At 50 years, the 555 timer IC defies conventional wisdom

You’re well aware of the IC shortage and its impact. Commentators and analysts have provided many explanations, including unexpectedly high demand, capacity limitations, Covid, and too much reliance on latest-process ICs. They also talk about floods and other disasters that have disrupted some major facilities as well as increased call for “legacy” analog-centric ICs, which can only be fabbed at smaller, older sites. Probably, there is no single primary cause, but instead smaller supply-chain ripples that are aligned in phase and add up to a major issue.

So, I’ll add my reason to the list: the wide use of the 555 timer IC. “What’s that?” you’d ask. “How’s that possible?”

I’ll tell you how. This IC has been on the market and in wide use since it was introduced in 1972. In IC technology chronicles, that’s the days of dinosaurs. This largely unchanged IC has been in production for that long and is still available from about a dozen vendors. I can’t find specific numbers, but I suspect many millions are still used in both legacy and new designs every year. So maybe it’s time to retire the 555 and make room in those legacy fab queues for other, newer analog ICs?

Of course, I’m only kidding. The 555, with the deceptively simple description of “Timer” on its datasheets, can be configured for monostable (timing) or astable (oscillation) modes. It’s a wonderful 8-pin device, using just 28 internal transistors in analog mode (Figure 1). It doesn’t do much by itself, but it can be made to do so many things when enhanced with few passive external components. And with active ones, it can do even more. It’s been a remarkable device for hobbyists and professionals alike.

Figure 1 The block diagram of the 555 timer IC is simple, but its applications are varied and numerous. Source: Texas Instruments

For hobbyists, the 555 has been a valuable entry point and platform for experimenting with electronics and seeing the imaginative way building-block components can be configured to do so many things. Since it’s a low-frequency and bipolar device, it doesn’t have critical layout considerations, while its pin functions can be observed with a low-end oscilloscope or even a voltmeter (yes, they can). For professionals, it has been a planned-in-advance, low-cost solution to a headache-inducing design requirement, or the solution to an “oh-oh, we have a problem here” fix-it late in the design or in the field.

555 timer history

I won’t recount the history of the 555 timers as it has been covered extensively elsewhere. The best source is the oral history provided by Hans Camenzind himself, who, while working solo under a freelance contract for Signetics, created the 555. He conceived of, designed, laid out, cut the rubylith masking-film masters, and tested it (don’t know what rubylith is? look it up!). You can see the original datasheet here. Although he passed away in 2012, his legacy truly lives on via his oral-history interview with a transcript posted here. Camenzind also wrote a fascinating article, “Redesigning the old 555,” published in IEEE Spectrum in September 1997.

If you’re not familiar with the 555 or know a budding engineer who might want to do some good hands-on analog-circuit projects, there are many clever Design Ideas about it posted on EDN. Also, check out the “555 Cookbook” by Walt Jung, the classic compendium of 555 circuit and applications ideas. Even better, you can literally get into the 555 by getting the Discrete 555 Timer kit from Evil Mad Scientist, which uses discrete transistors and passive components (Figure 2).

Figure 2 If you want to probe within the 555, this emulation kit makes it possible. It uses only discrete active and passive components to let you observe all of its internal points. Source: Evil Mad Scientist

Still alive and well

Conventional wisdom is that ICs don’t have a long new-product design-in life. As with so much of such presumed “wisdom,“ it is both true and not-so-true. Certainly, many advanced digital ICs have a viable life of just three, five, or perhaps a few more years, and then they are no longer preferred for new designs. On the other hand, a good analog IC, whether a basic op-amp or perhaps a DC/DC converter, maybe a new-design candidate for 10 or more years.

There are several reasons for this. One is that vendors like it, as the engineering and up-front costs are paid for and the margins can be very high. At the same time, the subtleties of the analog process are all resolved, so yields are high, which is good for both the vendor and the user.

