This transmitter is modulates a infrared light source from an audio signal. Applications include a short range optical link for a microphone or other audio source. Range is up to 10 meters, but it can be increased with the aid of lens or other optical resources.
In the simulation a sine 1 kHz signal is applied and the waveshape in the output transistor is displayed in the virtual oscilloscope. Simulation is shown bellow. In a practical version you can use the BD136 as Q2 and BC548 as Q1.
To download the simulation files and Netlist - click here (ni0016.zip)