Digital circuit production 04-sound and light alarm circuit

1. Circuit simulation and principle explanation

      This circuit is relatively simple, so the core is a multivibrator composed of NE555. Because what the multivibrator produces is really unstable, it is in a temporarily stable state, which is high and low for a while. In this way, the effect of cross-lighting of two rows of LEDs can be achieved.
      C2, R1, R4 and NE555 together form a multivibrator circuit. When first powered on, pins 2 and 6 of NE555 are in a low level state, pin 3 outputs a high level, LED1~3 does not light up, and LED5~7 lights up. The power supply continues to charge the C2 capacitor. When the voltage reaches 2/3 of the power supply, the output of pin 3 becomes low level, and the internal discharge tube of the 555 chip is turned on. When the C2 capacitor slowly discharges to 1/3 of the power supply, pin 3 becomes low again. From low level to high level. The circuit continues this process. By changing the resistance of the R4 potentiometer, the frequency of the buzzer sound and the speed of the LED light flashing can be changed.

2. Precautions

(1) When simulating, please switch to the simulation mode, and the device must be called in the simulation library;
(2) During the welding process, pay attention to the welding of polar devices to avoid damaging the device and affecting the circuit function;
(3) If you need to test the output waveform , you can disconnect R8 and R9 and the buzzer to make it cleaner~

3. Extended applications

     You can add a temperature sensor circuit on this basis to start alarming when the temperature reaches a certain degree Celsius; or add a human body pyroelectric sensor to start alarming when someone passes by, which is necessary to prevent thieves when you sleep at night; you can also design a small circuit in the front. The timing circuit functions as a small alarm clock~