Voltage Limiter for Guitar Amplifiers

Guitar amplifiers using output devices such as the TDA7293 (100 W) or LM3886 (68 W) are surprisingly of ten damaged as a result of excessive supply voltage in the quiescent state. The transformers are of ten used so close to their specification that this problem can even be caused by a high mains input voltage. In most countries the domestic AC outlet voltage is permitted to rise as high 10 % above the nominal (published) value. Since replacing the transformer is not an attractive proposition, the author developed a relatively simple electronic solution to the overvoltage problem: a voltage limiter for the symmetric supply to the amplifier.
The circuit is based on the classical voltage regulator arrangement of a Zener diode connected to the base of a pass transistor. However, in this version we replace the conventional bipolar transistor with a power MOSFET.The circuit is symmetrical with respect to the negative and positive supplies, and so we shall only describe the positive half.
Voltage Limiter for Guitar Amplifiers Circuit Diagram

The input voltage (at most 50 V) supplies the chain of Zener diodes D1, D2 and D3 via resistor R3. The resistor limits the current through the Zener diodes to about 5 mA. The series connection of Zener diodes has the advantage that their dissipation is divided among them, as well as giving more options for the total voltage drop by judicious selection of individual components. The sum of the diode voltages (39 V with the values given) must be greater than the desired limiting out-put voltage by the gate-source voltage of the MOSFET. C1 smooths the voltage across the Zener diode chain. The circuit therefore not only limits the voltage, but also reduces the ripple (hum component) on the supply. The gate of the HEXFET is driven via R1. In con-junction with C4, this prevents the FET from oscillating.
Without any load the output voltage is rather higher than expected. With a small load, such as that presented by the output stage in its quiescent state, it falls to the desired value. The circuit then does not provide regulation of the output voltage, but rather a stabilisation function.The operation of the negative half of the circuit is identical to that of the positive half apart from the polarity of the voltages, and hence a P-channel MOSFE T must be used there.
It is worth noting that there is a relatively large degree of variation (up to a few volts) in the gate-source voltage of the HE XFETs used. This can be compensated for by selecting the Zener diodes in the chain and the cur-rent through them, but for most applications the exact voltage at which limiting begins to occur will not be critical.
The HEXFETs must be provided with adequate cooling. If possible, they can be attached to the heatsink already present in the amplifier; other wise, a separate heatsink will be required. A thermal rating of 2.5 K/W will be suitable.

Author :Alfred Rosenkränze - Copyright: Elektor

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Electronic Car Horn

An LM556 dual oscillator/timer, U1, configured as a two-tone oscillator drives U2, a dual 4-watt amplifier. One of the oscillators, pins 1 to 6, contained in U1 produces the upper frequency signal of about 200 Hz, while the second oscillator, pins 8 to 13, provides the lower frequency signal of about 140Hz.

Electronic Car Horn Circuit Diagram

Increase or decrease the frequencies by changing the values of C2 and C3. U1's outputs, pins 9 and 5, are connected to separate potentiometers to provide control over volume and balance. Each half of U2 produces 4W of audio that is delivered to two 8 ohms loudspeakers via capacitors C7 and C8.

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Automatic Wiper Control

A continuously working wiper is a big problem when it is raining slightly.The wiper control given here makes the wiper to sweep at rates from 1S to 10 S.

The circuit is build around an astable multivibrator using NE 555.Here the output at pin 3 remains high for a time period set by R2 ,and low for a time period set by R3.The low output pulse drives the transistor pair to drive the wiper motor to make one sweeping cycle and waits for next low pulse to arrive for next sweep.The high going pulse at pin 3 determines how many time should wiper should sweep in a given period of time.

Automatic Wiper Control Circuit Diagram:

Notes:

• Connect the circuit to 12V line from Vehicle and connect the wiper motor and wiper switch as shown in figure.
• For setting the device first find out how much time it is required for the wiper to complete one sweep cycle.Now adjust
• R3 such that wiper makes correct one sweep cycle.Fix R2 some where on the dash board.And now the system is ready to use.
• You can adjust the sweep rate of the wiper using R2 according to the intensity of rain.

