Using phototransistor to detect light changes on CRT display?

Discussion in 'The Projects Forum' started by Security101, Feb 21, 2009.

  1. Security101

    Thread Starter New Member

    Feb 21, 2009
    Hi Folks,

    Been a lurker but noob currently!

    I have a project i need some help with:

    I have a CRT computer monitor that displays an active screen that I need to have alert me when it changes. My thought is to use a phototransistor (or something else you might recommend) to detect the color change on the screen when an event has occured. This output would need to be a relay for other circuits (strobe/buzzer etc). The relay can trigger a larger relay for outside circuits if required.

    The circuit would need to be simple (as I'm old and lazy and cheap:D)

    Below is a picture of what the screen looks like. Assume it's like an excel sheet that auto updates every few seconds. The top "row" is the new activity.

    I want to direct the sensor at the top row in the blue area, and have relay closure when a red bar appears (primary goal) or a closure on any color change if needed or available.


    Once I have closure, I will be alerted and will reset the circuit (I can manage that part of the circuit;))

    I would appreciate any guidance on this!

  2. bertus


    Apr 5, 2008

    When you want to detect more colors, you must have more sensors with color filters.
    You have to look at what combinations of the sensors the relays must react.

  3. Security101

    Thread Starter New Member

    Feb 21, 2009
    Thanks for the advise so far guys!

    I like the idea af the TSL250R and it looks like it would work. What would I use to create the circuit?

    I'm not really concerned about the other colors just detecting between the static blue screen and the red bars is the most important.

  4. DickCappels


    Aug 21, 2008
    One more idea - use red and blue sensors and compare their outputs - this will improve reliable detection of red, particularly if the screen luminance or ambient light fluctuates.
  5. thatoneguy


    Feb 19, 2009
  6. kbirecki

    New Member

    Oct 22, 2009
    If this is an application you wrote, another way to possibly do something like this is outpulse a signal on the Serial port (there are at least two output lines you can use for simple on/off capability) and trigger a circuit to do something that way. This would be a very positive way to control it, and not dependent on color of the display. There is a simple MSCOMM control you could tie in to gain control over the serial port.