Looks like this is an extra device that I would put over the bi-color led and have it tell me what color it sees. This is an interesting option that might work. Is there any way of doing it without extra accessories? I hoping for a simple way to just read if the voltage is positive or not and go from there.0xFF wrote:You can use RGB light sensor, like this:
http://bradsrpi.blogspot.com/2013/05/tc ... ry-pi.html
I am just trying to have the raspi recognize if my tv is on or not. I figured the best way to do it is by wiring to the led that indicates if the TV is on or off. I wouldn't need the pi to recognize the negative value, just the positive. So if I can get it to recognize when the value is at the 1.84v that would be perfect because that would tell me the state of the tv.redhawk wrote:Where is the LED going to be used??
Detecting the flow of current would provide difficult on the Pi since the GPIO can only measure 0v to 3.3v it cannot measure negative voltages.
A solution would be to use 2 opto-couplers in parallel but have one with it's anode and cathode swapped to detect current going in the opposite direction.
Interfacing the Pi would then only require 2 GPIO input pins with 2 pull-up resistors from the 3.3v supply rail.
An alternative method would be to use a RGB light sensor as suggested by the previous poster but that would require an enclosed fixture to ensure no external light could penetrate and interfere with the light sensor.
This is a newish flatscreen tv. I was looking for a low power output that will tell me when the tv is on. I figured if it sends power to the led then I can use that as my source of power to tell me that its on. Its not really the LED that I am looking at, rather the voltages that it is outputting to that location during the on/off state.redhawk wrote:There are other ways to detect the presence of the TV I'm not sure if the LED would be a good method considering the need to enclose the light sensor.
Does your TV have any USB or Scart connector at the back??
Does it use the old (AM radio killer) CRT technology??
Use an opto isolator, then you can safely sense the presence of higher voltage supplies in the TV.krayzielilsmoki wrote:This LED situation may be too complex for what I need.
Here is a different scenario
If I can find another source of low voltage output while the tv is on, that will give me 0v when off, and a low voltage when on... how do I get the raspi to recognize that?