MCU-Based “PHOTO-PAL” Camera Controller

A while back, I designed a camera and flash control device that will be the subject of a future Circuit Cellar magazine article.  This device, which I affectionately call Photo-Pal, allows me to use sound (or a contact closure) to trigger a high-speed electronic flash after a user specified delay. The device consists of a microphone amplifier, a Microchip Technology PIC16F873A microcontroller, a 2 × 16 character LCD, and six pushbuttons for the user interface. Delay from sound trigger input to flash trigger output can be adjusted from 1 to 59,999 ms.

The Photo-Pal design (Source: R. Lord)

The high-speed photos are taken in complete darkness with the flash as the only light source for the photo.  The Photo-Pal device also controls the camera shutter. Once the room lights have been turned off, an “arm” push button input causes Photo-Pal to remotely press the camera shutter button, causing the camera shutter to open. The sound trigger input is also enabled. The triggering sound then starts a delay countdown, which then triggers the flash output. Once the flash has fired, the Photo-Pal then releases the camera shutter. 

For the last several months, I have been experimenting with using Photo-Pal to freeze the action of a light bulb being shattered by a hammer, water droplets rebounding from a surface, and eggs being shattered by a pellet from a BB gun.

The BB gun timing setup (Source: R. Lord)

 

For the photos using the BB gun to smash an egg, I needed to make a cradle to hold the gun so that each shot would be aimed at the same location. I also needed to establish how long it took for the pellet to reach the egg.

An egg hit by a BB (Source: R. Lord)

To make the measurement, I bolted three sheets of plastic together and drilled a large “target” hole. I then sandwiched two sheets of aluminum foil between the three sheets of plastic so that the two foil layers were separated. The microphone for the Photo-Pal was attached to the cradle so that it would be triggered when the BB gun was fired. My oscilloscope was triggered by the Photo-Pal flash output with delay set at 0, and the interval was measured between the time of the trigger output and the moment when the two sheets of aluminum foil were shorted together by the pellet passing through them. With the target set 4 feet from the muzzle of the BB gun, this time interval was measured to be 25 ms. For the egg photographs, I added another 20 ms to the delay so that the flash would catch the egg in mid-burst, after it had started to fly apart. The 45-ms delay was then programmed into Photo-Pal for the photos.

Egg smashed and sound-triggered flash (Source: R. Lord)

 

The Photo-Pal device has several other modes of operation where it can produce a burst of flash outputs for a stroboscopic effect, or can activate the camera’s shutter from sound or at periodic intervals for time lapse photographs. As you can see, the Photo-Pal device is a useful photography tool that also can be a lot of fun to play with.

Richard Lord holds a B.S. in Electrical Engineering and an M.S. in Biomedical Engineering. During his career, he has designed digital electronics for an aerospace company and several telecommunication test equipment manufacturers. Working as a consultant in the 1980s, Richard designed several medical pulmonary test instruments and the electronics for an autonomous underwater robot. His 2011 article “Panning Control: A Digital Indexing Panoramic Tripod Head” appeared in Circuit Cellar 248.

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