Writing on LEDs with a laser pointer

After [Ch00f] got his hands on an 8×8 LED display, he didn’t make a 64-pixel video game or VU meter. He made a laser doodler, allowing him to draw on this display with only a laser pointer.

Using LEDs as light sensors is nothing new; [Forrest Mims III] discovered that LEDs can also detect light way back in the late 60s. [Ch00f] played around with this concept before creating a circuit that uses an LED as both a light emitter and sensor that reacts to the ambient brightness.

[Ch00f]‘s laser doodler takes this phenomena and applies it to an Adafruit bicolor LED matrix. When a light shines on an individual pixel in the display, the ATMega48 senses the current and turns that pixel on. Since this these pixels have two colors, [Ch00f] used a latch circuit and a button to cycle between what color the ‘Mega writes to the display.

In the video after the break, [Ch00f] shows off his display by having the LEDs light up in response to a laser pointer. It may be a bit small, but we can see a lot of potential for something like this as a gigantic art installation.


  1. loathingkernel says:

    Very cool. And I think this hack can be used to even impress some chicks! Kudos dude.

  2. Robot says:

    Why not use different color laser to paint different color pixels ? I think there should be some sensitivity difference between different colored lights

  3. glamar says:

    So when will all LED screens become touch screen, by sensing no light where the finger is? … opps led screens only use LED for back light.

  4. Rob says:

    Love the creeper at the end.

    You know, I actually have a use for this project! Might play around with this.

  5. birdmun says:

    Rather than a button to select color, could you use a pulse modulated signal that the LED picks up to select the color?

  6. bzroom says:

    isn’t this a repost? the only addition being a button you hold down that changes color?




  7. greg says:

    Does anyone else see the optical illusion? Where the dots appear in the black space on the grid? Stare at it for a while.

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