I've always been interested in high speed photography, and have decided to use my Arduino as a control system for taking high speed photographs.
My first effort is shooting pictures of a popping balloon popped by a blow dart.
The rig is mounted on a melamine board to keep everything organized. Each component is attached to the board. Most items are attached with velcro. I built a metal L that is attached to the back of the board and has a large number of female 1/8 inch 3-wire audio plugs on it and a couple of 1/8 inch 4-wire plugs. Each is meant to connect to a different device. Using plugs makes it easy to disconnect the setup and transport it.
I used an old Radio Shack electronics kit as the center of the system. It has 6 AA batteries in it that are tapped to provide 1.5, 3, 4.5, 6, 7.5, or 9 volts. It also has a number of pushbutton switches, LEDs, and other components, and a small breadboard. I use a larger breadboard for most of the wiring however.
Here is what the rig looks like:
And here is what the plugs on the back look like:
My system consists of a pre-trigger that extinguishes the room lights and opens the camera's shutter in bulb mode as the blow dart exits the straw used to launch it.
Then there is a vibration sensor near or attached to the ballon that triggers the flash, closes the shutter, and turns the room lights back on.
I found a circuit online that uses a pair of op-amps to create a high sensitivity vibration sensor using a piezo element: Internet of Things: High Sensitivity Vibration Sensor Using Arduino. (A company called HiViz also sells a simpler circuit based on a transistor.)
I adapted that circuit to use an SCR to trigger the flash directly, as well as notify the Arduino. I'm triggering the flash directly in order to catch the balloon as early in the pop as possible. If I used the Arduino to trigger the flash then the code to do so would add extra delay.
I built a photo gate trigger that detects the blow dart leaving the straw. It is a small block of wood with 2 holes drilled into it that cross at a 90 degree angle. I put a clear straw through one of the holes. I put an IR LED in one end of the other hole, and a high speed "optoschmitt" photo transistor circuit on the other side. I attached a threaded fitting to the bottom that attaches to the 1/4 inch stud on a tripod or lighting stand. The sensor looks like this:
The camera trigger has 2 parts: The shutter half-press, and the shutter trip. The half-press wakes the camera up, and can also trigger auto-focus. (For this application everything on the camera is in manual mode.)
There is a start button on the Arduino control panel that arms the system to take a photo. When you first arm it, it trips the flash to wake it up in case it was in standby mode, and also closes the shutter half-press switch for a few milliseconds to wake up the camera. While waiting for a trigger it closes the shutter half-press every 30 seconds to keep the camera awake.
I used 3 different LED lights to provide light for shooting. Two of them are from cheap LED flashlights: One is pointed at the balloon to help aim:
One held on a little tripod and points at the control panel.
The last is an LED closet light attached to the ceiling:
All 3 are powered by the 4.5 volt tap on the electronics kit. I connect all of them to the + terminal, and the cathode is wired to a MOSFET who's gate is controlled by the Arduino.
I use a Nikon SB-800 flash dialed back to 1/64 or 1/128 power to make it's duration as fast as possible.
Just this evening I got the first picture that I think is really worth showing off. Some of the others have been decent, but I really like this last image:
Even at 1/128, a xenon flash is too slow-discharging to get really sharp images of very fast subjects like popping balloons or bullets. What I really need is an air gap flash. Those are expensive however. I may yet break down and buy one...
