Tag Archives: optointerrupter

Catching drops of water with an ATmega48P

Drops of water are often captured in perfectly timed photographs with the help of an optointerrupter, light source and air gap flash.

As HackADay’s James Hobson notes, this configuration is typically expensive or difficult to put together.

Fortunately, a Maker by the name of Michal has come up with a viable alternative using an array of LEDs to illuminate the drops.

“He [uses] a IR diode, a photo-resistor, a few spacers, some plastic and a bunch of hot glue to make up his optointerrupter. When the droplet passes through the IR beam it breaks the signal from the photo-resistor which then triggers his Atmel ATmega48P [MCU],” says Hobson.

“It waits 80 milliseconds and then turns on the LEDs for approximately 50¬†microseconds. Meanwhile, [the Canon] camera is watching the whole event with a shutter-speed of a few seconds.”

As Michal explains in a detailed blog post, one of the nice things about using an LED configuration is that it boasts rise and fall times considerably shorter than traditional camera flash, which lights up for approximately 1-2 milliseconds, rather than 50 microseconds.

“That’s why most of the motion-stopping photography relies on more exotic air-gap flash units,” Michal concludes.

Interested in learning more? You can check out the project’s official page here.