Source : Circuits today

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Low Cost Garage Stop Light

A novel use of solar cells makes positioning your car in the garage rather easier than old tyres, a mirror, or a chalk mark.The six solar cells in figure 1 serve as power supply and as proximity sensor. They are commercially available at relative low cost. The voltage developed across potentiometer Pi is mainly dependent on the intensity of the light falling onto the cells. The circuit is only actuated when the main beam of one of the car's headlights shines direct onto the cells from a distance of about 200 mm (8 inches). The distance can be varied somewhat with P,
Low Cost Garage Stop Light Circuit Diagram :

Under those conditions, the voltage developed across C1 is about 3 V, which is sufficient to trigger relaxation oscillator Ni. The BC547B is then switched on via buffer N2 so that D3 begins to lfash. Diodes Di and D2 provide an additional in-crease in the threshold of the circuit. The total voltage drop of 1.2 V across them ensures that the potential at pin I of the 4093 is always 1.2 V below the voltage developed by the solar cells. As the trip level of Ni lies at about 50 per cent of the supply voltage, the oscillator will only start when the supply voltage is higher than 2.4 V.
The circuit, including the solar cells, is best constructed on a small veroboard as shown in figure 3, and then fitted in a translucent or transparent manmade fibre case. The case is fitted onto the garage wall in a position where one of the car's headlights shines direct onto it. The LED is fitted onto the same wall, but a little higher so that it is in easy view of the driver of the car. When you drive into the garage, you must, of course, remember to switch on the main beam of your headlights!

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Car Alarm Sound Booster

For car alarms, emphasis should be put on hearing the audible alert and identifying it as belonging to your ‘wheels’. Unfortunately, modern car alarm systems seem to have more or less the same alarm sound especially if they are from the same brand. Also, to comply with legal noise restrictions, the alarm sound is not always loud enough to be heard if the car is parked down the road.

The circuit shown here is designed to help boost the alarm sound by also activating the car’s horn(s) when the alarm goes off.Internally the car alarm system often provides a signal that activates the (optional) engine immobilizer and/or volume (ultrasound) sensors. This signal usually goes Low upon system triggering and high again when the alarm system is deactivated.

Car Alarm Sound Booster Circuit Diagram :

The alarm activation signal is fed to the circuit through D1. When in idle state, T1’s gate is High and consequently the FET conducts, keeping power FET T2 firmly switched of f. When the system gets an active low signal, T1 switches of f allowing timing capacitor C2 to charge via R2. About 15 seconds later, when the voltage across C2 is high enough, T2 starts to conduct and relay RE1 is energized. This, in turn, provides the required path for the ‘lights flashing’ signal to energize RE2 and feed battery power to the car’s horn(s).

When the alarm system is turned off the activation signal returns to High. T1 starts to con-duct and rapidly discharges C2 via R3. T2 is then cut off and RE1 is de-energized. Diode D2 suppresses back EMF from RE1.The circuit draws less than 2 mA when idling. When activated the circuit’s current consumption is virtually that of the RE1 coil.RE1 is any simple SPST or SPDT relay, capable of switching about 0.5 A (at 12 V). The coil rating is for 12 VDC and a current requirement as low as you can find. Fuse F1 should be a slow blow type and rated about twice RE1’s coil current.

The BS170 in position T2 can sink a continuous current of about 0.5 A. However, a value of 1.2 A pulsed is specified by Fairchild for their devices. To keep the FET’s d-s current due to C2 discharging within safe limits, R2 may be increased, C2 decreased and R3 increased, all proportionally. A factor of 2 will keep the FET out of harm’s way with maybe a slight change in the 15-second delay and the sensitivity of the circuit.C1 is used as a smoothing capacitor and F2 should be rated in accordance with the horn(s) maximum current draw.

Caution.The installation and use of this circuit may be subject to legal restrictions in your country, state or area.

Author : Hagay Ben-Elie - Copyright : Elektor

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Automotive Ignition Coil Buzz Box

 

Automotive Ignition Coil Buzz Box Circuit Diagram :

 

This picture is a circuit for a buzz coil using a standard car battery to create. Dual timer IC 556 is used to set the frequency and the duty cycle of the coil current to be determined. One of the timer is used as an oscillator for generating the rectangular waveform 200 Hz to control (IRF740 MOSFET), while the second timer is stopped and the oscillator switching points are opened and closed (closed = a). The result is a steady stream of sparks of the ignition coil a distance of about 5 milliseconds, while the switching points are closed. Operation: Pin 8 and 12 the trigger inputs, and a timer which are driven by the points and an inverted signal of the clock output (pin 9) to produce.

