Tuesday, March 29, 2011

SCR Overvoltage Protection

Most good bench power supplies include a form of overvoltage protection, but for those power supplies or for other applications where over voltage protection is required, a simple over voltage crowbar circuit can be built. It uses just four components: a silicon controlled rectifier or SCR, a zener diode, a resistor and a capacitor.

SCR Overvoltage Protection Circuit

The SCR over voltage crowbar or protection circuit is connected between the output of the power supply and ground. The zener diode voltage is chosen to be slightly above that of the output rail. Typically a 5 volt rail may run with a 6.2 volt zener diode. When the zener diode voltage is reached, current will flow through the zener and trigger the silicon controlled rectifier or thyristor. This will then provide a short circuit to ground, thereby protecting the circuitry that is being supplied form any damage.

However it is necessary to ensure that the power supply has some form of current limiting. Often a fuse is ideal because the SCR will be able to clamp the voltage for long enough for it to blow. The small resistor, often around 100 ohms from the gate of the thyristor or SCR to ground is required so that the zener can supply a reasonable current when it turns on. It also clamps the gate voltage at ground potential until the zener turns on. The capacitor is present to ensure that short spikes to not trigger the circuit. Some optimisation may be required in choosing the correct value although 0.1 microfarads is a good starting point.
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CD4066 - Water Level Indicator With Alarm

This circuit is used to indicate the amount of water present in the overhead tank. Not only that, but this circuit also gives an alarm when the tank is full. CD4066 is used to indicate the level of the water through LEDs.

CD4066 - Water Level Indicator With Alarm

The circuit uses the widely available CD4066, bilateral switch CMOS IC to indicate the water level through LEDs. When the water is empty the wires in the tank are open circuited and the 180K resistors pulls the switch low hence opening the switch and LEDs are OFF. As the water starts filling up, first the wire in the tank connected to S1 and the + supply are shorted by water. This closes the switch S1 and turns the LED1 ON.

As the water continues to fill the tank, the LEDs2 , 3 and 4 light up gradually. The no. of levels of indication can be increased to 8 if 2 CD4066 ICs are used in a similar fashion. When the water is full, the base of the transistor BC148 is pulled high by the water and this saturates the transistor, turning the buzzer ON. The SPST switch has to be opened to turn the buzzer OFF. Remember to turn the switch ON while pumping water otherwise the buzzer will not sound!
Detail download here

Op-Amp Voltmeter Circuit With LED Bar display

This is a volt meter circuit based on LM324 OpAmps chip. A bargraph generator is nothing more than a slack-handful of OpAmps, all thrown into a single chip. It is cheaper to use the LM324 and put in the few extra components needed.

Op-Amp Voltmeter Circuit With LED Bar display

M324 OpAmp PinOut

R1 to R8 down the left all form a voltage divider from the 7.5v Zener diode. The resistors give me taps of 0.5v, 1.5v, 2.5v, 3.5v, 4,5v, 5.5v, and 6.5v. The top of the zener gives me the eighth voltage: 7.5v. These reference voltages are all connected to the negative-acting input of each OpAmp, and all the positive-acting inputs are gathered together for a common input. With 0v on the +ve inout, the output voltage of avery OpAmp is 0v.

If the input voltage lies between 0v and 0.5v then no LED lamps will light. If the input voltage rises to between 0.5v and 1.5v (1v +/-0.5v) then the first LED will light when the first OpAmp +ve input exceeds the -ve input threshold. In this way the LEDs all form a nice bar-graph display in 1v steps, +/- half a volt.

The A-B-C links should be in the A-B position for a normal bar-graph display, when each LED succesively lights as the voltage rises. With +4v input there will be four LEDs lit. If you fit the links in the A-C position then only one LED will light for each voltage step, to give a moving dot display. The top (last) link should always be in the A-B position for both modes.

This Op-Amp Voltmeter Circuit From www.sm0vpo.com:800

Detail download here

1.5V to 5VDC Converter by LT1073

If you want a 1.5V to 5V Step-Up Converter here is a simple circuit using LT1073 from Linear Technology. The LT1073 is a versatile micro-power DC / DC converter. The circuit requires few external components to deliver a fixed output of 5V.

