555 Timer Circuits and Projects

CircuitsToday is listing some simple 555 timer circuits that have already been published in our site before. To know about the basics of NE 555 along with the timer circuit schematic, click on the links below.

555 Timer Circuit Schematic and Working Principle

555 Timer Monostable Circuit

555 Timer Oscillator Circuit

555 as an Astable Multivibrator

LM 555 Datasheet

From the articles above you will also get the idea about its duty cycle and also other 555 timer applications. Here are the links of some easy 555 IC circuits with complete description and circuit diagram. A small description is given for each link to give you a small idea about the circuit.

1. 7-Segment Counter Circuit

This timer circuit is wired as an astable multivibrator to display a seven segment counter with the help of the counter IC CD 4033. This circuit is mostly added on to other circuits so as to make it more attractive by displaying a counter. The timer circuit is used to trigger the counter IC, which in turn advances each count on the seven segment LED display LT543. The complete details about the circuit and its circuit diagram are given in the original article.

2. Flasher Circuit using NE 555

A 555 LED Flasher circuit uses an astable multivibrator which produces pulses for flashing the lamp. Two resistors are set in the circuit to control the flashing rate. A half-wave rectifier, a transistor, and a TRIAC is used to drive the load. The circuit shown in the original post had some mistakes and the modified circuit is also shown right below the original post. Also take a look at the special notes as you are testing the circuit in live, and may cause potential shock hazards.

3. Photo Switch Circuit

This circuit uses a relay and a sensor to sense and switch when the light intensity crosses a certain limit. A Light Dependent Resistor is used as the sensor. The timer is connected to two transistors to drive the relay. Take a look at the complete working of the circuit in the original link given above. Also read the special notes given in the article to ensure that the procedures followed to make the circuit work are done correctly.

4. InfraRed (IR) Sensor/Detector

This circuit has applications as a proximity detector or liquid level detector. It operates by detecting the distance from the target by reflection of an infra-red beam. The timer output is designed for a duty cycle of 0.8 milliseconds, with a frequency of 120 Hertz and 300 milliampere peak current. Such a timer drives the infrared LED. An LM 358 IC is also used in the circuit as a comparator so that it receives the signal from one diode, as soon as it gets the infrared signal from another diode, and passes it on to the inverting input of the IC. The detailed idea of the circuit can be obtained from the main article.

5. Remote Controlled Switch Circuit

This circuit is used to switch on and off an electrical appliance using a TV remote. The signals are sensed using a sensor IC called TSOP 1738. The IC output will be high when it is not disturbed by any signal.  This makes the transistor in the OFF state. If a signal with a frequency of about 38 Kilohertz falls on the IC, its output becomes low. This causes the transistor to conduct and thus sends a negative pulse to the timer IC, designed to act as a monostable multivibrator. Take a look at the circuit diagram and the detailed working on the main article.

6. Sensitive Intruder Alarm Circuit

The circuit is used to produce an alarm as soon as an intruder passes nearby the circuit. It can be setup on your home premises for safety reasons. The circuit uses a LDR to sense the change in light due to the reflection of the intruder. This output is given to an op-amp comparator circuit.

7. Infrared Motion Detector Circuit

An astable multivibrator circuit is designed with the help of a timer IC and an infrared diode is used to produce infrared beams which are sensed by a phototransistor as soon as it is cut due to the motion of an intruder.

8. Rain Alarm Circuit

This circuit is used to produce an alarm as soon as rain starts to pour in. The main components of the circuit are two transistors and a timer IC. A sensor is used to sense the fall of rain water and its output is given to a switch and thus to two transistors.

9. Missing Pulse Detector Circuit Using NE555

This circuit is used to find a missing pulse or abnormally long period between two consecutive pulses in a train of pulses. Such circuits can be used to detect the intermittent firing of the spark plug of an automobile or to monitor the heart beat of a sick patient.

10. Mobile Incoming Call Indicator

This circuit can be used to escape from the disturbance caused due to mobile phone rings when you are at home. All you have to do is place the circuit near your mobile phone, and it will give you a visual indication even if the ringer is deactivated.

11. Musical Horn Circuit

Two 555 timer IC’s are combined to produce a musical horn. The output of the first IC is connected to the discharge pin of the second IC. Both of them are connected to work as astable multivibrators.

12. 10 Minute Timer Circuit

This circuit is used to make an alarm to wake you after ten minutes. Here, the circuit uses an LED instead of a buzzer. The circuit can be modified in your own way. The circuit consists of only a timer circuit designed as a monostable multivibrator.