When the pin 9 is grounded points high, and vice versa. The signal on pin 9 controls the reset line (pin 4) of the second timer and keeps the output at pin 5 is low, while pin 4 and pin 8 is low and 12 high (still open). The 15K and 47K resistors and capacitors are 0.33uF synchronization components that the frequency and duty cycle of the second clock, which is about 4 milliseconds to 2 milliseconds apart to secure positive and negative. During the time interval is positive, the doors are always high MOSFET causing the coil to the current height of about 4 amps.

This equates to approximately 80 milli joules of energy in the coil is released in the spark plug when the clock output (pin 5) moves on the ground, turn off the MOSFET. A zener diode 12 volts is placed on the node 10 and 27 ohms for the MOSFET gate input is above or below 12 volts -0.7 volts. A Zener diode 200 volts / 5 W used for the drain voltage of the MOSFET 200 and limit the useful life of the spark to expand. The circuit must operate reliably with a jumper, but the circuit operation with no load applied (the son of candle down, etc.) may cause a malfunction, because most of the energy absorbed by the Zener. You can also use a transient voltage suppressor (TVS) as 1.5KE300A 1.5KE200A or instead of the zener. This is probably a good hand, but difficult to obtain.

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Car's Brake Lights Monitor Circuit

The circuit described below monitors your car's brake lights, and indicates by a light emiting diode 12V whether they both function correctly. In that sense, it can save you money by preventing your being fined for driving with defective brake lights, and it also leads to increasing road safety.

Car's Brake Lights Monitor Circuit Diagram :

The monitor depends inevitably on the voltage drop across the supply lines to the two lamps. For the circuit to work correctly, that drop needs to be greater  than 0.6 V. If this is not so, the drop must be in- creased by adding a 5 V diode in series with each  lamp. Transistor Ti and T2 in figure 1 form a  Schmitt trigger, which reacts to the voltage drop  across the supply lines to the two brake lights. This  reaction manifests itself in Di lighting via T3. If  one of the brake lights is faulty, the switch-on cur- rent drawn by the other lamp will cause Di to light  briefly when the brake pedal is pressed. If both  brake lights are defective, Di will not light at all. All three possible states of the brake lights are thus indicated. sitivity of the circuit, can be adjusted within narrow limits with Pi. The preset is best adjusted with one lamp out of action in a manner which makes Di light briefly as described above.

If you find it disturbing that Di lights every time you brake, the operation can be reversed by replacing the BC557B in the T3 position by a BC547B  (n-p-n). The collector of T3 is then connected to the  positive supply line, and the emitter to R6. On the  printed circuit board this means that the flat edge  of T3 must be turned the other way. A second base  connection has also been provided on the PCB.

Note, however, that this configuration no longer makes it possible to ascertain whether one or both brake lights are faulty, i.e., when the LED lights, one or both lamps need replacing.

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Simple 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 (refer Fig. 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.

Circuit diagram :

 

Fig. 1: Car reverse horn Circuit Diagram

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. 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.

The flasher circuit (shown in Fig. 2) is built around timer NE555, which is wired as an astable multivibrator 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.

Fig. 2: Flasher Circuit Diagram

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 headlight. 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 : EFY

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Simple Garage Stop Light Circuit

A novel use of solar cells makes positioning your car in the garage rather easier than old tyres, a mirror, or a chalk mark. The six solar cells in figure 1 serve as power supply and as proximity sensor. They are commercially available at relative low cost. The voltage developed across potentiometer Pi is mainly dependent on the intensity of the light falling onto the cells. The circuit is only actuated when the main beam of one of the car's headlights shines direct onto the cells from a distance of about 200 mm (8 inches). The distance can be varied somewhat with P,

Simple Garage Stop Light Circuit Diagram :

 

Under those conditions, the voltage developed across C1 is about 3 V, which is sufficient to trigger relaxation oscillator Ni. The BC547B is then switched on via buffer N2 so that D3 begins to  lfash. Diodes Di and D2 provide an additional in- crease in the threshold of the circuit. The total voltage drop of 1.2 V across them ensures that the  potential at pin I of the 4093 is always 1.2 V below the voltage developed by the solar cells. As the trip  level of Ni lies at about 50 per cent of the supply  voltage, the oscillator will only start when the supply voltage is higher than 2.4 V.

