Sound Activated Flash
Today I took a dive into high-speed photography. My setup consists of a sound activated trigger, a disposable camera, and my Nikon D50. In a dark room, I set the camera exposure to bulb, then use the sound activated switch to trigger the flash on the disposable camera.
I was inspired by the work of Flickr photographer TurboJoe. Joe lives here in Greenville, and has taken some astounding photos of balloons popping, water dropping, and light bulbs bursting. He uses better flash equipment than I’ve got, and he’s much better at circuit design. I was after a quick, cheap method of getting this to work. Here are a couple of Joe’s shots…
Using Joe’s schematic, I set off looking for a silicon-controlled rectifier (SCR). This is the heart of the sound activated system, and can be connected to microphones, amplification, and other circuits. The output sends a signal to trigger the flash. Unfortunately, Radio Shack no longer carries such a beast. In fact, they are beginning to phase out their component parts, focusing strictly on gadgets and consumer electronics.
I wound up ordering a complete kit from HIVIZ for $18. This kit includes circuitry for the SCR system, a piezo element, and a time delay circuit. Both the SCR and time delay have potentiometers to regulate sound sensitivity and the length of delay. The whole thing comes with a solderless breadboard to make the connections. Since I’ve been somewhat incapacitated over the past two weekends, I used the time to put the circuits together.
The HIVIZ system comes with a cable that’s supposed to splice into the PC cable of an external flash unit. I don’t have an external flash, so I used instructions from MakeMagazine and cannibalized a cheap disposable camera from Walgreens. I removed the camera case and the film, then took out the flash and circuitry. I found two leads that are pressed together to fire the flash when the shutter release is depressed. To these, I soldered two wires and attached the other ends to a 1/8 inch phono receptacle. I also soldered an external battery case to the battery leads so that I wouldn’t have to open the case every time I needed to change batteries. I drilled a 1/4 hole in the back of the camera for the wires, then reassembled the case. By doing this, I had my flash in a stable box, I could change batteries easily, and I could press the recharge button for the flash that’s on the front of the camera. By adding the 1/8 plug, I could change trigger mechanisms for the flash without having to resolder everything. I also created a manual trigger with a 1/8 inch plug, wire, and a push button momentary switch.
When I finally got everything connected together, the time delay circuit just wouldn’t work. I bypassed it and went straight to the sound trigger, and got better results. I wasn’t able to adjust the sensitivity with the potentiometer like I had hoped, though. About the only sounds I could get to trigger the flash were sharp loud sounds, like a clap.
I was ready to start shooting. I set up a card table in our downstairs bathroom, then got my Nikon D50 and tripod. I positioned the sound trigger and flash, then focused my camera and set it to "bulb." My first target was one of my screwdrivers. I charged up the flash, turned off the light, then used my camera remote to open the Nikon’s shutter. I then struck the screwdriver against the table. The sound caused the disposable flash to fire, freezing the image. I did two of these – the original and one closer. In the images below, you can see the circular shock wave in the vinyl of the table covering…
Satisfied that the system was working, I was ready for balloons. I shot several of these, experimenting with balloon color, aperture size, and the angle of the flash. I found that a straight-on flash with the widest aperture turned out over-exposed. I angled the flash to the side and stopped down the aperture a bit, and the images seemed better. I’m sure I’ll have to tweek it a bit. Here are a few of the results…
Right about now I’m tired of balloons. I tried a couple of bouncing balls, but didn’t get good results. I’d love to do a firecracker, but I’m not going to set one off in our house. I’m either going to have to fix the trigger sensitivity, or think of something else that makes a loud sound and would have interesting visuals.
[tags]photography, high speed, sound activated, flash[/tags]