Circuit design of automobile oil level monitoring alarm

Car fuel tank fuel level detection is usually done by a level detector. When the fuel tank is full of fuel, the float boom rises, and the resistance of the potentiometer is adjusted to the minimum (some models also adjust the resistance of the potentiometer to the maximum), causing the fuel gauge (actually a milliamp The pointer of the gauge (meter) deflects to full scale; when the fuel level in the fuel tank drops, the resistance of the variable resistor is increased, the current flowing through the system loop will change accordingly, and the pointer reading of the fuel gauge also changes. become smaller. The automobile fuel level monitoring and alarm device introduced in this example can vividly and intuitively display the amount of fuel in the automobile fuel tank. It can also send out an audible and visual alarm when the oil level drops to a certain value to remind the driver to refuel in time.

How the circuit works

The automobile oil level monitoring alarm circuit is composed of an oil level monitoring circuit, an oil level display circuit, an oil shortage warning circuit and a power supply circuit, as shown in Figure 6-103.

The oil level monitoring circuit is composed of diode VD2, auxiliary potentiometer RP1 and float potentiometer RP2 in the automobile fuel tank. The oil level display circuit is composed of light-emitting diodes VL2~VL7, transistors V2~V7, etc. The oil shortage warning circuit is composed of diode VD3, transistor V1, light-emitting diode VL1, integrated circuit IC2, speaker BL and related resistor-capacitor components. The power circuit consists of diode VD1, three-terminal integrated voltage regulator IC1 and filter capacitors C1~C3. After the +12V voltage is stepped down by VD1 and stabilized by IC1, a +9V voltage is generated, which is supplied to circuits such as IC2 and V1~V7. When the car's fuel tank is full of fuel, the resistance of RP2 drops to the minimum value under the action of the buoy, causing V2 to V7 to conduct and the light-emitting diodes VL2 to VL7 to light up. When the amount of oil in the tank drops to half, the center head of RP2 slides to the middle position, causing V2~V4 to conduct, V5~V7 to cut off, VL2~VL4 still lights up, and VL5~VL7 goes out. When the oil level in the tank drops to the limit, the resistance of RP2 becomes the maximum value, and V2~V7 are all cut off. VL2~VL7 are all extinguished, causing V1 to be turned on. Pin 4 of IC2 changes from low level to high level. The multivibrator composed of IC2 and peripheral components oscillates (the operating frequency is about 10Hz) and works. Pin 3 of IC2 The pin intermittently outputs a high level, causing the light-emitting diode VL1 to flash, and the speaker BL to emit a "beep, beep" alarm sound. If only the yellow light-emitting diode VL2 is on, it means there will soon be a shortage of oil in the fuel tank.