1.5V to 5VDC Converter Circuit by LT1073

LT1073 Pinout

The very low minimum supply voltage of 1V allows the use of the LT1073 in applications Nowhere the primary power source is a single cell. An on-chip auxiliary gain block cans function as a low battery detector or linear post-regulator.The LT1073 is good idea, it Used for dc to dc converter.Average current drain of the LT1073-5 Used as shown in the Typical Application Circuit below is just 135mA unloaded, making it ideal for applications Nowhere Long battery life is Important. The circuit shown cans deliver 5V at 40mA from an input as low as 1.25V and 5V at 10mA from a 1V input.
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Thursday, March 24, 2011

Turn On Relay Delay for Power Amplifier

This is a circuit which built to one of my audio amplifier projects to control the speaker output relay. The purpose of this circuit is to control the relay which turns on the speaker output relay in the audio amplifier.

Turn On Relay Delay Circuit
Turn On Relay Delay Circuit for power amplifier

The idea of the circuit is wait around 5 seconds ofter the power up until the speakers are switched to the amplifier output to avoid annoying "thump" sound from the speakers. Another feature of this circuit is that is disconnects the speaker immediately when the power in the amplifier is cut off, so avoiding sometimes nasty sounds when you turn the equipments off.

This circuit is not the most accurate and elegant design, but it has worked nicely in my small home-built PA amplifier. This circuit can be also used in many other applications where a turn on delay of few seconds is needed. The delay time can be increased by using bigger C2 and decreased by using a smaller C2 value. Note that the delay is not very accurate because of simplicity of this circuit and large tolerance of typical electrolytic capacitors.
Detail download here

Voltage Indicator For 12V Power suplay

This circuit can clearly show the level of the supply voltage as long as the indicator has good 12 volts at its input, LED1 gives steady, uninterrupted yellow light. If the input voltage falls below 11 V, LED1 will start to blink and the blinking will just get slower and slower if the voltage drops further - giving very clear and intuitive representation of the supply's status. The blinking will stop and LED1 will finally go out at a little below 9 volts. On the other hand, if the input voltage rises to 13 V, LED2 will start to glow, getting at almost full power at 14 V. The characteristic voltages can be adjusted primarily by adjusting the values of R1 and R4. The base-emitter diode of T2 basically just stands in for a zener diode.

Voltage Indicator CircuitVoltage Indicator Circuit For 12V Power suplay

The emitter-collector path of T1 is inversely polarized and if the input voltage is high enough - T1 will cause oscillations and the frequency will be proportional to the input voltage. The relaxation oscillator ceases cycling when the input voltage gets so low that it no longer can cause breakdown along the emitter-collector path. Not all small NPN transistors show this kind of behavior when inversely polarized in a similar manner, but many do. BC337-40 can start oscillations at a relatively low voltage, other types generally require a volt or two more.
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12v Battery Monitor Circuit by LM339 Comparator

This is an interesting 12V Battery Monitor circuit of a low power electronic dc voltmeter circuit that can be used with car electric systems that run on 12 volt batteries.

12v Battery Monitor Circuit by LM339 Comparator

In the circuit having a voltage quad comparator (LM339) is used as a simple bar graph meter to indicate the state of charge 12-volt lead-acid battery acid. A 5 volt reference voltage is in each of the (+) inputs of four comparators and the (-) inputs are connected, each point is connected to a voltage divider. The LED lights up when the voltage at the negative (-)-input exceeds the reference voltage. Calibration can be by adjusting the 2K potentiometer so that all four LEDs illuminate when the battery voltage is 12.7 volts indicates a full charge with no load on the battery is done. At 11.7 volts, the LED should be made, and shows an empty battery. Each LED is a change of about 25% charge or 300 millivolts, so that 3 LEDs indicate 75%, 2 LEDs indicate 50%, etc.
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Mosfet Dimmer Circuit for Halogen lamp

A light dimmer circuit is a means of controlling the "brightness" level of a lamp, in this circuit we will use a 555 timer to control the brightness level of a low voltage incandescent bulb of up to 60 watts.

Mosfet Dimmer Circuit Mosfet Dimmer Circuit for Halogen lamp

The circuit works by pulse-width modulating the 12V supply to the lamp. The 555 timer is configured as a "variable cycle", astable oscillator running some where around 300 Hz.

