FM transmitter Circuit with 4 Transistors
This circuit delivers an FM modulated signal having an output power of about 500mW. The input microphone pre-amplifier is designed close to a pair of 2N3904 transistors (Q1/Q2), and audio gain is restricted by the 5k preset trimmer potensiometer (trimpot).
Some substitutes for the 2N3904 are: NTE123AP, 2N4401, BC547 (watch lead orientation), and so on
In the electrical sector, a schematic diagram is usually used to describe the design or model of equipment. Schematic diagrams are usually utilized for the maintenance and repair of electronic and electromechanical devices / units. Original schematics were made by hand, using standardized templates or pre-printed adhesive symbols, but nowadays Electrical CAD computer software is often used.
In electronic design automation, until the 1980s schematics were virtually the only formal representation for circuits. More lately, using the progress of computer system technology, other representations were introduced and specialized computer languages were developed, because with the explosive development of the complexity of electronic circuits, classic schematics are getting less practical. As an example, hardware description languages are indispensable for contemporary digital circuit design.