- #1
powerlord
- 1
- 0
Sorry.. I know this is really simple..
I have 3 composite video signals, and switches to select between them.
The switches I have are SPCO, so I can't just use another pole for the switch voltage.
So, I need a way of detecting the video, and this switching on and LED.
At first I thought composite video was AC, so just made a transistor amp, decoupled the input.. but didn't work. Looking at the composite video on the scope I can see it is actually a DC voltage 0-0.5V... ah.
So.. I have a circuit where I feed the video in through a 1K resistor into the collector.
I have the LED and a 500R in series with the emitter (3904 transistor).
This 'works' in that it lights the LED when a video signal is present, but only weekly (3mA).
So, I need to increase the input voltage above 0.65 I suppose to bring it into saturation.
But how do I do that without effecting the video camera ?
I feel I need some sort of resistive voltage divider, but my attempts at building one alaways lead to the transistor being on all the time.. what am I doing wrong ?
I know I could add another transitor stage and that would do what I want, but I don't really want to do that :-(
I have 3 composite video signals, and switches to select between them.
The switches I have are SPCO, so I can't just use another pole for the switch voltage.
So, I need a way of detecting the video, and this switching on and LED.
At first I thought composite video was AC, so just made a transistor amp, decoupled the input.. but didn't work. Looking at the composite video on the scope I can see it is actually a DC voltage 0-0.5V... ah.
So.. I have a circuit where I feed the video in through a 1K resistor into the collector.
I have the LED and a 500R in series with the emitter (3904 transistor).
This 'works' in that it lights the LED when a video signal is present, but only weekly (3mA).
So, I need to increase the input voltage above 0.65 I suppose to bring it into saturation.
But how do I do that without effecting the video camera ?
I feel I need some sort of resistive voltage divider, but my attempts at building one alaways lead to the transistor being on all the time.. what am I doing wrong ?
I know I could add another transitor stage and that would do what I want, but I don't really want to do that :-(