, one for 5v) would I need to isolate them from each other, or could the 3v output power both without problems?

Thanks for the help ;D

2

Use a BC547, and put GND on input pin...

3

What a coincidence, I just ordered a few. Would a 2N2222 work as well, or should I stick with the BC547?

4

I think both have the same function.

5

The major difference between BC547 and 2N2222 is the current (I) they can handle... BC547 is rated for 500mA, 2N2222 800mA.

If you really need isolation, why don't you use an optocoupler (i.e. 4N25)? Something like this:

4N25
47R __ __ 10K
3V >-----///-----|o U |-- ------///-----< 5V
| | |
GND >----------------| |-------+----------------< Arduino pin
| |
--|_____|------------------------< GND

Video switcher side <|> Arduino side