Oil level indication circuit made by light emitting diode

In view of the fact that early motorcycles did not have fuel indicators, we now introduce an oil level indicator assembled with light-emitting diodes, so that the rider can grasp the oil level in time. The indicator circuit is shown in the figure. LED1 is a red high-brightness light-emitting diode, LED2 is a green high-brightness light-emitting diode, VT1 and VT2 are 9013 imported triodes, RW is an oil level sensor, R1, R2, and R3 are 1/8 W, 1 kΩ resistors, and R4 is a 1/2 W, 200 Ω resistor.

The resistor Rl and the sensor form a voltage divider circuit. When the oil level is high, RW is almost zero. VA is far below 0.6 V, VT2 is cut off, and VT1 is turned on. The red LED of LED1 has no current and does not emit light. Only the green LED of LED2 emits light, indicating that the oil level is very high.

When the oil level drops, the RW value increases, and VA approaches 0.6 V, the conduction current of VT1 decreases, so that part of the current flows through the red diode of LED1. As RW gradually increases, the red light-emitting tube gradually turns brighter. At this time, the synthetic light gradually changes from green to apple green and orange. When the voltage drop of RW is greater than 0.65 V, the green diode goes out, and the red diode emits a pure red color, which means that the fuel is used up and refueling is needed.

The above sensor is for the TB50-B. If you use other models, you need to adjust the Rl resistance. The cost of the indicating part is less than 2 yuan, and the power consumption is less than 30 mA, which is less power than the pointer meter. The sensor current is 6 mA, which is safer.

If this circuit is used on the old Mulan (TB50-B) vehicle, it can reduce the trouble of changing the handlebar cover, changing the front fork or changing the handlebar. The indicator is installed in the original turn indicator, and the turn indicator can be replaced by a 6V buzzer. Other vehicles can also be tried.