Moreover, many system designers like to manage their risks in a new product, and while they may need to use the latest digital IC, they don’t necessarily want to change everything in a new design. Therefore, by continuing to use an established, fully-understood analog IC, they minimize their overall risks by taking some uncertainty out of the project. That makes a lot of sense.

The fact that this IC has turned 50, has been used on NASA space missions, is still widely designed-in, and is the result of the efforts of one person working mostly alone tells a worthwhile story. I wonder if any of the media outlets that cover celebrities and milestones will pick up on this story. Don’t worry, I am not holding my breath for that to happen, as the story lacks the “splash” and celebrity elements that the media craves. That’s too bad in many ways, as it’s a story worth telling.

Have you recently relied on the 555 in a new design? Or have you used it to solve a problem that came up late in the design cycle? Was the use of the 555 accepted at the design review or ridiculed?

Related Content

Pin Configuration, Modes & Its Applications

The IC 555 timer was invented by “Signetic Corporation” and it was termed as SE or NE555 timer. Generally, it is a monolithic timing circuit that gives precise and highly stable delays of time or oscillation. These types of ICs are very cheap and reliable in cost when we compared with the OP-Amp applications in the same areas. These ICs are used as an astable and monostable multivibrators in digital logic probes, DC-DC converters, tachometers, analog frequency meters, voltage regulators, temperature controlled and measurement devices. The IC SE555 is used for where the temperature ranges from – 55°C to 125°C and the IC NE555 is used for where the temperature ranges from 0° to 70°C.

What is a 555 Timer IC?

The IC 555 timer is a one type of chip used in different applications like an oscillator, pulse generation, timer. The designing of IC 555 timers can be done by using various electrical and electronic components like transistors, resistors, diodes and a flip flop. The operating range of this IC ranges from 4.5V -15V DC supply. The functional parts of the 555 timer IC include flip-flop, voltage divider and a comparator. The main function of this IC is to generate an accurate timing pulse. In the monostable mode, the delay of this IC is controlled by the external components like a resistor and capacitor. In the astable mode, both the duty cycle & frequency are controlled by two external resistors and one capacitor.

555 Timer IC Pin Configuration

The 555 timer IC consist of 8-pins where each pin has some function. The pin configuration of this IC is shown below.

GND Pin

Pin-1 is a GND pin which is used to supply a zero voltage to the IC.

Trigger Pin

Pin-2 is a trigger pin which is used to convert the FF from set to RST (reset). The output of the timer depends on the amplitude of the external trigger pulse that is applied to the trigger pin.

Output Pin

Pin-3 is an output pin.

Reset Pin

Pin-4 is a RST pin. When the negative pulse is applied to this pin to disable or reset, and false triggering can be neglected by connecting to VCC.

Control Voltage Pin

Pin-5 is the control voltage pin used to control the pulse width of the output waveform and also the levels of threshold and trigger. When an external voltage is applied to this pin, then the output waveform will be modulated

Threshold Pin

Pin-6 is the threshold pin, when the voltage is applied to threshold pin, then it contrasts with a reference voltage. The set state of the FF can be depends on the amplitude of this pin.

Discharge Pin

Pin-7 is the discharge pin, when the output of the open collector discharges a capacitor between the intervals, then it toggles the output from high to low.

Supply Terminal

Pin-8 is the voltage supply pin which is used to supply the voltage to the IC with respect to the ground terminal.

Operating Modes of 555 Timer IC

The operating modes of a 555 timer are astable, bistable and monostable. Each mode of operation signifies with a circuit diagram and its output.

Astable Mode Operation

In this mode, the circuit of the IC 555 timer produces the continuous pulses with exact frequency based on the value of the two resistors and capacitors. Here the charging and discharging of the capacitors depends on a specific voltage. The circuit diagram of the 555 timer in astable mode is shown below. If the voltage is applied to the below circuit, the capacitors continuously gets charged through two resistors and generates pulses continuously. In the following circuit pins 2 & 6 are shorted together for endless re-activate the circuit. If the o/p trigger pulse is high, then capacitor in the circuit totally discharges. Long time delays are accomplished by using the higher values of the resistors and capacitors.

