eli5 what is this iconic high pitched sound you hear, when a movie or game character activates night vision goggles? Is this a real thing?
In: Technology
The singing is from the charging coil being pumped. Old night vision used a photo sensitive vacuum tube that required a lot of dc voltage but not much current. Driving a step up transformer was the way to do this. But transformers only work with ac and batteries are dc. So an oscillator circuit generates a small ac wave from the batteries and that wave is fed to the transformer. High voltage from the transformer is sent to a rectifier and a very high voltage capacitor. Typically the result was around 20000 volts.
The singing sound is the magnetic field of the transformer making the transformer core vibrate. As the high voltage cap becomes charged the current in the transformer shrinks in the same way a ball bounces as it drops energy. (It is called a sync function.)
The end result was to put this high voltage tube up against your eye ball and go “ooo, look at that”.
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