Showing posts with label Automotive Projects. Show all posts
Showing posts with label Automotive Projects. Show all posts

Car Reversing Horn With Flasher

Here is a simple circuit that starts playing the car horn whenever your car is in reverse gear. The circuit (1) employs dual timer NE556 to generate the sound. One of the timers is wired as an astable multivibrator to generate the tone and the other is wired as a monostable multivibrator. Working of the circuit is simple. When the car is in reverse gear, reverse-gear switch S1 of the car gets shorted and the monostable timer triggers to give a high output. As a result, the junction of diodes D1 and D2 goes high for a few seconds depending on the time period developed through resistor R4 and capacitor C4.At this point, the astable multivibrator is enabled to start oscillating. The output of the astable multivibrator is fed to the speaker through capacitor C6.
Car reversing horn diagram:
car-reverse-horn-circuit-diagram
The speaker, in turn, produces sound until the output of the monostable is high. When the junction of diodes D1 and D2 is low, the astable multivibrator is disabled to stop oscillating. The output of the astable multivibrator is fed to the speaker through capacitor C6. The speaker, in turn, does not produce sound. Assemble the circuit on a general-purpose PCB and enclose in a suitable cabinet.Connect the circuit to the car reverse switch through two wires such that S1 shorts when the car gear is reversed and is open otherwise. To power the circuit, use the car battery.
Flasher diagram:
flasher-circuit-diagram
The flasher circuit (shown in Fig. 2) is built around timer NE555, which is wired as an astable multi-vibrator that outputs square wave at its pin 3. A 10W auto bulb is used for flasher. The flashing rate of the bulb is decided by preset VR1.
Assemble the circuit on a general-purpose PCB and enclose in a suitable cabinet. The flasher bulb can be mounted at the car’s rear side in a reflector or a narrow painted suitable enclosure. EFY note. A higher-wattage bulb may reduce the intensity of the head-light. You can enclose both the car-reversing horn and flasher circuits together or separately in a cabinet in your car.
Author: Ashok K. Doctor - Copyright: Electronics For You Magazine
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Car Battery Saver Circuit

Prevents the complete discharge of the battery when the door is left open accidentally
I recently forgot to close the door of my car after parking in the garage and I found the battery completely exhausted after the week-end, when I tried to start the engine on Monday morning. This inconvenience prompted me to design a simple circuit, capable of switching-off automatically after a few minutes the inside courtesy lamp, the real culprit for the damage.
Circuit operation:
When the door is opened, SW1 closes, the circuit is powered and the lamp is on. C1 starts charging slowly through R1 and when a voltage of 2/3 the supply is reached at pins #2 and #6 of IC1, the internal comparator changes the state of the flip-flop, the voltage at pin #3 falls to zero and the lamp will switch-off. The lamp will remain in the off state as the door is closed and will illuminate only when the door will be opened again. The final result is a three-terminal device in which two terminals are used to connect the circuit in series to the lamp and the existing door-switch. The third terminal is connected to the 12V positive supply.
Circuit diagram :
Car Battery Saver Circuit Diagram
Notes:
  • With the values specified for R1 and C1, the lamp will stay on for about 9 minutes and 30 seconds.
  • The time delay can be changed by varying R1 and/or C1 values.
  • The circuit can be bypassed by the usually existing switch that allows the interior lamp to illuminate continuously, even when the door is closed: this connection is shown in dotted lines.
  • Current drawing when the circuit is off: 150µA.
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Brake Light Signal Module

Generates 4 short flashes, followed by a steady on light Can drive LED Arrays at currents up to 1 Amp
Circuits of this kind are intended to drive LED Arrays in order to create more visibility and conspicuity when a vehicle is stopped or stopping. This circuit, in particular, will emit a visual alerting signal of 4 short flashes, followed by a steady on light that remains steady on as long as the brakes are applied.
Circuit operation:
IC1 internal oscillator generates a square wave whose frequency is divided 64 times by the flip-flops contained in the chip in order to obtain about 1 to 4Hz at pin #4: this is the LED Array flashing frequency and can be set to the desired value by means of R3. A positive signal at D1 Cathode stops the oscillator after 5 pulses are counted. C2 and R1 automatically reset the IC whenever the brakes are applied. Q1 is the LED Array driver: LEDs will be on when pin #4 of IC1 goes low.
Circuit Diagram:
Brake Light Signal Module Circuit Diagram
Parts:
R1_____________10K 1/4W Resistor
R2____________220K 1/4W Resistor
R3____________500K 1/2W Trimmer, Cermet or Carbon
R4______________1K8 1/4W Resistor (See Note)
R5______________1K8 1/4W Resistor
C1_____________47µF 25V Electrolytic Capacitor
C2______________1µF 25V Electrolytic Capacitor
C3_____________10nF 63V Polyester Capacitor
D1___________1N4148 75V 150mA Diode
IC1____________4060 14 stage ripple counter and oscillator IC
Q1____________BC327 45V 800mA PNP Transistor (See Note)
SW1____________SPST Brake Switch
B1______________12V Vehicle Battery
Note:
  • The transistor type suggested for Q1 will drive LED Arrays at currents up to 500mA. To drive Arrays requiring higher currents (up to 1A and even more) use a BD436 (32V 4A PNP Transistor) for Q1 and a 1K resistor for R4.
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Bicycle Speedometer With Hub Dynamo