Monostable Mode Operation

In this mode, the circuit generates only single pulse when the timer gets an indication from i/p of the trigger button. Pulse duration can be depends on the values of the resistor and capacitor If an activating pulse is applied to the i/p of the circuit through a push button, then the capacitor gets charge and the timer circuit extends a high pulse, then it remains high until capacitor totally discharges. If it is necessary to enhance the time delay, then higher rate of capacitor and resistor are required.

Bistable Mode Operation

In this mode, the circuit produces 2-stable state signals which are low and states. The o/p signals of low and high state signals are controlled by reset & activate the i/p pins, not by the charging & discharging of capacitors. If a low logic signal is given to active pin, then the o/p of the IC circuit goes to high level. If the low logic signal is given to the RST pin, then the o/p of the circuit goes to low level.

Important Features of the 555 Timer

555 timer IC works from a wide range of power supplies ranging from +5V to +18V.

Sourcing or sinking load current is 200mA.

The external components must be selected correctly, so that the timing intervals can be completed in several minutes along with the frequencies beyond several hundred kHz.

The o/p of a 555 timer IC can drive TTl due to its high current o/p.

It takes a temperature stability of 50 ppm/oC change in temperature (ppm means parts per million)

The timer’s duty cycle is adjustable.

The max power dissipation per package is 600 milliwatts & its reset and trigger i/ps has logic compatibility.

555 Timer Circuits

The 555 timer ICs are used to generate a precise square wave form and that is used in many circuits. This circuit is designed with transistors, diodes, resistors and flip flops, and this circuit can be worked in the range of 4.5-15V DC supply. The 555 timer circuit consists of three functional parts, namely flip-flops, a comparator and a voltage divider.

The main function of the comparator is to compare 2-i/p voltage levels such as inverting (-) and non-inverting (+) terminals. If the ‘V’ is high at the non inverting terminal, then the o/p is high. The /p resistance of perfect comparator is infinite.

As the i/p resistance is endless in the comparator, the voltage between all the 3-resistors are similarly divided and the value across each resistor is Vin/3

Flip/flops are digital electronic devices and it has a memory. If the i/p is high while low at R, then the o/p at Q is high. When S is high, o/p of the Q is also high & if R is high, then the o/p of the Q is low.

555 Timer IC based Projects for Engineering Students

The 555 timer IC is used in many electronic engineering projects to generate a pulse signal. Here we have discussed some major 555 timer IC based projects and these are very useful for engineering students.

Low-High Voltage DC Converter using IC 555

This project is used to develop the voltage nearly double to the i/p voltage using the voltage multiplier principle. For example, If the input voltage is around 5V DC, then the o/p we can get is around 10V DC. This project is designed with 555 timer, it operates in astable mode. In this project, the capacitors are connected in series and to charge these capacitors IC 555 timer delivers the clock pulses. This charged capacitors change the voltage which is nearly equal to the double the i/p voltage. The o/p can be calculated by using the multimeter.

Wire Loop Breaking Alarm Signal for Burglars

This project is used to identify when the thief attacks to break the window glass act to give an alarm. This project is designed with a 555 timer IC and this project is used as a security system. When the wire loop breaks, then the IC activates the buzzer to give an alert for indication.

Hidden Active Cell Phone Detector

This project is designed to identify any activated mobile phone from one and half feet distance to avoid the use of unauthorized cell phone in prohibited areas or defense security. This project is designed with 555 timer IC which operates in monostable mode. When any unknown person tries to make a call then the buzzer will give a signal presence of an active cell phone.

Touch Controlled Load Switch

This project is designed to regulate a load for the short time duration by using a touch sensitive switch and a 555 timer IC. This IC operates in monostable mode and activates by a touch plate that is connected to its trigger pin. The o/p of the IC provides logic high for a fixed time interval which is decided by the RC time constant. The o/p makes a relay to switch ON the load for that duration after that it switches OFF automatically.

