The flashing light doorbell not only has the sound of the doorbell, but also can emit flashing lights through the door lights at home. It is suitable for use in noisy indoor environments, and is also suitable for families with deaf-mute people.
1. Circuit working principle
The circuit principle is shown in Figure 30.
It consists of two parts: the basic doorbell circuit and the light and sound delay control circuit. Press the doorbell button SB, the TRIG terminal of IC1KD9300 music integrated circuit gets a high level, O/P outputs the music signal stored in the music integrated circuit, and after being amplified by the transistor VT 9013, the music is emitted from the speaker B. The amplifying circuit composed of the transistor VT1 inputs an amplified signal to the base of the transistor VT2 through the collector, and under the rectification of the diode VD1, the transistor VT2 is saturated and turned on. The light-emitting diode in the optocoupler IC2 emits bright light, which makes the low impedance between pin 4 and pin 5 of the optocoupler, making pin 4 of the IC3 555 time base circuit high, and the circuit of IC3 starts to turn on ( IC3 555 The time base circuit is connected as a low-frequency self-excited oscillation), and pin 3 outputs a low-frequency square wave pulse, which triggers the gate of the thyristor VT3 through R3, VT3 is turned on, and the door light starts to flash. When the music is finished, the speaker B stops sounding, and the transistors VT1 and VT2 are cut off, so that the pin 4 and pin 5 of the IC2 optical coupling circuit presents a high impedance, and the pin 4 of the IC3 555 time base circuit is at a low level, making the 555 The circuit is in a forced reset state, at this time pin 3 outputs a low level, the thyristor VT3 cuts off when the AC zero crosses, and the door light goes out. At this point the circuit is in the initial state of waiting for the button SB to be pressed next time.
2. Selection of components
555 integrated circuits use NE555, μA555, SL555 and other time-based integrated circuits; IC1 chooses ordinary doorbell chips such as KD9300; optocoupler chooses 4N25 optocoupler; β≥100 is required; RTX—1/4W type carbon film resistor can be used for resistor; MR100—8 type should be used for thyristor VT3; C4 uses ceramic capacitors; C3 and C5 use electrolytic capacitors; C6 uses CBB-400 polypropylene capacitors; VD1 uses IN4004 silicon rectifier diodes; VS uses 12V, 1W 2CW105 silicon voltage regulator diodes.
3. Manufacturing and debugging method
The circuit structure is simple and easy to use. As long as the welding is correct and the components are selected correctly, it can work normally.