The circuit, including the solar cells, is best constructed on a small veroboard as shown in figure 3, and then fitted in a translucent or transparent man- made fibre case. The case is fitted onto the garage wall in a position where one of the car's headlights shines direct onto it. The LED is fitted onto the same wall, but a little higher so that it is in easy view of the driver of the car. When you drive into the garage, you must, of course, remember to switch on the main beam of your headlights!

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Brake Lights Monitor

The circuit described below monitors your car's  brake lights, and indicates by a light emiting diode  whether they both function correctly. In that sense, it can save you money by preventing your being fined for driving with defective brake lights, and it also leads to increasing road safety.

Circuit diagram :

Brake Lights Monitor Circuit Diagram

The monitor depends inevitably on the voltage drop across the supply lines to the two lamps. For the circuit to work correctly, that drop needs to be greater than 0.6 V. If this is not so, the drop must be increased by adding a 5 V diode in series with each lamp. Transistor Ti and T2 in figure 1 form a  Schmitt trigger, which reacts to the voltage drop across the supply lines to the two brake lights. This reaction manifests itself in Di lighting via T3. If  one of the brake lights is faulty, the switch-on cur- rent drawn by the other lamp will cause Di to light  briefly when the brake pedal is pressed. If both  brake lights are defective, Di will not light at all.  All three possible states of the brake lights are thus  indicated.

The hysteresis of the trigger, and, therefore, the sensitivity of the circuit, can be adjusted within narrow limits with Pi. The preset is best adjusted with one lamp out of action in a manner which makes Di light briefly as described above.

If you find it disturbing that Di lights every time  you brake, the operation can be reversed by replacing the BC557B in the T3 position by a BC547B  (n-p-n). The collector of T3 is then connected to the positive supply line, and the emitter to R6. On the printed circuit board this means that the flat edge  of T3 must be turned the other way. A second base  connection has also been provided on the PCB.  Note, however, that this configuration no longer makes it possible to ascertain whether one or both brake lights are faulty, i.e., when the LED lights, one or both lamps need replacing.

The printed circuit board is not available ready  made. In figure 1, Si is the brake pedal switch, and Lai and La2 are the brake lights.

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Car Cigar Lighter to USB Power Socket Circuit

Nowadays, almost all computer systems have logic blocks for working with a USB port. A USB port, in practice, is capable of supplying more than 100 mA of continuous electric current at 5V to the peripherals which are hooked up with the bus. So a USB port could be utilized, without having any problems, for powering 5V DC operated tiny electronic devices.

Today, a lot of handheld gadgets (for example, portable reading lamps) utilise this resource of the USB port to recharge their built-in battery pack using the support of an internal circuitry. Typically 5V DC, 100mA electric current is needed to satisfy the input electrical power demand.

The above diagram shows the circuit of a versatile USB power socket that properly converts the 12V battery voltage into stable 5V. This circuit can make it possible to power / recharge any USB power-operated device, working with in-dash board cigar lighter socket of the car.

 

The DC supply presented from the cigar lighter socket is fed to an adjustable, three-pin regulator LM317L (IC1).

 

Capacitor C1 buffers any disorder in the input supply. Resistors R1 and R2 regulate the output of IC1 to constant 5V, that is accessible at the ‘A’ type female USB socket. Red LED1 signifies the output condition and zener diode ZD1 acts as a protector against excessive voltage.

Assemble the circuit on a general purpose PCB and enclose inside a slim plastic cabinet as well as the indicator and USB socket. Whilst wiring the USB outlet, make sure proper polarity of the supply. For interconnection between the cigar plug pin as well as the device, use a long coil cord as shown in second image.

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Car Anti-Theft Wireless Alarm

This FM radio-controlled anti-theft alarm can be used with any vehicle having 6- to 12-volt DC supply system. The mini VHF, FM transmitter is fitted in the vehicle at night when it is parked in the car porch or car park. The receiver unit with CXA1019, a single IC-based FM radio module, which is freely available in the market at reasonable rate, is kept inside.

Receiver is tuned to the transmitter's frequency. When the transmitter is on and the signals are being received by FM radio receiver, no hissing noise is available at the output of receiver. Thus transistor T2 (BC548) does not conduct. This results in the relay driver transistor T3 getting its forward base bias via 10k resistor R5 and the relay gets energised.