Please refer to this link to know more about Distance Relay.

Please refer to this link for 555 IC Timer MCQs

Thus, this is all about 555 timer IC basics, pin description and operating modes. We hope that you have got a better understanding of this concept . Furthermore¸any queries regarding this concept or engineering project ideas, please give your valuable suggestions by commenting in the comment section below. Here is a question for you, what is the main function of a 555 timer IC?

12 Awesome Projects and Circuits with IC 555 Timer

So, “What can you do with a 555 timer?” In which projects and circuits 555 timer can be used? If you have just started experimenting with IC 555 timer or even if you are an experienced electronic hobbyist, this question must have come to your mind.

The IC 555 Timer can be used in projects such as delay generator, adjustable ON/OFF timers, pwm generators, function generator etc. Common 555 timer circuits are – motion detector, smoke detector, proximity sensors, IR transmitter, clap switches, LED blinkers, rain alarm, fire and burglar alarm etc.

As 555 Timer needs very few components to function properly, it can be used extensively in hobby electronics. Here is a list of some of the applications of this popular timer IC.

1. Simple Alarm using 555 Timer

This is a Simple Alarm circuit using 555 Timer. In this circuit 555 timer runs in astable multivibrator mode and produces a running square wave output. This output is then fed into the speaker using an electrolytic capacitor in series. This circuit can also be used as an burglar alarm or as an rain alarm with little modifications.

To know more about it please visit the Project Page.

Simple Alarm Circuit

2. Sense of Time Tester

The Sense of Timer Tester is an interesting application of IC 555 Timer. As the name suggests, you can test how quick your response time is? Basically, here the IC 555 is used as an astable multivibrator.

In the circuit the LED blinks for 0.1 second and then remains off for about 1.5 seconds. And, if you are able to press the switch at the same instant when the LED is glowing, then the LED will remain ON and you win the game.

You need to press the switch as soon as you see the LED glowing. Sounds easy – not that much, since the average human reaction time is about 3 seconds.

So, you will not be able to catch the LED that is blinking so fast just by observing it. (Hint : you have to get into the rhythm of blinking LED and press the switch by your intution.)

Thus, it’s quite a challenge for you to catch the blinking LED and it takes a bit of practise. On the whole, It’s a fun game to play with your family.

To know more about it visit the Project Page.

Sense of Time Tester

3. Adjustable On/Off Timer

The basic functionality of the 555 timer is to work as a reliable and accurate timer. And this Adjustable ON/OFF timer circuit using 555 timer, just do that.

It can provide a time delay from 16 minutes upto 9 hours. As we know that for longer time delays (longer than 20 minutes), the IC 555 timer does not perform well.

So, to make it more reliable, we need to combine it with two decade counters (IC 4017). As a result, we get an reliable 16 minutes to 9 hours timer.

In addition, this circuit’s design is modular. So that you can add even more 4017 IC’s in the chain to get the extra longer time delays.

Also, the output of 555 timer is capable of driving a relay directly. Which enables it to control electrical appliances working on AC.

This circuit can be used for various applications such as (i) Electric Soft-start (ii) Conveyor Belt Sequence (iii) Flash Control (iv) Furnace Safety Purge Control etc.

To know more about it please visit the Project Page.

Adjustable ON-OFF Timer

4. Automatic Street Light using 555 Timer

It is a small project using 555 timer. The idea is basically to use 555 timer to switch ON/OFF street light automatically. This circuit makes use of a special kind of resistor known as LDR (Light Dependent Resistance). The LDR is used here to sense light and darkness.

The LDR enables 555 Timer to switch ON/OFF light according to light conditions. In this circuit, 555 timer IC is used as a Flip-Flop.

To know more about it visit the Project Page.

Automatic Street Light using 555 Timer

5. Variable Frequency Generator using IC 555

This circuit is very useful for electronic hobbyists. Using this circuit you can easily generate frequencies ranging from few Hz to several kHz. It is basically an astable multivibrator circuit using 555 timer. Its frequency can be adjusted by an 100 K potentiometer (variable resistor).

