Hacking an LED light bar to bypass on off switch

Discussion in 'General Electronics Chat' started by CnnmnSchnpps, Jul 3, 2017.

  1. CnnmnSchnpps

    Thread Starter New Member

    Jul 3, 2017
    3
    0
    Dear AAC,

    Hoping to maybe find some tips on hacking an LED light bar. It comes with a built-in gesture switch (IR LED + IR receiver: place your hand in front to turn it on, kind of thing). The default position is "off", and it needs the gesture input to turn it on every time after receiving external power. Due to the location that I'm planning to mount it, I'd much rather have it just come on by default as soon as it receives external power (controlled via an external light switch).

    The PCB looks really simple, but it's beyond my abilities. I'm guessing the right side is the power electronics driving the LEDs, and the left side is the logic controller for the on/off mechanism. The white wires are the "in" from the power brick. The red/black wires are the "out" to the LEDs.

    On a wild hunch based on the only thing on here that looked like a transistor, I found that connecting V+ to the bottom contact of R7 triggers the on/off switch behavior.

    That's basically all the info I have. If anyone has any thoughts on how to force the LEDs to "on", would really appreciate your advice!!

    Photo 2017-07-03 22 40 30.jpg Photo 2017-07-03 22 40 51.jpg

    Cheers
    D
     
  2. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    7,832
    1,311
    I would bypass the transistor switch and see if it puts the positive supply or negative supply to the inverter chip IC3+ coil on the right side, and wire the dc supply direct to it,.

    then you can just put an ordinary switch on it or plug it in directly from the mains adaptor.
     
    CnnmnSchnpps likes this.
  3. CnnmnSchnpps

    Thread Starter New Member

    Jul 3, 2017
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    0
    Hey thanks so much for the response! Sorry but any way you could dumb it down for me a little more? I do have a multimeter but what leads should I measure? And where to actually wire in the dc supply?
     
  4. BobTPH

    Senior Member

    Jun 5, 2013
    1,540
    365
    D1 and V1 are the IR emitter and sensor. If you are lucky, it might just be looking for a reflection from one to the other and nothing more. If so, a piece of white paper over the top of both of them might cause it to turn on right away.

    Bob
     
  5. CnnmnSchnpps

    Thread Starter New Member

    Jul 3, 2017
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    You are right. Unfortunately the behavior is that a reflection will make it flip between on and off modes. So something permanently in front of the sensor doesnt help :(
     
  6. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    7,832
    1,311
    You need a dvm to check which supply the transistor is switching to the IC3 chip, then bypass it.
     
    Last edited: Jul 3, 2017
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