The idea for this circuit came when the author had problems with the wireless speedometer on his bicycle. Such a device consists of two parts: the cycle computer itself and a transmitter that is mounted on the front fork. A small magnet is attached to the spokes so that the transmitter sends out a pulse for every revolution of the wheel (as long as everything has been fitted properly). Since the range of the transmitter is limited (about 75 cm), you’ll be lucky if it works straight away. And when the voltage of the battery starts to drop you can forget it. The following circuit gets round these problems.
Picture of the project:
bicycle-speedometer-with-hub-dynamo-circuit
A Shimano NX-30 hub dynamo has 28 poles. This results in 14 complete periods of a 6 V alternating voltage per revolution (when loaded by a lamp; under no load the voltage is much higher). C1, C2, D1 and D2 double the voltage of the AC output. Regulator IC2 keeps the voltage to the transmitter and the divider IC at a safe level (12 V, the same as the original battery). The divider chip (IC1) divides the frequency of the signal from the dynamo by 14, so that a single pulse goes to the transmitter for every revolution of the wheel.
Circuit diagram:
bicycle-speedometer-with-hub-dynamo-circuit-diagram
This pulse enters the circuit at the point where the reed contact was originally. The circuit is built inside the front light, since it has enough room and a cable from the dynamo is already present. The distance to the cycle computer is smaller as well in that case. The following tip can be used if you want to save yourself a few components. In the author’s prototype the counter divided by 16 and the setting for the size of the wheel was adjusted to 16/14th of the real size in the setup of the cycle computer. In that case you can leave out D4, D5 and D8.
Author: Hans Michielsen - Copyright: Elektor Electronics

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Rear Fog Lamp For Vintage Cars

According to current legislation in many countries, vintage cars must also be fitted with a fog lamp at the rear. In modern cars, there is a bit of circuitry associated with the fog lamp switch to prevent the fog lamp from going on when the lights are switched on if the driver forgot to switch it off after the last patch of fog cleared up. The circuit described here extends that technology back in time. The circuit is built around a dual JK flip-flop (type 4027). T3 acts as an emitter follower, and it only supplies power to the circuit when the lights are switched on.
For safety reasons, the supply voltage is tapped off from the number plate lamp (L2), because it is on even if you accidentally drive with only the parking lights on. The wire that leads to the number plate lamp usually originates at the fuse box. As the states of the outputs of IC1a and IC1b are arbitrary when power is switched on, the reset inputs are briefly set high by the combination of C1, R1 and T1 when the lights are switched on (ignition switch on). That causes both Q outputs (pins 1 and 15) to go low. IC1a and IC1b are wired in toggle mode (J and K high).
The Set inputs are tied to ground (inactive). The driver uses pushbutton switch S1 to generate a clock pulse that causes the outputs of the flip-flops to toggle. The debouncing circuit formed by C2, R4 and T2 is essential for obtaining a clean clock pulse, and thus for reliable operation of the circuit. C1 and C2 should preferably be tantalum capacitors. The Q output of IC1b directly drives LED D1 (a low-current type, and yellow according to the regulations). The Q output of IC1a energises relay Re1 via T4 and thus applies power to the rear fog lamp L1.
Circuit diagram:
Rear Fog Lamp For Vintage Cars