13. Brightness Controller for Low Power Lamps

This circuit helps you to reduce and increase the brightness of low power incandescent lamps. The timer IC is designed as an astable multivibrator with variable duty cycle. A transistor is also used whose input will be driven by the timer circuit. The output of the transistor drives the lamp. The duty cycle of the multivibrator can be changed with the help of a potentiometer.

14. Flashing LED Unit

A 555 LED Flasher circuit is used to produce a rotating effect when the LEDs are arranged properly. The circuit has very low current consumption and can be operated from even 3V button cells. An astable multivibrator circuit is set with the help of the timer IC with a duty cycle of 50% and 4Hz frequency. Another timer IC is also used to work as a trigger pulse inverter.

15. Ding-Dong Sound Generator

The cicuit consists of two SE 555 timers that is toggled between two frequencies to produce a ding-dong sound. The first one is connected to the second in such a way that the frequency of the second NE555 IC is modulated by the output from the first IC.

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Op-amp Circuits

Op-amp

CircuitsToday.com is listing some of the best op-amp circuits present in our sites. There are more than 20 circuits which show the different applications of the op-amp. We are listing the links of our best 15 circuits with detailed descriptions and circuit diagrams. Do not forget to go through the comments section for each post, from where you will get ideas about how to modify the circuit. Also if you have any doubts, feel free to ask them through comments.

Before going into detail about the different op-amp application circuits, it is important to know about the basics of op-amp, and the small applications of the IC. To learn about it click on the link – Operational Amplifiers (Op-amps)

The above linked article contains all the basics of op-amps, with the basic op-amp circuit with two transistors. The different advantages of op-amps are also specified, along with links to different basic op-amp circuits like Comparator Circuit, Schmitt Trigger Circuit, Astable Multivibrator, Monostable Multivibrator, Zero-crossing detector, voltage splitter and so on. The article also contains information about the 741 IC, its packaging style, the use of op-amp as an inverting and non-inverting circuit, and so on. The different pin assignments of the 741 IC are also explained with neat figures.

Given below are some links to some of the best op-amp based circuits designed by us. Most of them are simple and easy to make a home. We have given a very detailed description and circuit diagram for every one of the.

1.  Sensitive Intruder Alarm Circuit

In this circuit, apart from the 741 op-amp IC, a Light Dependent Resistor (LDR) is also used. The main use of the LDR is to sense the presence of a person through his shadow falling on the sensor. As soon as the shadow falls on it, the resistance of the device begins to increase. A 555 timer IC is also used to be triggered by a transistor and thus to drive the alarm load. Read more about the working of the circuit from the link above.

2. Transistor Amplifier Circuit-12 Watts

This circuit is very simple and inexpensive. Only one uA741 op-amp and four transistors are required for the working of this circuit. The op-amp produces the gain required and the transistors are connected to work as the speaker driver. The circuit is highly stable and is also known to produce a reasonable output of 12 Watts on a 4 Ohm speaker.

3. Sound Operated Flip Flop

This circuit is used to toggle the output pins status of a flip-flop IC, using a sound. The op-amp used here is the IC LM324. Two op-amps from the chip are selected and are used to amplify the sound picked by the condenser microphone. The third op-amp inside the IC is used as a level detector. The flip-flop IC used here is the IC CD4027.

4. Sound Pressure Meter

The op-amp used here is called CA 3140. The op-amp is connected as a non-inverting amplifier, and can be easily setup as a sound level checker at homes and theatres. You will find it very useful in checking the sound pressure of each channel on different positions of the room.

5. Infrared Motion Detector Circuit

This circuit is used to produce an alarm as soon as an intruder walks across the infrared rays produced by an IR diode. A 555 timer IC is also used here to work as an astable multivibrator. The beams produced by the IR diode are received by a photo-transistor. When an intruder walks by, the LM 1458 op-amp senses the difference in phase and automatically goes high.

6. Passive Tone Control Circuit

The circuit uses op-amp as the only active element, whereas all the other components are passive elements. Thus, the circuit got its name as Passive Tone Control Circuit. The circuit is divided into two parts – the op-amp based pre-amplifier and the Baxandall tone control circuitry. The op-amp used here is the TL072 IC. The Baxandall circuit principles and the whole circuit is explained in detail in the original article. This circuit does have some disadvantages like energy wastage, and high distortion.

