CN211995384U

CN211995384U - Automobile brake lamp monitor based on Schmitt trigger

Info

Publication number: CN211995384U
Application number: CN202020010640.1U
Authority: CN
Inventors: 崔建国; 宁永香; 崔建峰; 崔燚; 李光序
Original assignee: Shanxi Institute of Technology
Current assignee: Shanxi Institute of Technology
Priority date: 2020-01-03
Filing date: 2020-01-03
Publication date: 2020-11-24
Anticipated expiration: 2030-01-03

Abstract

The utility model discloses an automobile brake light monitor based on Schmitt trigger, which comprises a switch S1 circuit, a brake light circuit, a Schmitt trigger circuit, an LED warning circuit and a sound warning circuit; the brake lamp circuit consists of two brake bulbs LA1 and LA2 which are connected in parallel; the Schmitt trigger circuit is composed of two PNP triodes Q₁、Q₂And a resistance R₁、R₂、R₃、R₄、R₅Potentiometer P₁Forming; power supply 1The 2V power supply is sequentially connected with an E-C electrode of a transistor Q3, a resistor R6, a forward Light Emitting Diode (LED) and a working place through a switch S1 to form the LED warning circuit; the power supply 12V is connected with the E-C pole of the transistor Q4, the direct current buzzer and the working ground in sequence through the switch S1 to form the sound warning circuit, and the collector of the transistor Q3 is connected with the base of the transistor Q4.

Description

Automobile brake lamp monitor based on Schmitt trigger

Technical Field

The utility model relates to a technology of an automobile brake lamp monitor based on a Schmitt trigger, which is based on the brake system of a Bucky sedan, designs an automobile brake lamp monitor, converts the good and different pressure drops when damaged of a left brake lamp and a right brake lamp into the input voltage of the Schmitt trigger consisting of two transistors, controls whether a Schmitt trigger circuit works or not by the voltage, and controls the output of the trigger to give an alarm by sound and light; when the two brake lamps work normally, the light-emitting diode is normally on, and the buzzer is silent; when both the brake lights are damaged, the light-emitting diode is turned off forever, and the buzzer alarms continuously; when one of the light-emitting diodes is damaged, the light-emitting diode is briefly lightened, then is extinguished, and then the buzzer continuously gives an alarm.

Background

The automobile brake lamp is a lamp which is lighted when a vehicle is braked, generally has red color, plays a role of warning the following vehicle, and is mainly used for reminding the following vehicle that the automobile needs to decelerate or stop, and the rear-end collision accident can be easily caused if the brake lamp is used wrongly or has a problem.

Nowadays, the automobile brake lamp is more important, and should be kept in a good working state at the moment when the traffic is increasingly crowded, and if the automobile brake lamp is damaged, the automobile brake lamp should be replaced or repaired in time.

At present, almost all electric circuit parts of automobiles do not adopt any measures for monitoring the brake lamps, the technology is blank in the industry, if the working states of two brake lamps need to be checked, only one brake lamp is difficult to check, and only a second brake lamp can be used for observing whether the brake lamps are normally high or not outside the automobile.

The brake light monitoring circuit for automobile is designed based on the brake system of Buckyue car, and has the core of one Schmitt trigger circuit to monitor the work state of two brake lights and to indicate the normal work state of the brake lights with LED and active buzzer.

The circuit can be directly applied to brake lamp control circuits of almost all vehicle types as a module circuit, or integrated in a vehicle Body Control Module (BCM) of an automobile to be used as a component of the BCM.

Disclosure of Invention

The utility model aims to solve the technical problem that an automobile brake light monitor that simple structure, low in cost, use reliably, the commonality is stronger is provided.