When an intruder tries to drive the car and takes it a few metres away from the car porch, the radio link between the car (transmitter) and alarm (receiver) is broken. As a result FM radio module gene-rates hissing noise. Hissing AC signals are coupled to relay switching circuit via audio transformer. These AC signals are rectified and filtered by diode D1 and capacitor C8, and the resulting positive DC voltage provides a forward bias to transistor T2.

Thus transistor T2 conducts, and it pulls the base of relay driver transistor T3 to ground level. The relay thus gets de-activated and the alarm connected via N/C contacts of relay is switched on. If, by chance, the intruder finds out about the wireless alarm and disconnects the transmitter from battery, still remote alarm remains activated because in the absence of signal, the receiver continues to produce hissing noise at its output. So the burglar alarm is fool-proof and highly reliable. (Ed: You may have some problem catching the thief, though, if he decides to run away with your vehicle_in spite of the alarm!)

Copyright : EFY

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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 (refer Fig. 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.

Circuit diagram :

Fig. 1: Car Reverse Horn Circuit Diagram

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. 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.

The flasher circuit (shown in Fig. 2) is built around timer NE555, which is wired as an astable multivibrator 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.

Circuit diagram :

Fig. 2: Flasher Circuit Diagram

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 headlight. 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 : EFY

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Simple but reliable car battery tester

This circuit uses the popular and easy to find LM3914 IC. This IC is very simple to drive, needs no voltage regulators (it has a built in voltage regulator) and can be powered from almost every source.

Circuit diagram :

Simple but reliable car battery tester Circuit Diagram

 

When the test button is pressed, the Car battery voltage is feed into a high impedance voltage divider. His purpose is to divide 12V to 1,25V (or lower values to lower values). This solution is better than letting the internal voltage regulator set the 12V sample voltage to be feed into the internal voltage divider simply because it cannot regulate 12V when the voltage drops lower (linear regulators only step down).

Simply wiring with no adjust, the regulator provides stable 1,25V which is fed into the precision internal resistor cascade to generate sample voltages for the internal comparators. Anyway the default setting let you to measure voltages between 8 and 12V but you can measure even from 0V to 12V setting the offset trimmer to 0 (but i think that under 9 volt your car would not start). There is a smoothing capacitor (4700uF 16V) it is used to adsorb EMF noise produced from the ignition coil if you are measuring the battery during the engine working. Diesel engines would not need it, but I'm not sure. If you like more a point graph rather than a bar graph simply disconnect pin 9 on the IC (MODE) from power.

For the first comparator the voltage is : 0,833 V corresponding to 8 V
* * * * * voltage is : 0,875 V corresponding to 8,4 V
for the last comparator the voltage is : 1,25 V corresponding to 12 V
Have fun, learn and don't let you car battery discharge... ;-)

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Car Central Locking System

For a few pounds you can buy a kit from any automotive accessory shop that will allow your car to be fitted with a central-locking door system. Such a kit essentially comprises a number of motors. There is also a control unit that enables the whole system to function. Here we show an example of such a unit. There are 5-wire motors and 2-wire motors. The 5-wire version is used in doors that have a key-lock.

 

There are 2 connections for the motor itself and 3 connections for the sensor part (an ‘open’ and a ‘close’ contact). These sensors determine whether the door is to be unlocked or locked. If there is no key lock in the door, these sensors are superfluous and a 2-wire motor can be used.

The polarity of the motor determines whether the locking mechanism goes up or down. By making a circuit that simply reverses the polarity of the motor, the door can be either locked or unlocked. The winding of the motor is connected between M1 and M2 in the schematic. When relay Re1 is energised, all motors will, for example, rotate anti-clockwise. By activating Re2 the motors will rotate clockwise. This depends on the actual polarity of the motor, of course.

The sensors are connected to R1 and R10. Here you have to pay careful attention. If Re1 causes the door to unlock, then Re1 has must obviously be connected to the ‘open’ contact. In that case, Re2 is for locking the doors and R10 is then connected to the ‘close’ contact. The R/C-combinations R16/C3 and R15/C4 ensure that the relays are energised for a certain amount of time (obviously this can be changed if this time is too short or too long for your doors).

