Sound and light alarm based on low frequency oscillator

Crystal oscillator

Quartz Oscillator 3225 20M OSC

An oscillator (English: oscillator) is an electronic circuit used to generate repeated electronic signals (usually sine or square waves). Low-frequency oscillators (LFOs) are used to generate frequencies from 0.1 Hz to 10 Hz. The oscillator of the alternating signal between Hertz. This term is usually used in audio synthesis to distinguish other audio oscillators. The oscillators can be divided into two main types: harmonic oscillators and relaxation oscillators. Oscillator).
Using cardboard instead of PCB board for electronic experiment production First, find a piece of cardboard of the right size, draw the electrical schematic diagram (or installation diagram) on it; then punch the hole on the cardboard corresponding to the position of the component on the diagram. The component is loaded into the corresponding position from the side of the cardboard that is not drawn with the circuit diagram; finally, according to the circuit principle, the component pins are connected by thin wires and soldered with an electric soldering iron, and then the power and output leads of the circuit are soldered well. Ok, after checking it, you can power up the experiment.
Circuit overview:
As shown in the figure below, it is an analog police car alarm sounder circuit. At the same time as the alarm sounds, the LEDs will also flash, which can be used for various alarms.
working principle:
The triodes BG1 and BG2 form a low frequency oscillator, and the output end is applied to the base of the BG3 tube through the capacitor C3 and the resistor R6. The BG3 and BG4 tubes form an audio oscillator, and the oscillation frequency is determined by the values ​​of R5 and C4, and Controlled by the output voltage of the low-frequency oscillator. When the BG2 tube is turned from off to off, the BG2 collector also changes from low level to high level. This positive pulse is applied to the base and emitter of the BG3 tube. Between, the positive bias of the BG3 tube is increased, and the frequency of the audio oscillation is increased. Conversely, when the BG2 tube is turned on by the cutoff, the positive bias of the BG3 tube is reduced, and the frequency of the audio oscillation is lowered. Therefore, the frequency is high or low. After the changed audio signal passes through the speaker, it can emit a continuous police car alarm sound.

Using cardboard instead of PCB board for electronic experiment production First, find a piece of cardboard of the right size, draw the electrical schematic diagram (or installation diagram) on it; then punch the hole on the cardboard corresponding to the position of the component on the diagram. The component is loaded into the corresponding position from the side of the cardboard that is not drawn with the circuit diagram; finally, according to the circuit principle, the component pins are connected by thin wires and soldered with an electric soldering iron, and then the power and output leads of the circuit are soldered well. Ok, after checking it, you can power up the experiment.