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Ding-dong electronic doorbell

2014-11-11 00:36  
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Ding-dong electronic doorbell
The ding-dong electronic doorbell circuit is composed of the power supply circuit, trigger control circuit, audio oscillator output circuit, and it is shown in Figure 3-125. Power supply circuit is composed of the power transformer T, rectifier diodes VDl-VD4 and filter capacitor Cl. Trigger control circuit is composed of the doorbell button, control circuit S, diode VD5, capacitor C2 and resistors Rl, R2. Audio oscillator A consists of the Dl, D2 which are inside of four NAND gate IC (Dl-D4) and resistor R3, capacitor C3. Audio oscillator B consists of the D3, D4 which are inside of IC and potentiometer RP, capacitor C4. Audio output circuit consists of resistors R4, R5, diodes VD6, VD7, transistor V, and the speaker BL.