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

Automatic Headlight Reminder

Do you drive an older car without an automatic "lights-on" warning circuit? If so, you've probably accidentally left the lights on and flattened the battery on one or more occasions. This headlights reminder circuit will prevent that. It's more complicated than other circuits but it's also more versatile. As shown, the circuit uses two low-cost ICs. IC1 is a 555 timer which is wired to operate in astable mode. Its output clocks IC2, a 4017B decade counter. IC2 in turn drives a row of indicator LEDs and also resets IC1 (after about 10s) via transistor Q2.
The circuit works like this:
When the ignition is on, transistor Q1 is also on and this pulls pin 4 of IC1 low. As a result, IC1 is held reset and no clock pulses are fed to IC2. Conversely, if the ignition is turned off, Q1 will turn off and so IC1 will start oscillating and sound the piezo siren. At the same time, IC1 will clock IC2 and so LEDs 1-10 will light in sequence and stop (after about 10s) with the last LED (LED10) remaining on. That's because, when IC2's O9 output (ie, pin 11) goes high, Q2 also turns on and this pulls pin 4 of IC1 low, thus stopping the oscillator (and the siren).
Circuit diagram:
That different colored LEDs are used to make the display look eye-catching but you make all LEDs the same color if you wish. Installing optional diode D1 will alter IC1's frequency and this will alter the display rate. Finally, if the lights are turned off and then back on again, the alarm will automatically retrigger. LED1 is always on if the lights are turned on. If you don't want the LED display, just leave the LEDs out.
Author: L. Marshall - Copyright: Silicon Chip Electronics
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AFX Slot Car Lap Counter

AFX slot car sets are very enjoyable but you can increase the fun with a lap counter. This circuit will count from 00 to 99, with independent counters for each track. The sensing device used is a Hall effect sensor (UGN3503; available from Dick Smith Electronics). One of these sensors is glued under a section of each track (printed side up); between the slot and one of the track rails is the best spot. In this position, it will allow the ground effects magnets on the cars to pass over them. The sensor will provide a voltage of about 3V when a car passes over it and about 2V without a magnetic field. Both counter circuits are identical, with dual op amp IC5 handling the signals from both sensors.
Circuit diagram:
IC5a and IC5b are wired as comparators, with a 2.5V reference derived from zener diode ZD1 via the 10kO and 12kO resistors. Each time the output of IC5a goes high it clocks IC1a, a 4518 BCD counter. NAND gates IC2a & IC2b provide a carry out to the other half of IC1 for a 2-digit display. More counters may be cascaded this way to provide extra digits. The BCD outputs of IC1 drive 7-segment decoders IC3 & IC4 which drive common cathode LED displays. Push-button S1 resets the counters to 00 for both tracks for the start of a new race.
Author: Placid Talia - Copyright: Silicon Chip Electronics
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Lambda Probe Readout For Carburettor Tuning

A lambda probe (or oxygen sensor) can be found on the exhaust system of most cars running on unleaded fuel. Having reached its normal operating temperature (of about 600 degrees Celsius!) the lambda probe supplies an output voltage proportional to the amount of residual oxygen measured in the exhaust gas.

This information is indicative of, among others, the air/fuel ratio supplied by the carburetor(s) and hence the combustion efficiency. In modern car (and motorcycle) engines, this information is used to (electronically) adjust engine parameters like ignition timing and fuel injection. The indicator described here is intended for permanent installation on a motorcycle of which the air/fuel ratio needed to be watched, with the obvious aim engine power tuning after fitting a different set of carburetors. Apart from this obvious technical use the unit’s bright LEDs will no doubt attract the attention of curious motorcyclists.

Lambda Probe Readout For Carburettor Tuning

At the local junkyard a single-wire lambda probe may be salvaged from a wrecked car. Once a suitable nut has been found, the probe can screwed into the exhaust pipe of the motorcycle, at about 30 cm from the cylinders.  Since we’re talking of welding and drilling in an expensive (chrome-plated) exhaust pipe, you may find that actually fitting the probe is best left to specialists!  The starting point for the design of a suitable electronic indicator is that in the noble art of carburetor tuning an air/fuel ratio of 14.7 to 1 is generally considered ‘perfect’, the range covering 16.2 to 1 (‘lean’) to 11.7 to 1 (‘rich’). The perfect ratio typically corresponds to a probe output voltage of 0.45 V. 

 Referring to the circuit diagram, that is the input level at which 5 of the 10 LEDs will light, including the green one, D5. If one of the red LEDs lights, the mixture is definitely too rich. Note that in general it is better to have a mixture that is a little to rich than one that’s on the lean side, hence a yellow LED lights between the green LED and the first red one. Also note that the engine needs to be at its normal operating temperature before a meaningful indication is obtained.
Author : P. G oossens
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Push-Bike Light