Circuit diagram :

Car Central Locking System Circuit Diagram

This time has to be just long enough to lock or unlock the doors. The third wire of the sensors is the common and has to be connected to +12 V. The RC circuits at the inputs Sopen en Sclose ensure that the motors are driven only once when the door is locked or unlocked.  In addition, there is a provision to allow the unit to be connected to a car alarm. There are two types of alarm available, with positive or negative control. In order to make the unit universally applicable, both types of alarm can be used. The circuit around T3 and T4 makes this possible. The diode inputs (D3 and D8) react to a rising edge, R6 and R8 react to a falling edge. An RC time constant is used here as well to ensure that both relays are energised only once.

Maybe this is stating the obvious: a motor unit has to be built into each door. All motor wires and sensor wires are connected in parallel to the electronics. The actual type of relay is not critical. The type indicated has the following proper-ties: coil 12 V/400 Ω; max. switching current 12 A (AC), max. switching power 1200 VA.

PCB Layout :

Finally, a car is a hostile environment for electronics. Ensure good connections, use automotive connectors and crimp these on the wires using the appropriate crimping tool. Solder connections in wires are best avoided. They have the tendency to break where the wire transitions into the solder connection when the wire is subject to vibration. Fasten the wires at regu-lar intervals.

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Simple Car Alarm Sound Booster

For car alarms, emphasis should be put on hearing the audible alert and identifying it as belonging to your 'wheels'. Unfortunately, modern car alarm systems seem to have more or less the same alarm sound especially if they are from the same brand. Also, to comply with legal noise restrictions, the alarm sound is not always loud enough to be heard if the car is parked down the road.

Circuit diagram :

Simple Car Alarm Sound Booster Circuit Diagram

The circuit shown here is designed to help boost the alarm sound by also activating the car's horn(s) when the alarm goes off. lnternally the car alarm system often provides a signal that activates the (optional) engine immobilizer and/or volume (ultrasound) sensors. This signal usually goes Low upon sys-tem triggering and high again when the alarm system is deactivated.

The alarm activation signal is fed to the circuit through Dl . When in idle state, T1 's gate is High and consequently the FET conducts,  keeping  power  FET T2 firmly switched off. When the  system gets an  active  low signal, T1  switches  off allowing  timing  capacitor C2 to charge  via  R2. About 15 seconds later, when the voltage across C2 is high enough, T2 starts to conduct and relay RE1 is energized. This, in turn, provides the required path for the 'lights flashing' signal to energize RE2 and feed battery power to the car's horn(s).

When the alarm system is turned off the activation signal returns to High. T1 starts to conduct and rapidly discharges C2 via R3. T2 is then cut off and REl is de-energized. Diode D2 suppresses back EMF from REl.

The circuit draws less than 2 mA when idling. When activated the circuit's current consumption is virtually that of the RE1 coil. RE1 is any simple SPST or SPDT relay, capable of switching  about 0.5 A (at 12 V). The coil rating is for 12 VDC and a current requirement as low as you can find. Fuse F1 should be a slow blow type and rated about twice RE1's coil current.

The B5.170 in position T2 can sink a continuous current of about 0.5  A. However, a value of 1.2 A pulsed is specified by Fairchild  for their devices. To keep the FET's d-s current due to C2 discharging within safe limits, R2 may be increased, C2 decreased and R3 increased, all proportionally. A factor of 2 will keep the FET out of harm's way with maybe a slight change in the 15-second delay and the sensitivity of the circuit. C1 is used as a smoothing capacitor and F2 should be rated in accordance with the horn(s) maximum current draw.

Caution. The installation and use of this circuit may be subject to legal restrictions in your country, state or area.

Author : Hagay Ben-Elie - Copyright : Elektor

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In-Car Food And Beverage Warmer

This is a very useful device for those who are frequently on the move. It will keep your tea, coffee or food warm while consuming little power.  The circuit is simple. The ubiquitous timer 555 is used as a free-running astable multivibrator. Diodes 1N4148 are connected in reverse direction to facilitate maximum variation of the duty cycles.

 

Power transistor T1 is Darlington type with 5A capacity and output of more than 60 watts. The chosen discrete components assure fixed frequency of 1 Hz (approximately) at pin 3 of timer IC1 (555). Resister R1 and potmeter VR1 (1-mega-ohm) allow adjustment of the duty cycle. The higher the duty cycle, the higher the output of the heater.

You can connect up to five 10W heating elements in parallel, totaling 50 watts. The consumption of current will be significantly less if fewer coil elements are connected in parallel through toggle switches S2 through S4. Each of these switches has a 6A rating.