In order to achieve the purpose, the utility model provides an automobile brake light monitor based on Schmitt trigger, which comprises a switch S1 circuit, a brake light circuit, a Schmitt trigger circuit, an LED warning circuit and a sound warning circuit; the brake lamp circuit consists of two brake bulbs LA1 and LA2 which are connected in parallel, 12V power supply is connected with the upper ends of LA1 and LA2 through the switch S1 circuit, and LA1 and LA2 are connected with a working place; the Schmitt trigger circuit is composed of two PNP triodes Q₁、Q₂And a resistance R₁、R₂、R₃、R₄、R₅Potentiometer P₁The 12V power supply is simultaneously connected with the upper ends of a resistor R2 and a resistor R4 through the switch S1 circuit, the lower end of the resistor R2 is simultaneously connected with the emitter of a transistor Q1 and the emitter of a transistor Q2, the lower end of a resistor R4 is connected with the collector of the transistor Q1 through a resistor R3, the collector of Q1 is sequentially connected and operated through the resistor R1 and a potentiometer P1, the connection point of the resistors R4 and R3 is connected with the base of the transistor Q2, and the collector of Q2 is connected and operated through a resistor R5; the power supply 12V is sequentially connected with an E-C electrode of a transistor Q3, a resistor R6, a forward light emitting diode LED and a working ground through a switch S1 to form the LED warning circuit, and a collector electrode of the transistor Q2 is connected with a base electrode of a transistor Q3; the 12V power supply is connected with the E-C electrode of the transistor Q4, the direct current buzzer and the working place in sequence through the switch S1 to form the sound warning circuit, and the transistor Q3Is connected to the base of transistor Q4.

In the Schmitt trigger circuit, the sliding end of the potentiometer P1 is connected with the lower end of the resistor R1.

Drawings

Fig. 1, 2, and 3 are included to provide a further understanding of the present invention and form a part of the present application, and fig. 1 is a schematic diagram of a schmitt trigger circuit. Fig. 2 is a schematic diagram of the voltage transfer characteristics of the schmitt circuit. Fig. 3 is an electrical schematic diagram of a brake light monitor for a car based on a schmitt trigger.

Detailed Description

Structure and working principle of Schmitt trigger

Now that the schmitt trigger is used, the circuit structure and the operation principle of the schmitt trigger will be briefly described.

A schmitt trigger is a circuit often used in pulse waveform conversion, and is sometimes simply referred to as a schmitt circuit. Schmitt circuits are widely used, and not only are integrated circuit products independently manufactured, such as TTL circuit integrated Schmitt trigger circuit 7413; it is also possible to construct a schmitt circuit with discrete components, as shown in fig. 1, consisting of two NPN transistors T₁、T₂And a resistance R₁、R₂、R_EAnd (4) forming.

The Schmitt circuit in FIG. 1 is implemented by a common emitter resistor R_EThe coupled two-stage positive feedback amplifier assumes that the conduction voltage drop of the emitter of the triode is 0.7V, and then when the voltage mu of the input end is_IAt low level (mu)_I= 0), must have

μ_I-μ_E=μ_BE1<0.7V

Then T₁Will be cut off and T₂And conducting in saturation. Mu.s of_IGradually increase and make mu_BE1>At 0.7V, T₁Enters a conducting state and has the following positive feedback process

Thereby enabling the circuit to rapidly enter T₁Saturated conduction, T₂The off state.

Mu.s of_IGradually decreases from high level to mu_BE1Only about 0.7V, i_C1Initially decreases, thus causing another positive feedback process

Make the circuit return to T quickly₁Cut-off, T₂Saturated conducting state.

It can be seen that no matter T₂The change from on to off or from off to on is accompanied by a positive feedback process to make the output voltage mu_OBoth the rising and falling edges of (a) are steep.

At the same time due to R₁>R₂So that T₁μ at saturation conduction_EThe value must be lower than T₂μ at saturation conduction_EThe value is obtained. Thus, T₁The input voltage at the time of change from off to on is necessarily higher than T₁The input voltage at the time of change from on to off, and the voltage transfer characteristic shown in fig. 2 is obtained. Usually with V_T+And V_T-Respectively represent mu_IRising T₁Input voltage and μ when changing from off to on_IAt time of descent T₁The input voltage at the time of turning from on to off.

