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.

13 thoughts on “Writing on LEDs with a laser pointer

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

    1. I actually tried doing this with a red laser. The problem is that green LEDs will pick up very little from a red laser, and I can’t use the red LEDs as sensors without another 8 I/O ports on the microcontroller.

    2. You are an impostor! There can only be one Robot.

      (Nice work Ch00f, I would love to see an entire wall of these.)

      – Robot

  2. 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.

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

    1. I think this will be quite hard to do because LED’s are already dynamically driven. So decoding any modulation will be tricky.

  4. 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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