Assemble the circuit on a general-purpose PCB. Mount power transistor TIP120 on a thick heat-sink. Isolate the circuit from the heating elements using only two wire connections. Use wires that can carry more than 6A current. Fix the coil elements below an aluminium or steel rectangular plate which is at least 1mm thick. Do not forget to insulate the heating plate from the elements. Use the car battery for the power supply with a proper current-carrying-capacity wire.

Author :Ashok K. Doctor - Copyright : EFY

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Car Head Lights Turn Off

This circuit when setup in a car automatically turns off the head light after a preset time after the ignition switch is turned off.So you can walk out easily from the dark garage in the light of your car.

Circuit diagram :

Car Head Lights Turn Off  Circuit Diagram

When the ignition switched on first the voltage from battery is fed to the relay through diode D1.When the ignition switch is turned off it produces a negative going pulse at the pin 2 that triggers the timer. The output of the IC goes high for the time set by R1  .This makes the transistor Q1 to conduct to energize the relay to drive the headlight.After the set time the light goes off.With the value of components used you can make a setting from 10 S to 60 S.

Notes :

• Assemble the circuit on a good quality PCB or common board.
• Fit the potentiometer on somewhere on the dashboard so that  you can easily set the timing.

Source :circuitstoday

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Automatic Bicycle Light

T his  automatic  bicycle  light  makes cycling in the dark much  easier (although you still need  to pedal of course). The circuit  takes  the  ambient  light  level  into account and only turns on  the light when it becomes dark.  The light is turned off when no  cycling has taken place for over  a minute or if it becomes light  again. The biggest advantage of  this circuit is that it has no manual controls. This way you can  never ‘forget’ to turn the light  on or off. This makes it ideal for  children and those of a forgetful  disposition.

 

Bicycle Light Image :

To detect when the bicycle is  used (in other words, when the  wheels turn), the circuit uses a  reed switch (S1), mounted on  the frame close to the wheel.  A small magnet is fixed to the  spokes (similar to that used with  most  bicycle  speedometers),  which  closes  the  reed  switch  once for every revolution of the  wheel. Whilst the wheel turns,  pulses are fed to the base of T1  via C1. This charges a small electrolytic capacitor (C2). When it is  dark enough and the LDR there-fore has a high resistance, T2  starts conducting and the lamp  is turned on. With every revolution of the wheel C2 is charged  up again. The charge in C2 ensures that T2  keeps conducting for about a minute after  the wheel stops turning. Almost any type of  light can be connected to the output of the  circuit.

 

Circuit diagram :

Automatic Bicycle Light Circuit Diagram

Part List :

Resistors
R1 = 1MΩ (SMD 0805)
R2,R4 = 100kΩ (SMD 0805)
R3,R6 = 1kΩ (SMD 0805)
R5 = LDR e.g. FW150 Conrad Electronics # 183547

Capacitors

C1 = 1µF 16V (SMD 0805)
C2 = 10µF 16V (SMD chip type)
C3 = 100nF (SMD 0805)

Semiconductors

T1 = BC807 (SMD SOT23)
T2 = STS6NF20V (SMD SO8)

Miscellaneous

S1 = reed switch (not on board) +
2-way right angle pinheader
BT1 = 3–12V (see text)

 

With a supply voltage of 3V the quiescent  current when the reed switch is open is just  0.14 μA. When the magnet happens to be in  a position such that S1 is closed,  the current is 3 μA. In either case  there is no problem using batteries to supply the circuit. The  supply voltage can be anywhere  from 3 to 12 V, depending on the  type of lamp that is connected. Since it is likely that the circuit  will be mounted inside a bicycle light it is important to keep  an eye on its dimensions. The  board has therefore been kept  very compact and use has been made of SMD components. Most  of them come in an 0805 pack-age.  C2 comes in a so called  chip version. The board is single sided with the top also acting as the solder side.

The print outline for the LDR (R5)  isn’t exactly the same as that of  the  outline  of  the  LDR  mentioned  in  the  component  list.  The outline is more a general one  because there is quite a variety  of different LDR packages on the  market. It is therefore possible  to use another type of LDR, if for  example the light threshold isn’t  quite right. The LDR may also be  mounted on the other side of the  board, but that depends on how  the board is mounted inside the  light. For the MOSFET there are also many alternatives available, such as the FDS6064N3 made  by   Fairchild ,  the  SI4864 DY  made by  Vishay Siliconix , the IR F74 0 4 made by IR F or the NTMS 4N01R 2G  made by ONSEMI. The reed switch also  comes in many different shapes and sizes; some of them are even waterproof and come with the wires already attached.

