Car handbrake indicator. Free Technical Library article

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Car handbrake warning light

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Encyclopedia of radio electronics and electrical engineering / Automobile. Electronic devices

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The proposed device is designed to supply an intermittent sound and light signal to the driver when starting the car with the handbrake on. Its connection diagram is shown on the example of the Moskvich-2140 car, but can be performed on other car models.

The driver is notified about the violation of the tightness of the hydraulic system of the brake mechanisms of the wheels and the activation of the hand brake of the Moskvich-2140 car using one signal lamp installed on the instrument panel. When the handbrake is applied, the lamp lights up with a constant light, which does not always attract the driver's attention, unlike flashing, and often even experienced drivers forget to turn off the handbrake when starting and moving the car. This causes increased wear of the brake linings, additional load on the engine and misadjustment of the handbrake drive system.

The device whose circuit is shown in the figure consists of a sound generator assembled on transistors VT1, VT2, a multivibrator on transistors VT3, VT4 (the winding of relay K.1 is connected to the VT3 collector circuit); additional switch SB2 and standard elements of electrical equipment - ignition key SA1, sensor SP for tightness of the hydraulic brake actuator, switch SB1 of the hand brake signal lamp and signal lamp HL.

Switch SB2 is installed under the clutch pedal, similar to the brake light switch on the foot brake pedal. When you press the clutch pedal, the contacts of the switch SB2 close, when released, they open.

Car handbrake indicator. Handbrake signaling circuit

The device works as follows. When the SA1 ignition switch is on, the +12 V supply voltage is supplied to the HL lamp and terminal 5 of the device. By closing the contacts of the switch SB1 (handbrake on), the multivibrator and signal lamp are connected to the negative power bus through the circuit: minus 12 V, closed contacts of the switch SB1, terminal 4 of the device, normally closed contacts K1.1, switch SB2 and through the VD1 diode to the lamp HL . The multivibrator starts to work.
Turning on with a frequency of 1 ... 2 Hz, relay K1, with its normally closed contact K1.1, switches the lamp power circuit, and when the contacts of the SB2 switch are closed (the clutch pedal is pressed), the sound generator power circuit is also switched.
The lamp and the generator "give out" an intermittent light and sound signal, respectively. When the contacts of the switch SB1 are opened (the handbrake is off), the lamp and the multivibrator are de-energized.
When the SP switch is actuated (the tightness of the hydraulic drive is broken), the signal lamp will emit a constant light as it usually does with this malfunction. The indication of the on state of the handbrake when the clutch pedal is depressed will be the same - an intermittent sound signal. This is achieved by separating the circuit of the SP switch and the negative power bus of the device with a back-to-back diode VD1, i.e. minus 12 V can be supplied to the device only through terminal 4 and closing the contacts of the SP switch does not affect the operation of the device.

In table. 1 shows the states of the indicators during the actions of the driver with the hand brake (switch SB1) and the clutch pedal (switch SB2) when starting and driving the car with normal and broken tightness of the hydraulic brake drive.

The device is connected by terminals 1, 2 to the switch SB2 of the clutch pedal, terminal 3 - to the contact of the switch SP that has been freed from the conductor (a) (see Fig. 2). The disconnected conductor (a) of the SB1 switch is connected to terminal 4, terminal 5 to the +12 V power bus.

Table 1

	Situation	light indication HL	audible indication HA
1	Power off	0	0
	Normal tightness of hydraulic brakes
2	Handbrake on, car parking	Х	0
3	Trogane and movement of the car with the handbrake off	0	0
4	Starting a car with the handbrake on	Х	Х
5	Driving a car with the handbrake on	Х	0
	Violation of the tightness of the hydraulic drive of the brake
6	Handbrake on (off), car parking	+	0
7	Starting and moving the car with the handbrake off	+	0
8	Starting a car with the handbrake on	+	Х
9	Driving a car with the handbrake on	+	0
Note: 0 - no indication; X - intermittent indication; + permanent indication.

The device uses transistors MP25 with a static current transfer ratio of 20 ... 35, capacitors - C1, C2 - MBM, SZ - K50-6, MLT resistors, relay RES-15 (passport RS4.591.003.P2), sound emitter-capsule DEMSh-1A, switch SB2-microswitch MP-1 with the corresponding fastening elements.

Instead of these, you can use transistors MP26, MP39, MP40 with a current transfer ratio of at least 20, diodes D7A, D226 and D220, D9Zh, E, relays of any type for an operating current of not more than 30 ... 50 mA and a supply voltage of 12 V.
A properly assembled and connected device does not need to be configured. All its elements are located on the printed circuit board and placed in a metal case.
Mounting and mutual arrangement of semiconductor elements are not critical. Dimensions depend mainly on the type of relay and sound emitter used.

Long-term operation of the device has shown its reliability, convenience and necessity.

Publication: cxem.net

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