And will V_T+Referred to as the forward threshold voltage, will V_T-Referred to as negative threshold voltage, | V_T+-V_T-|=ΔV_TReferred to as the back-off voltage. This type of voltage transfer characteristic of fig. 2 is also referred to as a schmitt trigger characteristic.

Working principle of automobile brake lamp monitor based on Schmitt trigger

The electrical schematic diagram of the design is shown in fig. 3, and it can be seen that the circuit system comprises a vehicle lamp circuit consisting of a left brake lamp and a right brake lamp, a Schmitt trigger circuit consisting of two PNP triodes and a resistor, and a current amplifierThe large circuit, the LED warning circuit, the sound warning circuit and the like. Take a Buckyue car as an example, wherein S₁For the contact combination switch of the brake lamp relay of the Buckyue car, the relay is controlled by a car Body Control Module (BCM), and for the convenience of understanding or description, the switch S is temporarily considered₁Namely the automobile brake pedal. LA₁、LA₂Is a left brake lamp and a right brake lamp.

The requirements of our design are: when a driver steps on a brake and the two brake lamps operate well, the LED lamps are normally on and the sound warning does not work; when one brake lamp fails, the LED lamp is turned on briefly and then turned off, and then continuous sound alarm is started; in case of failure of both the brake lights, the LED lights can never be on and the sound is continuously given an alarm.

Schmitt trigger circuit

The Schmitt trigger circuit in FIG. 3 consists of two PNP transistors Q₁、Q₂And a resistance R₁、R₂、R₃、R₄、R₅Potentiometer P₁And (4) forming.

Compared with fig. 1, the two schmitt circuits are similar in structure, but different in structure, the schmitt circuit of fig. 1 is composed of two NPN triodes, and the schmitt circuit of fig. 3 is composed of two PNP triodes, and the positive feedback process path of the two-stage positive feedback amplifier is different from the above one due to the different polarities of the triodes, and the working principle of the schmitt circuit of fig. 3 is analyzed as follows.

The Schmitt circuit in FIG. 3 is implemented by a common emitter resistor R₂The coupled two-stage positive feedback amplifier assumes that the conduction voltage drop of the emitter junction of the PNP triode is 0.6V, and then the voltage at the input end of the Schmitt circuit is high level (u)_AApproximately equal to 12V), must have mu_Q1-E-μ_Q1-B=μ_Q1-EB<0.6V, then Q₁Will be turned off and Q₂And conducting in saturation. Mu in this case_Q1-EFinger triode Q₁Emitter voltage of (2), other operating point voltage with reference to [ mu ]_Q1-EIt is understood that no further description is provided.

Mu.s of_AThe level is gradually lowered and μ_Q1-EB>0.6When V is, Q₁Enters a micro-conduction state and has the following positive feedback process

The strong positive feedback causes the Schmitt circuit to be rapidly converted into Q₁Saturated on, Q₂In the off state, this positive feedback is called positive rising edge feedback.

Mu.s of_AThe level is gradually increased and increased to μ_Q1-EBWhen the voltage is only about 0.6V, i_Q1-CStarts to decrease and then initiates another positive feedback process.

Strong positive feedback causes the circuit to return rapidly to Q₁Cutoff, Q₂Saturated conduction, this positive feedback is called falling edge positive feedback.

Also shown by the parameters in FIG. 3, since (R)₁+P₁）<R₅Therefore Q₁μ at saturation conduction_EThe value must be lower than Q₂μ at saturation conduction_EValue, therefore, Q₁The input voltage at the time of change from off to on is necessarily higher than Q₁Input voltage, Q, at the time of change from on to off₁The input voltage at the time of turning from off to on is referred to as the rising edge threshold voltage V of the Schmitt circuit_T+A value greater than 0.6V; q₁The input voltage at the time of turning from on to off is referred to as the falling edge threshold voltage V of the Schmitt circuit_T-Its value is about 0.6V.