7. Active Crossover Circuit

This circuit can be considered just the opposite of the passive tone control circuit. All the drawbacks that the passive circuit has is rectified by this circuit. They are known to be more suitable for HiFi audio systems. The circuit divides the complex audio signal into two bands, one being the low frequency signal, and the other being the low frequency signal. These two signals are further amplified separately and is bi-amped to its corresponding low frequency and high frequency bands. The op-amp used here is the LM833 IC, which is basically a dual op-amp that is designed for audio purposes.

8. Car Subwoofer Filter

This circuit finds a lot of applications in the use of automobile subwoofers. The circuit is basically a low pass filter whose pass frequency lies between 60 hertz and 160 hertz. The op-amp used in this circuit is called the TL072 dual BIFET op-amp IC. The chip has two op-amps. One of them is connected as a buffer, and the other is connected as a low-pass filter.

9. Low-pass Filter for Subwoofer

The IC used here is the TL062 IC. It is basically a dual high input impedance JFET op-amp. It is known for its good audio characteristics. The circuit description and diagram is available in the main article. 3-Input Microphone Preamplifier

The op-amp used here is the IC LM348, due to its unique properties like high gain, internally compensated quad-operational amplifier with a class AB output stage, low input supply drain current, and so on. The IC is to be powered with the help of a dual power supply. Four of them are used in this circuit.

10. 3-Way Active Crossover Network

This circuit finds wide applications in audio amplifier systems. The op-amp used here is called LF353 IC, which was developed by National Semiconductors. The IC is a dual JFET op-amp internally compensated input offset voltage.  The op-amp is also known for its low offset currents, high bandwidth, and low input bias currents due to the JFET based input stage. Two of them are used in this circuit. One of them is used to buffer the input audio signal, and the other is used to handle the three bands of the audio namely bass, mid-range, and treble. To know more about the circuit, click on the link above.

11. Audio Line Driver

In this circuit, an op-amp called TSH22 IC, developed by ST Microelectronics is used. At a high level of modulation, and with a bandwidth of 25 Mega Hertz, the IC is known to drive medium impedance loads with low distortion and high output current.

12. Subwoofer Filter

The circuit diagram of a subwoofer filter with the help of op-amps is given in the article above along with a detailed description. The circuit consists of 10 op-amps. The circuit needs a low pass filter with a cut-off frequency of 200 hertz, as the audio frequencies below the value are known to be in the subwoofer range. The circuit may look a little complex, but after reading the working of the circuit, you will find that it is quite simple. A potentiometer is also required to couple one of the inverting inputs of the op-amp. You can use an LED if needed, and it is optional.

13. Preamplifier for Dynamic Microphones

This circuit is known to be a low noise pre-amplifier suitable for dynamic microphones. The op-amp used here is called uA739, manufactured by Fairchild Semiconductors. Such an op-amp is known to be famous for its high gain and excellent stability. The IC package contains two op-amps, but only one of them is used for the circuit.

A capacitor is also used in the circuit to provide DC de-coupling.  The audio signals from the microphone are coupled to the non-inverting input of the op-amp. A resistor-capacitor network is also connected in the circuit. This network helps in bypassing the unwanted high frequency signals that comes from the microphone. This circuit is highly applicable in audio circuits as it can handle a wide range of signals. To learn more about the circuit, click on the link above.

14. 3 Input Mic Mixer Circuit

In this circuit, 4 op-amp 741 IC’s are used. Out of them three of them are designed to work as pre-amplifiers and the fourth is connected as a summing amplifier, which adds the signals from the output of the three pre-amplifiers. The three pre-amplifiers produce a gain of about 40dB to the individual input signals. The summing amplifier produces a gain of about 5dB to the final output signal. Thus the total gain of the circuit comes around 45dB.

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Hobby Electronics Circuits and Projects

For all electronic hobbyists out there, CircuitsToday is listing some of our own hobby electronic circuits for you. Most of these circuits have been tested by us. You can bring in your own modifications to the circuit. For beginners, these electronic hobby projects may be a little difficult. You can feel free to comment below and ask whatever you want to know. We will help you with whatever information we can provide. Click on the link of each heading given in the list below, to go to the main content. Do not forget to check out the comments as well, to get a better idea of the electronic hobby circuits.

1.       Dark Detector Circuit

This hobby circuit is used to produce an alarm as soon as the light inside a room goes off. The main components used are a basic 555 timer IC and Light Dependent Resistor (LDR), and an output buzzer alarm. The output of the sensor is given to the NE 555 IC. When there is proper light inside a room, the resistance of the sensor will be very low. As soon as the light goes off, the resistance begins to increase. This in turn triggers the IC which is connected to the alarm, and thus produces an output sound. This type of hobby projects can be easily modified to switch other electrical components by using a relay and a transistor to be connected to the output of the 555 timer instead of the buzzer alarm.