Potentiometer 47K from minimum to maximum varies the values accordingly the duty cycle of the 555 timer controlling light dimmer circuit.

The power mosfet used here would be a TO-220 type such as MTP3055E or similar. Note the need for a TO-220 type heat sink for full rated loads.
Detail download here

Thursday, March 17, 2011

ON/OFF LED Fade Effect Circuit by Op-Amp LM324

The simple and easy to build on/off LED fade effect circuits included here will specially interest the new electronic hobbyists. Just like the name of the circuit, the light intensity of LEDs in this circuit will fade from high intensity to low intensity and then off.
On/off LED Fade Effect CircuitON/OFF LED Fade Effect Circuit by Op-Amp LM324

C 30 uF and R 100k (blue color) control the speed of the fading. You can replace the 100K ohm resistor with 100k linear potentiometer so you can adjust the speed any time. You can make the circuit even simplier by leaving out other of the transistors and those leds that are connected to it. Good for power led pulsing etc.
Op-Amp LM324 Pinout

LM324 is an OP-Amp amplifier. There 4 op amp, and we just use 2 op amp in above circuit diagram. You may use the other 2 op-amp to build another similar circuit. Transistor is BC547 and the led is ultra bright red with 220 ohm resistor in series.
Detail download here

1.5V LED Flasher Circuit by LM3909

This is a very simple 1.5V LED Flasher circuit based LM3909. It is known that LM3909 is an oscillator, a monolithic one, which is designed to flash Light Emitting Diodes (LED). According to the datasheet, it may deliver pulses of 2 more volts while operating on a supply of 1.5V by using the timing capacitor.
1.5V LED Flasher Circuit 1.5V LED Flasher Circuit by LM3909

The LM3909 features low cost, low voltage and low current drain, with a bright-high current LED pulse and wide temperature range. It can be applied on applications such as flashlight finder, siren for toy fire engine, sawtooth generators, emergency locators, warning indicators and etc.

List Component of 1.5V LED Flasher
LED1    : Red LED
C1 : 100uf/16V
IC1 : LM3909
Battery_:_____1.5V AAA
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NAND Gate Pulse Generator Circuit

The Following diagram is the Pulse (Clock) Generator circuit diagram of the which the build based on NAND Gate Logic IC. You May use IC 7400 or 4011 for this circuit. This circuit is very useful while checking / operating counters, stepping relays and other digital circuits. It avoids the procedure of setting a switch for the required number of pulses.

NAND Gate Pulse Generator CircuitNAND Gate Pulse Generator Circuit

7400 NAND Gate Pinout

For a range of Pulse speeds determined by a large capacitor (4.7 μF) and a logarithmicpotentiometer (1 MΩ), but feel free to play around and find Some better combinations for yourself. A single clock cans Also be Used to drive installments sequencers, so u cans have all the instruments to play together.
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Treble Booster Circuit by LM741

The following diagram is the circuit diagram of Treble Booster. This circuit can be used with an electric guitar (and also electronic instruments) to boost the higher order harmonics and give a more brilliant sound.
Treble Booster Circuit by LM741Treble Booster Circuit

A circuit of this type gives a fairly flat response at bass and most middle audio frequencies, with the upper-middle and lower treble frequencies being given a substantial amount of boost. In this circuit has can to improve the treble about 10000 Hz that 40 dB. By you can change C1 be other value as a result.

Detail download here

Fire Alarm Circuit by Thermistor

Here is a simple fire alarm circuit based NE555 timer and use thermistor as temperature sensor. This sensor will activate the alarm when the temperature is in high value.

In this fire alarm circuit, a thermistor works as the heat sensor. When temperature increases, its resistance decreases, and vice versa. At normal temperature, the resistance of the thermistor is approximately 10 kilo-ohms, which reduces to a few ohms as the temperature increases beyond 100°C. This phenomenon is employed here for sensing the fire.
Fire Alarm Circuit by ThermistorSimple Fire Alarm Circuit

The NE555 is configured as a free running oscillator at audio frequency. The transistors T1 and T2 drive IC1. The output of IC1 is couples to base of transistor SL100, which drives the speaker to generate alarm sound. The frequency of NE555 depends on the values of resistances R5 and R6 and capacitance C2. When thermistor becomes hot, it gives a low-resistance path for the positive voltage to the base of transistor T1 through diode D1 and resistance R2.
Detail download here

Saturday, March 12, 2011

Simple Photodiode Alarm

This photodiode alarm circuit can be used to give a warning alarm when someone passes through a protected area. The circuit is kept standby through a laser beam or IR beam focused on to the Photodiode. When the beam path breaks, alarm will be triggered.

