Car oil level monitoring alarm circuit design_alarm circuit diagram explanation

　　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.

　　The automobile engine tachometer introduced in this example is made of single-junction transistors and integrated operational amplifiers as main components.

　　Circuit working principle: The automobile engine tachometer circuit consists of a relaxation oscillator, a differential circuit, a comparison amplifier and an ammeter drive circuit, as shown in the figure.

　　The relaxation oscillator circuit is composed of resistors rl-r3, capacitor cl and single-junction transistor vu.

　　The differential circuit consists of capacitor c3 and resistors r4 and r5.

　　The comparison amplifier circuit is composed of an operational amplifier integrated circuit lc, resistors r6-rlo, capacitor c2, and diodes vdl-vd3.

　　The ammeter driving circuit is an electronic switching circuit composed of resistors rll-rl3, capacitor c4, potentiometer rp, thermistor rt, Zener diode vs and transistor v.

　　The pulse frequency signal obtained from the breaker contact s of the distributor controls the working state of the relaxation oscillator and the comparison amplifier. When the breaker contact s is turned on, the relaxation oscillator does not oscillate, ic outputs low level, v is in a cut-off state, and no current flows through the ammeter pa; when the breaker contact s is turned off, the relaxation oscillator oscillates Work, the generated oscillation signal is differentially processed by c3 and r5, and then added to the positive input terminal of ic through vdl, r6 and vd3, so that lc outputs a high level, v is turned on, and +l2v passes through the c and e poles of v and rp are added to the ammeter pa (the average current flowing through pa is proportional to the pulse frequency generated by the breaker contact s); the engine speed is indicated by the ammeter pa.

　　Component selection

　　rl-r13 all use 1/4w metal film resistors. rp chooses multi-turn potentiometer or synthetic membrane potentiometer. rt uses a negative temperature coefficient thermistor. cl-c3 uses monolithic capacitors or polyester capacitors; c4 uses cbb capacitors. vdl-vd3 all use 1n4148 silicon switching diodes. vs uses 1/2w, 5·6v silicon zener diode. vSelect s8050 silicon npn transistor. vu uses btt3 type single-junction transistor. IC uses LM339 operational amplifier integrated circuit. PA chooses lma ammeter.