Automatic switch-on when it gets dark, 6V or 3V battery operation
This design was primarily intended to allow automatic switch-on of push-bike lights when it gets dark. Obviously, it can be used for any other purpose involving one or more lamps to be switched on and off depending of light intensity. Power can be supplied by any type of battery suitable to be fitted in your bike and having a voltage in the 3 to 6 Volts range.
The Photo resistor R1 should be fitted into the box containing the complete circuit, but a hole should be made in a convenient side of the box to allow the light hitting the sensor. Trim R2 until the desired switching threshold is reached. The setup will require some experimenting, but it should not be difficult.
Circuit diagram:
Push-Bike Light Circuit Diagram
R1_____________Photo resistor (any type)
R2______________22K 1/2W Trimmer Cermet or Carbon type
R3_______________1K 1/4W Resistor
R4_______________2K7 1/4W Resistor
R5_____________330R 1/4W Resistor (See Notes)
R6_______________1R5 1W Resistor (See Notes)
D1____________1N4148 75V 150mA Diode
Q1_____________BC547 45V 200mA NPN Transistor
Q2_____________BD438 45V 4A PNP Transistor
LP1____________Filament Lamp(s) (See Notes)
SW1_____________SPST Toggle or Slider Switch
B1______________6V or 3V Battery (See Notes)
  • In this circuit, the maximum current and voltage delivered to the lamp(s) are limited mainly by R6 (that can't be omitted if a clean and reliable switching is expected). Therefore, the Ohm's Law must be used to calculate the best voltage and current values of the bulbs.
  • For example: at 6V supply, one or more 6V bulbs having a total current drawing of 500mA can be used, but for a total current drawing of 1A, 4.5V bulbs must be chosen, as the voltage drop across R6 will become 1.5V. In this case, R6 should be a 2W type.
  • At 3V supply, R6 value can be lowered to 1 or 0.5 Ohm and the operating voltage of the bulbs should be chosen accordingly, by applying the Ohm's Law.
  • Example: Supply voltage = 3V, R6 = 1R, total current drawing 600mA. Choose 2.2V bulbs as the voltage drop caused by R6 will be 0.6V.
  • At 3V supply, R5 value must be changed to 100R.
  • Stand-by current is less than 500µA, provided R2 value after trimming is set at about 5K or higher: therefore, the power switch SW1 can be omitted. If R2 value is set below 5K the stand-by current will increase substantially.
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Park-Aid Circuit

Three LEDs signal bumper-barrier distance, Infra-red operation, indoor use
This circuit was designed as an aid in parking the car near the garage wall when backing up. LED D7 illuminates when bumper-wall distance is about 20 cm., D7+D6 illuminate at about 10 cm. and D7+D6+D5 at about 6 cm. In this manner you are alerted when approaching too close to the wall. All distances mentioned before can vary, depending on infra-red transmitting and receiving LEDs used and are mostly affected by the color of the reflecting surface. Black surfaces lower greatly the device sensitivity. Obviously, you can use this circuit in other applications like liquids level detection, proximity devices etc.
Circuit operation:
IC1 forms an oscillator driving the infra-red LED by means of 0.8mSec. pulses at 120Hz frequency and about 300mA peak current. D1 & D2 are placed facing the car on the same line, a couple of centimeters apart, on a short breadboard strip fastened to the wall. D2 picks-up the infra-red beam generated by D1 and reflected by the surface placed in front of it. The signal is amplified by IC2A and peak detected by D4 & C4. Diode D3, with R5 & R6, compensates for the forward diode drop of D4. A DC voltage proportional to the distance of the reflecting object and D1 & D2 feeds the inverting inputs of three voltage comparators. These comparators switch on and off the LEDs, referring to voltages at their non-inverting inputs set by the voltage divider resistor chain R7-R10.
Circuit diagram:
Park-Aid Circuit Diagram
R1_____________10K 1/4W Resistor
R2,R5,R6,R9_____1K 1/4W Resistors
R3_____________33R 1/4W Resistor
R4,R11__________1M 1/4W Resistors
R7______________4K7 1/4W Resistor
R8______________1K5 1/4W Resistor
R10,R12-R14_____1K 1/4W Resistors
C1,C4___________1µF 63V Electrolytic or Polyester Capacitors
C2_____________47pF 63V Ceramic Capacitor
C3,C5_________100µF 25V Electrolytic Capacitors
D1_____________Infra-red LED
D2_____________Infra-red Photo Diode (see Notes)
D3,D4________1N4148 75V 150mA Diodes
D5-7___________LEDs (Any color and size)
IC1_____________555 Timer IC
IC2___________LM324 Low Power Quad Op-amp
IC3____________7812 12V 1A Positive voltage regulator IC
Circuit modification:
A circuit modification featuring an audible alert instead of the visual one is available here: Park-Aid Modification
  • Power supply must be regulated (hence the use of IC3) for precise reference voltages. The circuit can be fed by a commercial wall plug-in adapter, having a DC output voltage in the range 12-24V.
  • Current drawing: LEDs off 40mA; all LEDs on 60mA @ 12V DC supply.
  • The infra-red Photo Diode D2, should be of the type incorporating an optical sunlight filter: these components appear in black plastic cases. Some of them resemble TO92 transistors: in this case, please note that the sensitive surface is the curved, not the flat one.
  • Avoid sun or artificial light hitting directly D1 & D2.
  • If your car has black bumpers, you can line-up the infra-red diodes with the (mostly white) license or number plate.
  • It is wiser to place all the circuitry near the infra-red LEDs in a small box. The 3 signaling LEDs can be placed far from the main box at an height making them well visible by the car driver.
  • The best setup is obtained bringing D2 nearer to D1 (without a reflecting object) until D5 illuminates; then moving it a bit until D5 is clearly off. Usually D1-D2 optimum distance lies in the range 1.5-3 cm.
  • If you are needing a simpler circuit of this kind driving a LED or a relay, click Infra-red Level Detector
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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:
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:
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
  • 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
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
  • 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:
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:
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:
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:

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.

  • 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)
  • 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 :
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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
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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