Simple Photodiode Alarm Circuit Photodiode Alarm Circuit

Simple IR transmitter circuit

The circuit uses a PN Photodiode in the reverse bias mode to detect light intensity. In the presence of Laser / IR rays, the Photodiode conducts and provides base bias to T1. The NPN transistor T1 conducts and takes the reset pin 4 of IC1 to ground potential. IC1 is wired as an Astable oscillator using the components R3, VR1 and C3. The Astable operates only when its resent pin becomes high. When the Laser / IR beam breaks, current thorough the Photodiode ceases and T1 turns off. The collector voltage of T1 then goes high and enables IC1. The output pulses from IC1 drives the speaker and alarm tone will be generated.

A IR transmitter circuit is given which uses Continuous IR rays. The transmitter can emit IR rays up to 5 meters if the IR LEDs are enclosed in black tubes.

This circuit from http://electroschematics.com
Detail download here

Simple Pulse Generator Circuit by CD4049 Cmos Inverting IC

Here is Simple Pulse Generator circuit Based IC invertig CD4049. This circuit use only 1 active component and very..very few passives components around. It use digital cmos CD4049 Hex Inverting Buffer IC. The pulse generators can also produce a 50% duty cycle square wave. It may use digital techniques

 Pulse Generator circuit  by CD4049 Simple Pulse Generator circuit

CD4049 Pinout

  • The Pulse Rate frequency signal (F) = 1 /(1.4RC) .
  • The power supply used DC 5V-12Volt.
Detail download here

60 Hz Clock Pulse Generator Circuit By MM5369

Here is a 60 Hz clock pulse generator circuit provides a clean, stable square wave and it will operate on anywhere from 6 to 15 volts. The IC and color-burst crystal are the kind used in TV receivers. The 3.58 MHz output makes a handy marker signal for shortwave bands.

60 Hz clock pulse generator circuit60 Hz clock pulse generator circuit By MM5369

Resistor R1 is necessary to bias the inverter for class A amplifier operation. Capacitors C1 and C2 in series provide the parallel load capacitance required for precise tuning of the quartz crystal.

The Tuner Output is a buffered output at the crystal oscillator frequency. This output is provided so that the crystal frequency can be obtained without disturbing the crystal oscillator. The Divide Output is the input frequency divided by the mask programmed number. Both outputs are push-pull outputs
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1Hz Pulse Generator Circuit by IC 555

This is a 1Hz pulse generator circuit using the timer IC 555 which is wired as an Astable Multivibrator. The output pulses can be indicated visually by the LED. An Astable Multivibrator, often called a free-running Multivibrator, is a rectangular-wave generating circuit. This circuit does not require any external trigger to change the state of the output, hence the name free-running. This circuit can be used in applications that require clock pulses

1Hz Pulse Generator Circuit by IC 555 1Hz Pulse Generator Circuit

We can set the 555 to work at the desired frequency by selecting the right combination of resistances & capacitance.

Frequency = 1.44 / {(R1 + 2R2) * C1}
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Saturday, March 5, 2011

NE555 Lamp Dimmer Circuit

Here is a 12 volt lamp dimmer circuit that can be used to dim a standard 25 watt automobile brake or backup bulb by controlling the duty cycle of a astable 555 timer oscillator.
NE555  Lamp Dimmer  Circuit

When the wiper of the potentiometer is at the uppermost position, the capacitor will charge quickly through both 1K resistors and the diode, producing a short positive interval and long negative interval which dims the lamp to near darkness. When the potentiometer wiper is at the lowermost position, the capacitor will charge through both 1K resistors and the 50K potentiometer and discharge through the lower 1K resistor, producing a long positive interval and short negative interval which brightens the lamp to near full intensity. The duty cycle of the 200 Hz square wave can be varied from approximately 5% to 95%. The two circuits below illustrate connecting the lamp to either the positive or negative side of the supply.
Detail download here