Heat Detector and Siren Circuit Electronic.
Two transistors BC147 (T3) and BEL187 (T4) are joined in Darlington configuration to boost the sound from UM3561. Resistor R4 in series with a 3V zener is utilized to deliver the 3V supply to UM3561 when the relay is in activated state. LED1, joined in series with 68-ohm resistor R1 across resistor R4, glows once the siren/alarm is activated.
This schematic diagram come from circuit: Heat Detector + Siren
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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.