Heating circuit of old BMW 740 rearview mirror

The reversing lens heating circuit includes four groups of circuits, which are connected as follows:

Constant current: one is positive and the other is negative, which can be connected to the positive and negative wiring of the nearest electrical appliance at constant current. If not, it needs to be connected from the power supply, and the negative wire can be grounded nearby; The control line, usually positive pole 12V, is connected from the positive pole of the reversing lamp, so that the rear-view image can be started when the reverse gear is engaged; The trigger line is the control line that enables the navigation LCD screen to automatically switch and display the signal input by AV (that is, the rear view image, which is not needed when reversing affects priority). This line comes from the rear-view camera and is connected to the corresponding connection port (image trigger) image signal line of navigation: the image signal of the camera is transmitted to the AV port of the navigation machine.

The heating function of reversing lens means that when the car is driving in rain, snow, fog and other weather, it can heat the rearview mirror through the electric heating wire embedded behind the lens to ensure the clarity of the lens surface.

The heating of car mirrors is generally suitable for rainy and snowy days. When the rearview mirror is heated, the heater behind the lens quickly heats the mirror surface, which can slowly remove the rain or fog on the mirror surface, saving the driver the trouble of frequently wiping the lens manually, thus reducing the danger of driving.

In fact, the working principle of electrically heated reversing lens is very simple and the cost is not very high. It is to install an electric heating sheet (electric heating film) in the lenses of the rearview mirrors on both sides. In rainy and snowy weather, when the owner turns on the electric heating function of the rearview mirror, the electric heater will quickly heat to a fixed temperature within a few minutes, generally between 35 and 60 degrees Celsius, thus achieving the effects of heating the lens, defogging and defrosting.