CORDLESS_HEADPHONES

Published:2009/7/14 11:21:00 Author:May | From:SeekIC

It is possible to use headphones with no direct connection to the audio source. This figure illustrates a simple transmitter circuit suitable for connecting to an audio source. Diodes D1 to D3 are three infrared LEDs in series, driven by TR2, an n-channel MOSFET with a drain-current rating of 500 mA maximum. The illumination of the LEDs is modulated by the audio signal applied, with TR1 current-limiting and shunting the bias of TR2 to ground when TR2 source current exceeds roughly 100 mA. Potentiometer VR1 should be adjusted for best results. A 9-V power supply is best used in this circuit because of the sustained level of current consumption. The transmitter range is about 1 to 2 m, but this can be extended by using reflectors behind the diodes.A suggested receiver circuit, using an infrared photodiode, D4, to detect the IR light, is shown in (b). The received signal is ac-coupled to TR3, another MOSFET. The output is taken from the drain terminal via capacitor C5. Bias can be adjusted with potentiometer VR2, and this circuit will run from a PP3-size battery. The circuit could be adapted for other applications.



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