Controlling 12V with 0.03V

Discussion in 'The Projects Forum' started by umibuta, Dec 4, 2010.

  1. umibuta

    Thread Starter New Member

    Dec 4, 2010
    8
    0
    Hi I am new to electronics and to this forum. I need some help with a electronics if someone can assist me.

    I am working on an external LCD monitor for a Video Camera. And I would like to use the signal from the Composite Video cable to power the LCD itself. Is there a way to use the 0.03V (30mV) to act as switch for the LCD monitor? I.e. When the video camera is switched on the LCD monitor is switched on as well. Also, as I am using the video signal to control the power will this interrupt the video signal itself to the LCD?

    I noted that the voltage from the video signal fluctuates from 0.02V ~ 1V. But when I switched off the camera as expected there is 0V. I have not knowledge on electronics whatsoever but I if given a circuit and parts I know how to source them and solder them :p

    Below is the simple layout.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    What you need is a "squelch circuit". The circuit monitors an audio, radio, or video line to keep downstream amplifiers turned off in the absence of a worthwhile signal.

    The circuit at the link is unbuffered (might load your video line) and uses obsolete op amps. Any modern op amp like the TL072 would substitute for the one in the schematic, but you may need a special buffer to take the video level off to the squelch without distorting the signal.

    The transistor with the open collector can switch a relay for power to the display.
     
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,766
    928
    am op amp with Jfet inputs would not load the line
     
  4. umibuta

    Thread Starter New Member

    Dec 4, 2010
    8
    0
    Thank you. I was just reading more about squelch circuit. Do I connect the squelch circuit directly from the RCA composite cable? I have modified the schematic as I have understood.
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    That looks about right. You can place a small relay (12 volt coil) between the 12 volt source and the transistor's open collector output. When the squelch is tripped by the video signal, the transistor will turn on and operate the relay. The relay will act as a switch for the 12 volts to the display.
     
Loading...