Using this circuit diagram, can be made a very simple audio transmitter, using infrared connection.
The infrared emitter can be used to transmit an audio signal to some speakers, without using wires.
Three infrared LEDs (IR) are polarized with a current of rest by T1. This current level is set by P1. When applying an audio signal on the gate of T1, the current through the LED will be modulated. The light emitted by LEDs is also modulated in amplitude.
Maximum dissipation of 830 mW BS170 is at ambient temperature of 25 ° C, and maximum drain current is 500 mA. Therefore, even with the override FET, these limits are not exceeded.
Gate-source voltage of BS170 can be up to 15 V. If you have a signal source which provide a higher level, it is advisable to include a simple circuit protection (eg a 10 V Zener diode in parallel and a resistor in series with the input).
The optimal input for a working distance of several meters (1.2 2.4 m) is 100-200 mV.