Design and manufacture a brake light delay extinguishing circuit

When the vehicle brakes, the driver presses the brake switch, and the brake light lights up immediately. After releasing the brake switch, the brake light goes out immediately. If the brake light can be delayed for a period of time and then turned off after releasing the brake switch, it can better alert the following vehicles to pay attention. The circuit shown in the figure is a brake light delay turning off circuit, and its working principle is as follows:

Integrated circuit CJ0311 is a voltage comparator, with pin 6 as its control terminal. When pin 6 is at a high level, the state of the output terminal is determined by the input voltage of its "+" and "-" input terminals. If the voltage of the "+" terminal is higher than the voltage of the "-" terminal, the output is a high level, otherwise the output is a low level.

When its ⑥ pin is at a low level, CJ0311 is forced to reset and its output terminal outputs a low level.

Switch K2 is the control switch for whether the brake light is delayed to turn off. When switch K2 is in the disconnected state, the ⑥ pin of CJ0311 is low level, its output terminal outputs low level, transistor T is cut off, relay J does not work, its contact JK is disconnected, and the brake light L is not on. When the brake switch K1 is stepped on and closed, +12V electricity lights the brake light through diode D3, and the brake light does not turn off with delay, that is, the brake light goes out immediately when the brake switch is released. When switch K2 is closed, because the brake switch K1 is always in the disconnected state when the vehicle is running normally, the "+" input terminal of the voltage comparator CJ031 is low potential, and its "-" input terminal has a 6V voltage, so its output terminal outputs low voltage, transistor T is cut off, relay J does not work, and the brake light is not on. When the vehicle brakes, K1 is closed, and the +12V voltage lights up the brake light L through the diode D3, while charging the capacitor C through the resistor R4 and the diode D2. Since the resistance of the resistor R4 is very small, the capacitor C is quickly filled, and the voltage at the "+" input end of CJ0311 is higher than the voltage at the "-" input end, and its output end outputs a high level, the transistor T is turned on, the relay J is energized and attracted, and its contact JK is closed, and the brake light L is in a normal lighting state. After the driver releases the brake switch Kl, the capacitor C discharges through the resistor R7. When the voltage on the capacitor C is lower than 6V, the voltage at the "+" input end of CJ0311 is lower than the voltage at its "-" input end, and its output end outputs a low level, the transistor T is turned off, the relay J is released, and its contact JK is disconnected, and the brake light goes out, which plays a role in delaying the turning off of the brake light. In the figure, J uses a 12V relay.