 

For the supply connection and  the connection to the lamp you  can either use PCB pins or solder the wires directly onto the  board. The soldered ends of the  pins can be shortened slightly so that they  don’t stick out from the bottom of the board.  This reduces the chance of shorts with any metal parts of the light. Do take care when you use a dynamo  to  power the circuit the alternating voltage must first be rectified! The same applies to  hub dynamos, which often also output an  alternating voltage.

 

Please Note. Bicycle lighting is subject to legal restrictions, traffic laws and, additionally in  some countries, type approval.

Download : 090102-1 PCB layout (.pdf), from www.elektor.com

Author : Ludwig Libertin (Austria) – Copyright : Elektor

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Motorbike Alarm

This simple to build alarm can be fitted in bikes to protect them from being stolen. The tiny circuit can be hidden anywhere, without any complicated wiring. Virtually, it suits all bikes as long as they have a battery. It doesn't drain out the battery though as the standby current is zero. The hidden switch S1 can be a small push-to-on switch, or a reed switch with magnet, or any other similar simple arrangement. The circuit is designed around a couple of low-voltage MOSFETs configured as monostable timers. Motorbike key S2 is an ignition switch, while switch S3 is a tilt switch. Motorbike key S2 provides power supply to the gate of MOSFET T2, when turned on.

When you turn ignition off using key S2, you have approximately 15 seconds to get off the bike; this function is performed by resistor R6 to discharge capacitor C3. Thereafter, if anyone attempts to get on the bike or move it, the alarm sounds for approximately15 seconds and also disconnects the ignition circuit. During parking, hidden switch S1 is normally open and does not allow triggering of mosfet T1. But when someone starts the motorbike through ignition switch S2, MOSFET T2 triggers through diode D1 and resistor R5. Relay RL1 (12V, 2C/O) energises to activate the alarm (built around IC1) as well as to disconnect the ignition coil from the circuit. Disconnection of the ignition coil prevents generation of spark from the spark plug. Usually, there is a wire running from the alternator to the ignition coil, which has to be routed through one of the N/C1 contacts of relay RL1 as shown in Fig.1 Fig.2 shows the pin configurations of SCR BT169, MOSFET BS170 and transistor BC548.

Circuit diagram :

 

 Motorbike Alarm Circuit Diagram

Motorbike Alarm-Pin Configurations :

 

Pin configurations of BT169, BS170 and BC548

Also, on disconnection of the coil, sound generator IC UM3561 (IC1) gets power supply through N/O2 contact of relay RL1. This drives the darlington pair built around T3 and T4 to produce the siren sound through loudspeaker LS1.  To start the vehicle, both hidden switch S1 and ignition key S2 should be switched on. Otherwise, the alarm will start sounding. Switching on S1 triggers SCR1, which, in turn, triggers MOSFET T1. MOSFET T1 is configured to disable MOSFET T2 from functioning. As a result, MOSFET T2 does not trigger and relay RL1 remains de-energised, alarm deactivated and ignition coil connected to the circuit.  Connection to the ignition coil helps in generation of spark from the spark plug. Keeping hidden switch S1 accessible only to the owner prevents the bike from pillaging. Tilt switch S3 prevents attempt to move the vehicle without starting it. Glass-and metal-bodied versions of the switch offer bounce-free switching and quick break action even when tilted slowly.

Unless otherwise stated, the angle by which the switch must be tilted to ensure the contact operation (operating angle), must be approximately 1.5 to 2 times the stated differential angle. The differential angle is the measure of the 'just closed' position to the 'just open' position. The tilt switch has characteristics like contacts make and break with vibration, return to the open state at rest, non-position sensitivity, inert gas and hermetic sealing for protection of contacts and tin-plated steel housing. If you find difficulty in getting the tilt switch, you may replace it with a reed switch (N/O) and a piece of magnet. The magnet and the reed switch should be mounted such that the contacts of the switch close when the bike stand is lifted up from rest.

EFY Note. Make sure that while driving, the two internal contacts of the Tilt switch don't touch each other.

 

Author : T.A. BABU - Copyright : electronicsforu

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