The light turns on the siren. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Beginner radio amateur
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The light relay proposed by the German magazine "Funkamateur" is triggered when light hits the photoresistor R1 (see diagram) - this causes a loud siren sound.
Transistors VT1, VT2 are the equivalent of a unijunction transistor connected according to the sawtooth voltage generator circuit. The oscillator frequency is determined by the capacitance of the capacitor C1, the internal resistance of the photoresistor R1 and the resistor R2.
Transistors VT3, VT4, connected according to the Darlington circuit, perform the function of an AF amplifier. Replacement is possible. Photoresistor - any domestic; transistors: VT1 - KT3107, KT361, KT203; VT2, VT3 - KT315, KT312; VT4 - KT503, KT603, KT815 with any letter indices.
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