This audio amplifier circuit is useful in classrooms to reduce the strain of lecturing ,if the surrounding environment is noisy. It uses the power amplifier IC LM380 that gives 2 watts output which is ...

The circuit in Figure 1 can help if you must transfer dc power and audio over a pair of copper wires. One application for such a circuit is a low-cost door-opening system with speech input. The ...

That outputs both the audio signal and a 40 kHz carrier signal, implemented using the Arduino ... circuit there is simple, consisting of the ultrasonic receiver, followed by a transistor amplifier ...