Haunting season is upon us (yes, I know it’s only September), and you’re probably thinking about all the props and effects you want to build for your haunted house.  Video effects are becoming more popular, but in most instances they’re no substitute for good old-fashioned physical effects.  I say “why not have both?”  Give your videos the power to affect and control the real world!



Yes, it’s a trick.  No, there was no fancy video editing involved; the trick looked exactly the same to the people standing in the room with it.  Here’s the behind-the-scenes video showing how it was done:



As you can see, there’s an air hose taped to the back of the monitor that did the actual blowing.  You’re not limited to just blowing out candles, though.  Any physical effect you can control with electricity can be synchronized to a video.  This includes lights, motors, pneumatic cylinders, other video players,  solenoids, etc. The secret is using DTMF tones (yes, like the beeps your phone makes).

Most video players have at least 2 audio tracks.  When you edit your video, you can keep one track for the audio that goes along with your video (in this case it was the blowing sound).  In the other track, place appropriate DTMF tones where you want your effect to turn on and off.

Next, you’ll need a DTMF relay board to decode the tones and switch things on and off.  In the videos above, the video was being played in a standard DVD player, and one of the 2 audio outputs was connected to the DTMF board.  When the girl in the video started blowing, the board received an “on” tone and turned on a relay.  This closed the circuit powering the air valve and out went the candle.  When it was time to stop blowing, the DVD player sent the DTMF board an “off” tone, the relay opened and the air valve shut off.

You can use this trick to synchronize all kinds of things:

  • Turn on a light when a video character lights a match
  • Fire a strobe right before a thunder sound
  • Activate a water sprayer right when your video person sneezes
  • Shoot a puff of fog when something magical happens on screen

The possibilities are endless once you realize that the video world and the physical world don’t have to be separate things.

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