Working principle of automobile brake lamp monitor

As shown in FIG. 3, the working voltage of the monitor (i.e. the voltage at the input end of the Schmitt circuit) depends on the output end of the brake lamp relay of the Buckyue car to be connected with two brake lamps LA₁And LA₂Voltage drop U across the conductor_XNote that the voltage drop across the wire,rather than the potential at point a.

Suppose a triode Q₁The conduction voltage drop of the emitter junction is 0.6V, so that the voltage drop U is reduced at two ends of the wire_XMust be greater than 0.6V and if the 0.6V drop is not achieved, a 5A diode must be forward-conducting in each string.

The working principle of the automobile brake lamp monitor is analyzed according to three conditions that two brake lamps are intact, one brake lamp is broken and two brake lamps are broken.

Two brake lights all work normally

Transistor Q in fig. 3₁And Q₂Forming a Schmitt trigger consisting of a voltage drop U across the lamp supply line_XWhen the two lamps are lighted, the voltage drop of the two parallel filaments is slightly less than 12V, and the voltage drop of the conducting wire U is reduced_X>0.6V, with reference to the positive feedback portion of the rising edge of the Schmitt circuit described above, the strong positive feedback causes the Schmitt circuit to rapidly switch to Q₁Saturated on, Q₂The off state.

At this time, the Schmitt circuit outputs a low level, transistor Q₃The base level being low, triggering a transistor Q₃Conducting to make the light emitting diode D₁Stable "sustained" luminescence; transistor Q₄And when the direct current buzzer is cut off, the direct current buzzer makes a mute sound.

The duration here refers to the time when the driver steps on the brake, the driver moves the brake, the monitor circuit is not powered, and the light emitting diode D₁Naturally, it will extinguish.

One brake light is normal and the other is broken

If one brake lamp is suddenly damaged, the current is only consumed by the other brake lamp, the filament voltage is slightly higher than that when the two brake lamps are normal, and the lead voltage drop U is realized_XApproximately equal to 0.6V, due to the hysteresis characteristic of the Schmitt circuit, the output low level state of the Schmitt circuit cannot be changed immediately, and the light emitting diode D₁The light is continuously emitted for a short time, and the buzzer is continuously silent.

Schmitt circuit falling edge positive and negative as described above with reference toFeedback section, strong positive feedback, causes the circuit to return rapidly to Q₁Cutoff, Q₂Saturated conducting state. At this time, the Schmitt circuit outputs a high level, transistor Q₃Base level is high, transistor Q₃Cut off to make the light emitting diode D₁Extinguishing; transistor Q₄And when the switch is switched on, the direct current buzzer continuously gives an alarm.

Note observation and listening D₁The light emitting (light indication) and the buzzer alarm (sound alarm) have time difference and cannot occur simultaneously.

Two brake lights are abnormal

If both brake lamps are damaged, the filament voltage is about 12V, and the lead voltage drop U in FIG. 3 is_X<0.6V, the Schmitt circuit does not work, the Schmitt circuit outputs high level, the light-emitting diode can not emit light any more, and the direct current buzzer continuously alarms.

The duration here refers to the time when the driver steps on the brake, the driver moves the brake, the monitor circuit is not powered, and the buzzer naturally makes a silent sound.

Debugging and attention points

The hysteresis of Schmitt trigger in the circuit of the monitor, i.e. the sensitivity of the monitor, can be set by means of a potentiometer P₁Set within a narrow range. The indication that the potentiometer is adjusted to the best state is that a light indication light emitting diode D is caused under the condition that a brake lamp is damaged₁Limited by temporary luminescence, D₁After the light is emitted for a short time and then is extinguished, the buzzer starts to alarm continuously.

