Language circuit controlled by phototransistor

Published:2012/8/19 22:50:00 Author:Ecco | Keyword: Language circuit , phototransistor | From:SeekIC

It consists of the light control switch and 35 voice IC. In the figure, photosensitive transistor VT1 and crystal transistor VT2, resistors R1 , R2, R3 and capacitors C1 , C2 , etc. constitute the light control switch circuit. Voice integrated circuit IC, transistor VT3 and resistors R4, R5 , etc. constitute a voice amplification circuit. Under the usual light source, VT1 showes a low resistance state, VT2 is in saturated conduction state, IC trigger side-pin 3 does not work without positive trigger pulse, then speaker keeps silent. When VT1 is obscured by the object, it will generate a negative pulse voltage which is coupled to VT2 base through C1, leading to VT2 into the cut-off state, then IC gets a positive trigger pulse to work, and the output audio signal is amplified through VT3 to promote the speaker emit sound.



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