Sound Amplitude Modulated Flashlight.

Even a flashlight can easily be adapted to send a sound amplitude modulated beam. The fidelity is not as crisp as that of the modulated LED or Laser because the incandescent filament in the light bulb has to change temperature at a rapid rate. The sound modulated flashlight works surprisingly well in spite of this.

A small Maglight is a very good choice to use since it can be focused into a tight beam and thus it will be easier to cover a greater distance.

To modulate a flashlight, you simply put an 8 ohm winding of an audio transformer in series with the batteries. The primary winding should be 1 or 2 K ohm and can be driven from an 8 ohm audio source. The source can be the earphone output of a small amplifier driven by a microphone or the earphone output of a small transistor radio.

The back end of the flashlight can be screwed off and the transformer connected between the end of the battery and the flashlight case. A plug, made by wrapping up some masking tape could be used to replace the original one. Two wires integrated into the tape plug can make the appropriate connections.

The receiver can simply be a photocell plugged into a small audio amplifier. Both are available at Radio Shack. They have a tiny palm sized audio amplifier. This type of amp could also also be used to drive the flashlight transmitter from a microphone.

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