If you find that the monitor circuit is disturbed, i.e. whenever the brake led D is depressed₁All under the conditions of light emitting and buzzer silence, at this time, the transistor Q can be switched on₃、Q₄Are replaced by NPN type triodes.

If so, the operation of the circuit indicates the correct reversal of state, i.e. the light emitting diode D₁The buzzer is silent, which indicates that the two brake lamps are intact; and D₁The brake lamp is damaged by light emitting and buzzer alarming.

At this time, the transistorQ₃、Q₄Should be connected to the positive supply, and Q₃The emitter being connected to a resistor R₆Upper, Q₄The emitter is connected to the buzzer.

However, it should be noted that it is not possible to determine whether both brake lights are defective or whether one brake light is defective, i.e. once D has been detected₁When lighting, you may have to change one or both lights indefinitely.

The design skillfully solves the problem of monitoring or alarming the fault of the brake lamp by utilizing a Schmitt trigger, fills up the blank of the industry, provides monitoring basis for the state when only one brake lamp is damaged by adjusting the time (namely, hysteresis time) of positive feedback of a Schmitt circuit, ensures that the monitoring of three states of damage, good damage and good damage of the two brake lamps have different expression forms, is helpful for a driver to easily judge the running condition of the brake lamp by one person, and is convenient for replacement or maintenance.

Because the power supply of the high-level brake lamp of the Buckyue sedan car is not controlled by a brake lamp relay but directly controlled by a car Body Control Module (BCM), the design can not play a role in warning the damage of the high-level brake lamp.

In addition, if the left brake lamp and the right brake lamp adopt LED brake bulbs rather than commonly used halogen bulbs, because the working current of the LED bulbs is lower than that of the halogen bulbs, the input voltage of the Shang Si Mi Te circuit changes correspondingly, and the voltage drop U at the two ends of the power supply lead of the LED bulbs is reduced_XIn order to adapt to the change, the type of the diode connected in series with each vehicle lamp needs to be adjusted, so that the forward voltage drop of the connected diode is increased to meet the requirement of the threshold voltage of the Schmitt circuit.

Claims

1. A kind of car brake light monitor based on Schmitt trigger, characterized by that: the automobile brake lamp monitor comprises a switch S1 circuit, a brake lamp circuit, a Schmitt trigger circuit, an LED warning circuit and a sound warning circuit; the brake lamp circuit consists of two brake bulbs LA1 and LA2 which are connected in parallel, 12V power supply is simultaneously connected with the upper ends of LA1 and LA2 through the switch S1 circuit, and LA1 and LA2 are simultaneously connectedConnecting a working ground; the Schmitt trigger circuit is composed of two PNP triodes Q₁、Q₂And a resistance R₁、R₂、R₃、R₄、R₅Potentiometer P₁The 12V power supply is simultaneously connected with the upper ends of a resistor R2 and a resistor R4 through the switch S1 circuit, the lower end of the resistor R2 is simultaneously connected with the emitter of a transistor Q1 and the emitter of a transistor Q2, the lower end of a resistor R4 is connected with the collector of the transistor Q1 through a resistor R3, the collector of Q1 is sequentially connected and operated through the resistor R1 and a potentiometer P1, the connection point of the resistors R4 and R3 is connected with the base of the transistor Q2, and the collector of Q2 is connected and operated through a resistor R5; the 12V power supply is sequentially connected with an E-C electrode of a transistor Q3, a resistor R6, a forward light emitting diode LED and an LED warning circuit which is formed by working through a switch S1, and a collector electrode of the transistor Q2 is connected with a base electrode of a transistor Q3; the 12V power supply is connected with an E-C electrode of a transistor Q4, a direct current buzzer and a working ground through a switch S1 in sequence to form the sound warning circuit, and a collector electrode of a transistor Q3 is connected with a base electrode of a transistor Q4.

2. The scott trigger-based automotive brake light monitor of claim 1, wherein: in the Schmitt trigger circuit, the sliding end of the potentiometer P1 is connected with the lower end of the resistor R1.