Free-wheeling diode D2 protects T4 against inductive voltage spikes that occur when the relay is de-energised. In older-model cars, the charging voltage of the generator or alternator is governed by a mechanical voltage regulator. These regulators are less reliable than the electronic versions used in modern cars. For that reason, a Zener diode voltage-limiter circuit (D3 and R9) is included to keep the voltage at the emitter of T3 below 15 V and thus prevent the 4027 from being destroyed by an excessively high voltage.
The supply voltage for the circuit is tapped off from the fuse box. An accessory terminal is usually present there. Check to make sure it is fed from the ignition switch. The pushbutton switch must be a momentary-contact type (not a latching type). Ensure that the pushbutton and LED have a good ground connection. Fit the LED close to the button.
The following ‘Bosch codes’ are used in the schematic:
  • 15 = +12 V from ignition switch
  • 58K = number plate lamp
  • 86 = relay coil power (+) IN
  • 85 = relay coil power OUT
  • 30 = relay contact (+) IN
  • 87 = relay contact OUT
Author: Eric Vanderseypen - Copyright: Elektor Electronics Magazine
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Central Locking Interface Circuit

Some cheap car alarms do not have a connection for the central locking system. However, in most it should be possible to find a point in the alarm circuit which is high when the alarm is activated and low when it is off. This signal can then be used to drive this relay circuit to operate the central locking system.
Circuit diagram:
Central Locking Interface  Circuit Diagram
The interface circuit converts each toggle of the alarm signal to a brief pulse to operate the two relays which then are then connected in parallel with appropriate contacts on the master solenoid in the central locking system.
Author: Frank Keller  Copyright: Silicon Chip



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Automatic Windshield Washer Control Circuit

Most, if not all, recent cars have an impressive amount of electronics, whether it be ABS brake systems, engine control with injection calculators, airbag activation, or other various functions, called comfort functions. Among them is one which we tend to forget because it has become so common today. It turns on the windshield wipers automatically for a few seconds after the windshield cleaner. This practice is almost indispensable because it avoids any dripping of excess rinse product right in the middle of a just-cleaned windshield.
Unfortunately, many ‘low end’ cars or some of the older cars are not equipped with this automatic function which is a very nice convenience to have. So, since all that is required is a handful of components that any electronics hobbyist worthy of the name already has in his/her drawer, we will discuss the circuit proposed here.
This project is super simple and simply keeps the windshield wiper activated for a few seconds after the windshield washer control contact has been released. While the windshield washer pump is operating, the 12 volts delivered by the battery are present at the terminals and are therefore charging capacitor C1. Once the windshield washer has stopped, this capacitor can only discharge through R2, P1, R3, and the T1 emitter-base junction, due to the presence of diode D1. It thus keeps T1 in the conductive state during a certain time, the exact period of which depends on the setting of P1. T1 in turn saturates T2, which then does the same for T3.
Circuit diagram:
Automatic Windshield Washer Control Circuit Diagram
The Re1 relay is therefore connected which maintains the windshield wiper in operation because its work contact is wired in parallel to the control switch. Once C1 is sufficiently discharged, T1 is blocked, which then blocks T2 and T3 and deactivates relay Re1. The type of components is not really critical, even if we indicate specific reference numbers for T3, any low-power npn transistor with a gain over 25 will work. However, considering the amount of power consumed by the windshield wiper motor, relay Re1 will imperatively be an ‘automobile’ relay.
You can find very low-priced ones at many car accessory shops (and even at some component retailers). These relays maintain contact under 12 volts and often do not have more than one work contact but they are, in general, capable of cutting off about 20 amps. Finally, the only delicate point of this project is to properly identify the control wire for the windshield pump on one hand, and the windshield wiper motor on the other. Observing what is happening at the various connections with a simple voltmeter, should get it right without too much difficulty.
Author: Christian Tavernier  Copyright: Elektor Electronics

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Simple Headlight Reminders Circuit

These two headlight reminder circuits are easy to install and operate on the KISS (Keep It Simple Stupid) principle. The simple circuit involves adding just a 12V piezo buzzer between the lights circuit and a door switch. The buzzer sounds if the lights are left on and you open a door. The disadvantage of this simple circuit is that it's annoying to have the buzzer sound continuously if you want to leave the door open while the lights are on.
Circuit diagram:
simple-headlight-reminders-circuit-diagram
The improved circuit overcomes that problem by adding a 1000µF capacitor and a parallel 100kO resistor in series with the buzzer. Now, when a door is opened, the buzzer gives a brief burst of sound only, while the 1000µF capacitor charges. The 100kO resistor discharges the capacitor when the lights are switched off.
Author: Andrew Gibbs
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Speed limit Alert Circuit

Wireless portable unit Adaptable with most internal combustion engine vehicles
This circuit has been designed to alert the vehicle driver that he/she has reached the maximum fixed speed limit (i.e. in a motorway). It eliminates the necessity of looking at the tachometer and to be distracted from driving. There is a strict relation between engine's RPM and vehicle speed, so this device controls RPM, starting to beep and flashing a LED once per second, when maximum fixed speed is reached. Its outstanding feature lies in the fact that no connection is required from circuit to engine.
Circuit diagram:

Parts:
R1,R2,R19_______1K   1/4W Resistors
R3-R6,R13,R17_100K   1/4W Resistors
R7,R15__________1M   1/4W Resistors
R8_____________50K   1/2W Trimmer Cermet
R9____________470R   1/4W Resistor
R10___________470K   1/4W Resistor
R11___________100K   1/2W Trimmer Cermet (see notes)
R12___________220K   1/4W Resistor (see notes)
R14,R16________68K   1/4W Resistors
R18____________22K   1/4W Resistor
R20___________150R   1/4W Resistor (see notes)
C1,C7_________100µF  25V Electrolytic Capacitors
C2,C3_________330nF  63V Polyester Capacitors
C4-C6___________4µ7  25V Electrolytic Capacitors
D1,D5______Red LEDs  3 or 5mm.
D2,D3________1N4148  75V 150mA Diodes
D4________BZX79C7V5  7.5V 500mW Zener Diode
IC1__________CA3140  or TL061 Op-amp IC
IC2____________4069  Hex Inverter IC
IC3____________4098  or 4528 Dual Monostable Multivibrator IC
Q1,Q2_________BC238  25V 100mA NPN Transistors
L1_____________10mH  miniature Inductor (see notes)
BZ1___________Piezo sounder (incorporating 3KHz oscillator)
SW1____________SPST  Slider Switch
B1_______________9V  PP3 Battery (see notes)
Clip for PP3 Battery
Circuit Operation:
IC1 forms a differential amplifier for the electromagnetic pulses generated by the engine sparking-plugs, picked-up by sensor coil L1. IC2A further amplifies the pulses and IC2B to IC2F inverters provide clean pulse squaring. The monostable multivibrator IC3A is used as a frequency discriminator, its pin 6 going firmly high when speed limit (settled by R11) is reached. IC3B, the transistors and associate components provide timings for the signaling part, formed by LED D5 and piezo sounder BZ1. D3 introduces a small amount of hysteresis.

Notes:
  • D1 is necessary at set-up to monitor the sparking-plugs emission, thus allowing to find easily the best placement for the device on the dashboard or close to it. After the setting is done, D1 & R9 can be omitted or switched-off, with battery savings.
  • During the preceding operation R8 must be adjusted for better results. The best setting of this trimmer is usually obtained when its value lies between 10 and 20K.
  • You must do this first setting when the engine is on but the vehicle is stationary.
  • The final simplest setting can be made with the help of a second person. Drive the vehicle and reach the speed needed. The helper must adjust the trimmer R11 until the device operates the beeper and D5. Reducing vehicle's speed the beep must stop.
  • L1 can be a 10mH small inductor usually sold in the form of a tiny rectangular plastic box. If you need an higher sensitivity you can build a special coil, winding 130 to 150 turns of 0.2 mm. enameled wire on a 5 cm. diameter former (e.g. a can). Extract the coil from the former and tape it with insulating tape making thus a stand-alone coil.
  • Current drawing is about 10mA. If you intend to use the car 12V battery, you can connect the device to the lighter socket. In this case R20 must be 330R.
  • Depending on the engine's cylinders number, R11 can be unable to set the device properly. In some cases you must use R11=200K and R12=100K or less.
  • If you need to set-up the device on the bench, a sine or square wave variable generator is required.
  • o calculate the frequency relation to RPM in a four strokes engine you can use the following formula:
    Hz= (Number of cylinders * RPM) / 120.
    For a two strokes engine the formula is: Hz= (Number of cylinders * RPM) / 60.
    Thus, for a car with a four strokes engine and four cylinders the resulting frequency @ 3000 RPM is 100Hz.
  • Temporarily disconnect C2 from IC1 pin 6. Connect the generator output across C2 and Ground. Set the generator frequency to e.g. 100Hz and trim R11 until you will hear the beeps and LED D5 will start flashing. Reducing the frequency to 99 or 98 Hz, beeping and flashing must stop.
  • Please note that this circuit is not suited to Diesel engines.
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Rear Light After Glow (For Bicycles)