2.       Musical Car Reverse Horn Circuit

This interesting circuit is used to make a musical horn as soon as you put your car in reverse gear. This type of hobby electronics projects works with the help of two integrated circuits. One is a simple 7805 voltage regulator IC that is used to minimize the car battery voltage to 5 volts. A further drop to 3.6 Volts is needed and this is given by two diodes. This voltage is given to the second IC, called the UM66. This IC is known to be a music generator. When the car is put in reverse gear, the switch becomes on and the circuit gets connected to the car battery. This causes the UM 66 to produce a music tone. This tone can be further amplified by connecting a transistor driver from the output of the IC to the loudspeaker. The hobby circuit diagram can be seen in the main post given above.

3.       Dancing Light

The hobby circuit diagram of the circuit is given in the original post. This circuit uses an astable multivibrator using a 555 timer IC. The clock pulses from the timer are given to an IC called CD4017. The output of the IC becomes high alternatively. Thus, the LED’s also turn on alternatively, giving it a dancing feel. You can customize the speed of the LED glow by changing the frequency of the clock pulses generated by the timer IC.

4.      Jet Engine Sound Generator

Hobby circuits such as these can be made with the help of the sound generator IC HT2844P. The IC is designed to produce four different sounds of a jet engine like the missile sound, machine gun sound, high speed sound and low speed sound. Each sound is assigned its respective IC number. You just have to connect the associated pins to the ground by using the respective push button switches. You can also connect an LED to the circuit as an indicator to show that the sound has been activated. The hobby schematics can be obtained from the original post given in the link above.

5.       Whistle to Beep Circuit

The circuit consists of a CMOS Hex inverter IC which helps in producing a small beeping sound, whenever you make a whistle. The beeping sound will last for about 3 seconds. There are altogether 6 inverters in the IC. One of them is connected to an audio amplifier that amplifies the signal packed by the microphone. Another inverter of the IC is connected as a Band Pass Filter (BPF) with a center frequency of about 2 kilohertz. The circuit also contains an astable multivibrator and a monostable multivibrator apart from the buzzer output. Check out the hobby circuit diagram show in the link above.

6.       Puff to OFF LED Circuit

A condenser mic is used as a sensor to sense a puff made by the user and thus make an LED switched OFF. Two transistors are connected as a latching pair, which drives the LED to glow. The LED remains ON as long as the puff is given to the mic. The mic converts the sound pressure into an electrical signal and is amplified by a transistor. The output of the transistor drives the LED to the OFF state. A switch must also be given to turn the LED back t its glowing position.

7.       Touch Switch Circuit Diagram Using NE 555 IC

The circuit consists of a small touch plate controller using the 555 timer IC. Hobbyists can easily design this circuit for various applications like doorbells, buzzers, toys, and so on. The circuit mainly consists of a relay that operated for a preset time and then turns off immediately as soon as anything touches the touch plate. A transistor is also used to drive the relay, which can be used to drive loads like bell, lights or motor.

8.       Automobile Turn Signal Circuit

Electronics enthusiasts may find this circuit very interesting. The main objective of the circuit is to provide sequential signal light in automobiles. Two main IC’s are used in this circuit – a TS 555 CN CMOS timer IC and a CD4017 decade counter IC. The CMOS IC is connected as an astable multivibrator so as to trigger the other one. When the CD4017 IC is triggered, the output will go high and low in sequence and the speed of the sequencing will be proportional to the triggering frequency. Four transistors are also provided to drive the corresponding Light Emitting Diodes (LED). Check out the comments on the post as well to know more about the modifications that can be brought to the circuit.

9.       Parking Sensor Circuit

This circuit can be practised on your car for sensing the distance between the rear bumper of the car and any obstacle behind the car. The distance can be understood from the combination of the LEDs used in the circuit.  The 555 timer is used as an astable multivibrator in the circuit. This timer drives the infrared diode that is connected in the circuit to emit infrared pulses. The operating frequency of the transmitter is around 120 Hertz. Take a look at the circuit diagram to know more about it. A detailed explanation is also given in the post above.

10.     Electronic Toss Circuit

A timer IC is used as an astable multivibrator here at a frequency of 10 hertz, along with a 74LS76 dual JK flip flop. The main objective of the circuit is to toss head or tail. The output of the timer is inverted using a transistor. The component details and the explanation is given in the post above.

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