Light control alarm circuit diagram test with Multisim Simuate Software

The picture above is a simple light control alarm circuit, so we analyze, a taste of wonderful electronic technology. First of all, we see the circuit in the right light resistance R and transistor VT1 and VT2, and the buzzer HA, then we can probably guess its working principle is because of R resistance changes, R resistance changes in voltage across the transistor led to changes in state , Thus affecting the working status of the buzzer. In multisim simulation software to build the following circuit diagram, which is a resistor divider circuit, the greater the resistance of the photosensitive resistor, then the higher the voltage across it.

Light control alarm circuit is the key components of the transistor, the composition of the transistor we find Qin has Huang's teaching materials. In general, no matter NPN type or PNP type transistor, there are B pin, C pin and E pin. Just like when it comes to diodes that are reminiscent of one-way continuity, when it comes to transistors, you have to think of "current amplification," and we analogize transistors with real-life faucets (B is a valve, C is a water tank and E is a water pipe) It is easy to understand. To NPN transistor, for example, when the voltage between the BE reaches the trigger voltage (0.7V) is equivalent to the faucet valve is open, then the water in the tank can flow to the water pipe, the specific flow and the degree of opening of the valve, which is the role of the transistor Enlarge the area; when the valve is opened to the maximum degree, the flow of water in the water tank to the water pipe is fixed at this moment, that is, the triode acts on the conducting area; of course, there is no water flow when the valve is closed, that is, the triode acts on the cutoff area.

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Back to the original light control alarm circuit, when the photosensitive resistor increases to a certain value, the transistor VT1 conduction (Note that conduction here is different from the transistor "on" term, just to illustrate this When the transistor to open the same faucet valve, there is water flow only, the following VT2 is the case), then VT1 collector current flows to the emitter, which means that at this time base transistor VT2 current flows at the same time produce pressure Drop; if the transistor VT2 conduction, then the buzzer will make a sound. Schematic diagram built by multisim software as follows, when we adjust the R3 (photoresistor) resistance to 40K, transistor Q2 base voltage of 0.75V, the buzzer beeps sound.![Screenshot_11.png]

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