This article is of interest only to readers whose bicycle lights are powered by a dynamo. The laws on bicycle lights in the United Kingdom are stricter than in other countries and a dynamo is, therefore, a rarity in this country. From the point of view of traffic safety it is advisable (in UK obligatory) for cyclists to have the rear lamp of their bicycle to light even when they are at standstill.
In principle, it is not very difficult to modify the existing rear light with afterglow: all this needs is a large enough energy reservoir. Since the after-glow is required for short periods of time only, a battery is not required: a large value capacitor, say, 1 F, is quite sufficient.As the diagram shows, in the present circuit, the normal rear light bulb is replaced by two series-connected bright LEDs, D2 and D3. These are clearly visible with a current of only 6 mA (compared with 50 mA of the bulb).
The current is set with series resistor R1. The LEDs are shunted by the 1 F capacitor, C1. Since the working voltage of this component is only 5.5 V, it is, in spite of its high value, physically small. An effective regulator is needed to limit the dynamo voltage adequately. Normal regulators cannot be used here, since they do not work at low voltages. Moreover, such a device would discharge the capacitor when the cycle is at standstill.
Circuit diagram :
Rear Light After Glow (For Bicycles)

Fortunately, there is a low-drop type that meets the present requirements nicely: the Type LP2950CZ5.0. Of course, the dynamo output voltage needs to be rectified before it can be applied to the regulator. In the present circuit, this is effected by half-wave rectifier D1 and buffer capacitor C2. Diode D1 is a Schottky type to keep any losses low – important for this application, because the ground connection via the bicycle frame usually causes some losses as well. The value of buffer capacitor has been chosen well above requirements to ensure that C1 is charged during the negative half cycles of the dynamo voltage.
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LED Bike Light Circuit Project

On my mountain bike I always used to have one of those well-known flashing LED lights from the high street shop. These often gave me trouble with flat batteries and lights that fell off. As an electronics student I thought: “this can be done better”. First I bought another front wheel, one which has a dynamo already built in the hub. This supplied a nice sine wave of 30 Vpp (at no load). With this knowledge I designed a simple power supply. The transistors that are used are type BD911.These are a bit of an over-kill, but there were plenty of these at my school, so that is why I used them. Something a little smaller will also work. The power supply is connected to an astable multi-vibrator. This alternately drives the front light and the rear light.
The frequency is determined by the RC time-constant of R3 and C3, and R2 and C4. This time can be calculated with the formula: t = R3×C3 = 20×103×10×10-6 = 0.2 s You can use a 22k (common value) for R2 and R3, that doesn’t make much difference. On a small piece of prototyping board are six LEDs with a voltage dropping resistor in series with each pair of LEDs.
Circuit diagram:
LED Bike Light Circuit Project

Such a PCB is used for both the front and the rear of the bike. Of course, you use white LEDs for the front and red ones for the rear. The PCB with the main circuit is mounted under the seat, where it is safe and has been working for more than a year now. There are a few things I would change for the next revision. An on/off switch would be nice. And if the whole circuit was built with SMD parts it could be mounted near the front light. This would also be more convenient when routing the wiring. Now the cable from the dynamo goes all the way to the seat and from there to the front and rear lights.
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A Simple Fog Lamp Sensor

For several years now, a rear fog lamp has been mandatory for trailers and caravans in order to improve visibility under foggy conditions. When this fog lamp is switched on, the fog lamp of the pulling vehicle must be switched of to avoid irritating reflections. For this purpose, a mechanical switch is now built into the 13-way female connector in order to switch of the fog lamp of the pulling vehicle and switch on the fog lamp of the trailer or caravan. For anyone who uses a 7-way connector, this switching can also be implemented electronically with the aid of the circuit illustrated here.
Circuit diagram:
Fog Lamp Sensor Circuit Daigram
Here a type P521 optocoupler detects whether the fog lamp of the caravan or trailer is connected. If the fog lamp is switched on in the car, a current flows through the caravan fog lamp via diodes D1 and D2. This causes the LED in the optocoupler to light up, with the result that the photo-transistor conducts and energies the relay via transistor T1. The relay switches of the fog lamp of the car. For anyone who’s not all thumbs, this small circuit can easily be built on a small piece of perforated circuit board and then fitted somewhere close to the rear lamp fitting of the pulling vehicle.
Author :Harrie Dogge Copyright  :Elektor Electronics 2008
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Motor Bike Headlight Controller Circuit Diagram

