The following is adapted from a Fort Awesome blog post in 2012.

I recently had a discussion with another photographer about taking photos of fruit dropped into water in a wine glass. He had tried it but ran into the problem of getting the timing right. Basically, he dropped the fruit and tried to guess the right time to take the picture. While he go some good shots, there were a lot pictures where the timing was wrong. This got me thinking, there had to be a better way. I decided to build a shutter release that would take a photo after an IR beam had been interrupted.

The first thing I needed to do was figure out how the shutter release for Sony Alpha cameras works. I bought an extra remote shutter release:

Then I took it apart. After examining how the mechanism worked and a little investigation with a multimeter, I determined that red was the common ground and that shorting yellow to red engaged the auto focus and shorting all three took a picture.

My first goal was to build a circuit that would take a picture immediately after the beam was broken. I used a paired IR LED and IR photodetector to create the beam. The output of that was inverted and used to control two NPN MOSFET transistors that would connect the yellow and white shutter release wires to ground.

With that complete, I decided to add a variable delay into the circuit. This would allow me to choose the delay of the circuit based on how high was dropping the object from instead of forcing the height based on the delay in the circuit. To implement this I used two 555 timer chips (actually, one 556 timer) in series. The first stage implements the variable delay and the second stage ensures the release is triggered long enough for the picture to be taken. I didn't know how long the trigger spike needed to be so I decided to play it safe and simulate someone holding the trigger for a fraction of a second.

When the output of the photo detector goes low it will cause a small low pulse on the trigger pin of the first stage. This will cause the output of the first stage to go high for a variable length of time. Which we can calculate with the following:

t = 1.1 * R * C

R is between 0 and 5 MOhms. For 90 nF this gives us a range of 0 to .495 seconds.

When the output of this stage goes low again it will cause a small low pulse in the trigger pin of the second stage. This will cause the output of the second stage to go high for .517 seconds (1.1 * 1 uF * 470 kOhms). While the output of the second stage is high all of the camera wires will be shorted to ground and a picture will be taken.

After attaching the IR LED and IR photo dector to wires and jerry rigging a platform to hold them in place, I started taking pictures. Initially the timing wasn't quite right.

But I was easily able to dial in the correct delay. Unlike the guessing method, almost every shot was correctly timed. Unless, of course, I missed the glass or hit the lip.

Now that the triggering problem is solved I will be able to quickly modify lighting, fruit, liquid, drop height, etc. to get the exact look I want.