Rongge

How make a Simple Siren with Four Transistors. This circuit requires only small 6V power from the speaker to generate sound two tones. Simple Siren with Four Transistors Circuit Diagram The circuit is more than simple. The first two transistors (left) are responsible for forming a flip-flop. This means that the 10K resistor will have a pulsed signal. The 4.7μF capacitor is charged and discharged in this signal are almost pulsating. Applied this to the oscillator (formed by the other two transistors) we obtain the desired sound output. The speaker can be any 8 ohm 1 watt the type used in portable radios.

This FM transmitter circuit uses four radio frequency stages: a VHF oscillator built around transistor BF494 (T1), a preamplifier built around transistor BF200 (T2), a driver built around transistor 2N2219 (T3) and a power amplifier built around transistor 2N3866 (T4). A condenser microphone is connected at the input of the oscillator. Working of the circuit is simple. When you speak near the microphone, frequency-modulated signals are obtained at the collector of oscillator transistor T1. The FM signals are amplified by the VHF preamplifier and the pre-driver stage. You can also use transistor 2N5109 in place of 2N2219. The preamplifier is a tuned class-A RF amplifier and the driver is a class-C amplifier. Signals are finally fed to the class-C RF power amplifier, which delivers RF power to a 50-ohm horizontal dipole or ground plane antenna. Use a heat-sink with transistor 2N3866 for heat dissipation. Carefully adjust trimmer VC1 connected across L1 to generate frequency within 88-108...