This circuit automatically turns a motor cycle's headlight on and off, independently of both the light and ignition switches, provided the battery is fully charged. The first stage uses the 22O resistor and ZD1 to hold transistor Q1 off while the motor is not running; it draws about 2mA. Once the battery voltage exceeds 7.0V during charging, Q1 begins to turn on.
The last stage uses the 22O resistor and ZD2 to turn on transistor Q2, which pulls the base of Q1 down, switching it hard on. In conjunction with the Vbe drop of Q2, ZD2 will turn off Q2 at a battery voltage of about 6.7V. In practice, this means that the headlight will be on most of the time while the motor is running and charging the battery. Heatsinks are required for both transistors. The circuit can be mounted adjacent to the battery with a single lead going to the headlight power feed.
Circuit Diagram:
Parts Description
P1 5R - 3W
R1 220R -1W
R2 1R - 1W
R3 22R - 5W
R4 22R - 5W
Q1 BD139
Q2 MJ4502
D1 6.2V - 1WZener
D2 6.2V - 1WZener
B1 6.6V - 7.2V
F1 Fuse 15A
Lp1 DIP Beam 6V-25W Halogen
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Car Bulb Power Flasher

Derived from the Two-wire Lamp Flasher design, hosted on RED Free Circuit Designs since 1999, this astonishingly simple circuit allows one or two powerful 12V 21W car bulbs to be driven in flashing mode by means of a power MosFet.
Devices of this kind are particularly suited for road, traffic and yard alerts and in all cases where mains supply is not available but a powerful flashing light is yet necessary.
Circuit Diagram:

Parts Description
R1 6.8K
R2 220K
R3 22K
C1 100uF-25V
C2 10u-25V
D1 1N4002
Q1 BC557
Q2 IRF530
LP1 12V-21W Car Filament Bulb (See Notes)
SW1 SPST Switch (3 Amp minimum)
Notes:
  • Flashing frequency can be varied within a limited range by changing C1 value.
  • As high dc currents are involved, please use suitably sized cables for battery and bulb(s) connections.
Source : www.redcircuits.com
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Park-Aid Modification Circuit

Three-step beeps signal bumper-barrier distance, Infra-red operation, indoor use
This modification was designed on request: some people prefer an audible alert instead of looking at the LED display, making easier the parking operation. The original Park-aid circuit was retained, but please note that the input pins of IC2B, IC2C and IC2D are reversed. LEDs D5, D6 and D7, as also resistors R12, R13 and R14 are omitted. IC2B, IC2C and IC2D outputs drive resistors R15, R16 and R17 through D8, D9 and D10 respectively, in order to change the time constant of a low frequency oscillator based on the 555 timer IC4. This allows the Piezo sounder to start beeping at about 2 times per second when bumper-wall distance is about 20 cm., then to increase the beeps to about 3 per second when bumper-wall distance is about 10 cm. and finally to increase further the beeps frequency to more than 4 beeps per second when the distance is about 6 cm. or less.
Circuit diagram:
Park-Aid Modification Circuit Diagram
Parts:
R15_____________3K3 1/4W Resistor
R16___________330K 1/4W Resistor
R17___________470K 1/4W Resistor
R18___________150K 1/4W Resistor
C6______________1µF 63V Electrolytic or Polyester Capacitor
D8,D9,D10____1N4148 75V 150mA Diodes
IC4_____________555 Timer IC
BZ1___________Piezo sounder (incorporating 3KHz oscillator)
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Speed-Limit Alert

Wireless portable unit, Adaptable with most internal combustion engine vehicles
This circuit has been designed to alert the vehicle driver that he/she has reached the maximum fixed speed limit (i.e. in a motorway). It eliminates the necessity of looking at the tachometer and to be distracted from driving. There is a strict relation between engine's RPM and vehicle speed, so this device controls RPM, starting to beep and flashing a LED once per second, when maximum fixed speed is reached. Its outstanding feature lies in the fact that no connection is required from circuit to engine.
Circuit operation:
IC1 forms a differential amplifier for the electromagnetic pulses generated by the engine sparking-plugs, picked-up by sensor coil L1. IC2A further amplifies the pulses and IC2B to IC2F inverters provide clean pulse squaring. The monostable multivibrator IC3A is used as a frequency discriminator, its pin 6 going firmly high when speed limit (settled by R11) is reached. IC3B, the transistors and associate components provide timings for the signaling part, formed by LED D5 and piezo sounder BZ1. D3 introduces a small amount of hysteresis.
Circuit diagram:
Speed-limit Alert Circuit Diagram
Parts:
R1,R2,R19_______1K 1/4W Resistors
R3-R6,R13,R17_100K 1/4W Resistors
R7,R15__________1M 1/4W Resistors
R8_____________50K 1/2W Trimmer Cermet
R9____________470R 1/4W Resistor
R10___________470K 1/4W Resistor
R11___________100K 1/2W Trimmer Cermet (see notes)
R12___________220K 1/4W Resistor (see notes)
R14,R16________68K 1/4W Resistors
R18____________22K 1/4W Resistor
R20___________150R 1/4W Resistor (see notes)
C1,C7_________100µF 25V Electrolytic Capacitors
C2,C3_________330nF 63V Polyester Capacitors
C4-C6___________4µ7 25V Electrolytic Capacitors
D1,D5______Red LEDs 3 or 5mm.
D2,D3________1N4148 75V 150mA Diodes
D4________BZX79C7V5 7.5V 500mW Zener Diode
IC1__________CA3140 or TL061 Op-amp IC
IC2____________4069 Hex Inverter IC
IC3____________4098 or 4528 Dual Monostable Multivibrator IC
Q1,Q2_________BC238 25V 100mA NPN Transistors
L1_____________10mH miniature Inductor (see notes)
BZ1___________Piezo sounder (incorporating 3KHz oscillator)
SW1____________SPST Slider Switch
B1_______________9V PP3 Battery (see notes) Clip for PP3 Battery
Notes:
  • D1 is necessary at set-up to monitor the sparking-plugs emission, thus allowing to find easily the best placement for the device on the dashboard or close to it. After the setting is done, D1 & R9 can be omitted or switched-off, with battery savings.
  • During the preceding operation R8 must be adjusted for better results. The best setting of this trimmer is usually obtained when its value lies between 10 and 20K.
  • You must do this first setting when the engine is on but the vehicle is stationary.
  • The final simplest setting can be made with the help of a second person. Drive the vehicle and reach the speed needed. The helper must adjust the trimmer R11 until the device operates the beeper and D5. Reducing vehicle's speed the beep must stop.
  • L1 can be a 10mH small inductor usually sold in the form of a tiny rectangular plastic box. If you need an higher sensitivity you can build a special coil, winding 130 to 150 turns of 0.2 mm. enameled wire on a 5 cm. diameter former (e.g. a can). Extract the coil from the former and tape it with insulating tape making thus a stand-alone coil.
  • Current drawing is about 10mA. If you intend to use the car 12V battery, you can connect the device to the lighter socket. In this case R20 must be 330R.
  • Depending on the engine's cylinders number, R11 can be unable to set the device properly. In some cases you must use R11=200K and R12=100K or less.
  • If you need to set-up the device on the bench, a sine or square wave variable generator is required.
  • To calculate the frequency relation to RPM in a four strokes engine you can use the following formula: Hz= (Number of cylinders * RPM) / 120.
  • For a two strokes engine the formula is: Hz= (Number of cylinders * RPM) / 60.
  • Thus, for a car with a four strokes engine and four cylinders the resulting frequency @ 3000 RPM is 100Hz.
  • Temporarily disconnect C2 from IC1 pin 6. Connect the generator output across C2 and Ground. Set the generator frequency to e.g. 100Hz and trim R11 until you will hear the beeps and LED D5 will start flashing. Reducing the frequency to 99 or 98 Hz, beeping and flashing must stop.
  • Please note that this circuit is not suited to Diesel engines.
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Headlight Reminder

With the storm season recently upon us, it’s not uncommon to switch car headlights on during the daytime. Unfortunately, it’s easy to forget to turn them off again when parking, with the result being a flat battery. This circuit will sound an alarm if the ignition switch is moved to the "off" position while the car lights are on, reminding you to turn the lights off before leaving the vehicle.
The circuit is simple but effective. A 555 timer (IC1) is configured as a free-running oscillator to drive a small piezo transducer. The pitch of the transducer is set by the resistor and capacitor connected to pins 2 & 6. Power for the 555 is derived from the dashboard lighting circuit. However, the piezo does not sound during normal operation, because the 555’s reset input (pin 4) is held low by transistor Q1.
Circuit diagram:
headlight-reminder-circuit-diagram
This transistor is switched on whenever accessory power is present, pulling its collector towards ground (0V). If the ignition is switched off but the lighting circuit remains powered, the loss of accessory power results in Q1 switching off and releasing the reset signal to IC1, sounding the alarm. A 220Ω resistor in series with the piezo protects the 555’s output (pin 3). Although most piezo elements have relatively high impedance, this drops as the frequency increases due to their capacitive nature.
The square-wave output on pin 3 includes many harmonics, some extending well into the ultrasonic range. The unit fits easily into a small plastic box. I spliced mine into the wiring running to the cigarette lighter, which includes both accessories and panel lamp circuits as well as a chassis ground wire. The result fits neatly behind the ashtray, with no chassis bashing required!
Author: Bruce Colledge - Copyright: Silicon Chip Electronics
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Car Interior Lights Delay

Most cars do not have delayed interior lights. The circuit presented can put this right. It switches the interior lights of a car on and off gradually. This makes it a lot easier, for instance, to find the ignition keyhole when the lights have gone off after the car door has been closed. Since the circuit must be operated by the door switch, a slight intervention in the wiring of this switch is unavoidable.
When the car door is opened, the door switch closes the lights circuit to earth. When the door is closed (and the switch is open), transistor T1, whose base is linked to the switch, cuts off T2, so that the interior light remains off. When the switch closes (when the door is opened), the base of T1 is at earth level and the transistor is off.
Circuit diagram:
http://www.ecircuitslab.com/2011/06/car-interior-lights-delay.html
Capacitor C1 is charged fairly rapidly via R3 and D1, whereupon T2 comes on so that the interior light is switched on. When the door is closed again, T1 conducts and stops the charging of C1. However, the capacitor is discharged fairly slowly via R5, so that T2 is not turned off immediately.
This ensures that the interior light remains on for a little while and then goes out slowly. The time delays may be varied quite substantially by altering the values of R3, R5, and C1. Circuit IC2 may be one of many types of n-channel power MOSFET, but it should be able to handle drain-source voltages greater than 50 V. In the proto-type, a BUZ74 is used which can handle D-S voltages of up to 500 V.
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Car Boot Lamp Warning (ICM7556)

On many cars, the boot light will not go out until the lid is properly closed. It is all too easy when unloading the car, to leave the lid ajar. If you are unlucky and the car remains unused for some time, the next time you try to start it, the lamp will have drained the battery and you will no doubt utter a few appropriate words. The circuit described here will give a warning of just such a situation. 

A mercury tilt switch is mounted in the boot so that as the lid is closed, its contacts close before the lid is completely shut. The supply for the circuit comes from the switched 12 V to the boot lamp and through the mercury switch. When the lid is properly closed, the boot lamp will go out and the supply to the circuit will go to zero. If however the lid is left ajar, the lamp will be on and the mercury switch will close the circuit. 

Car Boot Lamp Warning (ICM7556) Circuit Diagram

Automotive Circuit Projects

After 5 seconds, the alarm will start to sound, and unless the lid is shut, it will continue for 1 minute to remind you to close the boot properly. The 1-minute operating period will ensure that the alarm does not sound continuously if you are, for example, transporting bulky items and the boot will not fully close. The circuit consists of a dual CMOS timer type 7556 (the bipolar 556 version is unsuitable for this application).

When power is applied to the circuit (i.e. the boot lid is ajar) tantalum capacitors C1 and C2 will ensure that the outputs of the timers are high. After approximately 5 seconds, when the voltage across C2 rises to 2/3 of the supply voltage, timer IC1b will be triggered and its output will go low thereby causing the alarm to sound.

Meanwhile the voltage across C1 is rising much more slowly and after approximately 1 minute, it will have reached 2/3 of the supply voltage. IC1a will now trigger and this will reset IC1b. The alarm will be turned off. IC1a will remain in this state until the boot lid is either closed or opened wider at which point C1 and C2 will be discharged through R6 and the circuit will be ready to start again. 

To calculate the period of the timers use the formula: t = 1.1RC Please note that the capacitor type used in the circuit should be tantalum or electrolytic with a solid electrolyte. The buzzer must be a type suitable for use at D.C. (i.e. one with a built in driver). 


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Lights On!

This circuit ensures that you will never again forget to switch on the lights of your car. As soon as the engine is running, the dipped beams and the sidelights are automatically switched on. The circuit also causes the dipped beams to be extinguished as soon as the main beams are switched on. As you can see from the schematic diagram, no special components are needed.

When the engine is running, the alternator will generate a voltage of more than 14 V. Diode D1 reduces this voltage by 5.6 V and passes it to the base of T1 via R1. Due to the resulting current, T1 conducts. The amplified current flows via R3, the base of T3 and D3 to ground. This causes T3 to also conduct and energize relay Re1.

Lights On! Circuit Diagram
Electronic Lights Circuit Diagram

If the driver now switches on the main beams, a current flows through D2 and R2 into the base of T2, causing this transistor to conduct. As a result, the voltage on the base of T3 drops, causing T3 to cut off and the relay to drop out.

 When the main beams are switched off, the previous situation is restored, and the relay again engages. The dipped beams and the sidelights are switched by the contacts of relay Re1. Diodes D5 and D6 ensure that the sidelights are illuminated if either the dimmed beams or the main beams are switched on. In practice, this means that the sidelights will be on whenever the engine is running, regardless of whether the main beams are switched on.

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