The common uses of these type of circuits include, signal driving for motor drive and other pulse control related circuits.

And, since the output (frequency) generated is in the range of audio frequencies. It can be easily used to troubleshoot audio devices.

To know more about it please visit the Project Page.

Adjustable Frequency Circuit

6. 555 Timer Relay Circuit

If you want to control electrical appliances through IC 555 Timer, you will going to need this circuit. This timer IC can easily be connected to a relay (also known as electrically operated switches).

The Relay is a device used to control electrical appliances working on mains AC by a smaller voltage DC (4.5 V to 24V). The output of IC 555 Timer can be connected directly to a relay.

By using this circuit you can easily automate home appliances such as a fountain pump, LED lights, fans etc. It is a very practical circuit to be used in day-to-day life.

To know more about it visit the Project Page.

555 Timer Relay Circuit

7. Blinking LED Flasher Circuit

The Blinking LED Flasher Circuit is a tiny circuit build with 555 timer. It can work on just two AA or AAA battery pack. You can build this circuit and fit it in a matchbox (with AAA battery). The LED remains ON for 10% of the timer period and OFF for 90% of the time.

This circuit can also be used as an LED chaser circuit in which two parallel string of LED can be turned OFF and ON alternatively.

The practical uses of LED Flasher circuit includes – vehicle turn indicator or emergency stop light for a vehicle, as a “Don’t Disturb Sign” and “Emergency Exit” indicator.

To know more about it please visit the Project Page.

Blinking LED Flasher Circuit

8. Square Wave Generator

The Square wave generator is a circuit that generates a series of square wave pulses. These types of circuits are frequency used in electronics and particularly in signal processing. Using IC 555 Timer we can make a very simple square wave generator circuit with minimal components. The 555 timer in this circuit works as an astable multivibrator mode.

Square wave circuits are extensively used in digital electronics for clock and timing control signals. Since all logical circuits utilizes square waveforms on their input and output gates.

The output of 555 timer can be directly used with other logic circuits. In fact, one of the most basic applications of 555 timer is as an pulse generator.

To know more about it please visit the Project Page.

Square Wave Generator

9. Touch to On Switch with 555 timer

This is an interesting application circuit utilizing IC 555 Timer. This project is based on the fact that the trigger terminal of 555 timer is very sensitive. And it can be triggered simply by touching it with your fingers. Once triggered, it switches on for a set period of time and then switches itself back to OFF state.

In fact, IC 555 Timer is very suitable to make a touch sensitive switch.

This can also switch ON an LED or an LED bulb working on AC mains with the use of an Relay. This circuit works as an monostable multivibrator.

This simple project has many versatile applications. Some of them are, shockproof switches for bathroom, touch operated door-bells and buzzers etc.

To know more about it visit the Project Page.

Touch to on Switch with 555 Timer

10. 5 Minute Timer Circuit

This circuit will switch ON an LED for about 5 minutes and then switch it completely OFF. It is a typical monostable multivibrator circuit using IC 555 timer. The Timing capacitor sets the time delay period. On Pressing the Trigger switch, the output of 555 timer goes HIGH for approx. 5 minutes and then goes LOW.

To know more about it please visit the Project Page.

5 Minute Timer Circuit

11. 5 Minute Delayed On Timer Circuit

This circuit will work similar to the circuit shown in the 5 minute ON timer. But it will provide a delay of 5 minutes before switching ON the electrical or electronic device. In this circuit, the output is taken from the Vcc and the “output” pin 3 as suggested in the circuit diagram.

Also, to further extend the circuit, you can connect a relay (with back emf protection) to the output of 555 timer. And this modification enables it to control electric device such as an LED light bulb or a fan.

To know more about it please visit the Project Page.

5 Minute Delayed Timer Circuit

12. PWM Circuit using 555 Timer

This is a simple PWM (pulse width modulation) circuit using 555 timer for controlling smaller loads. Instead of using resistors in series with an LED or small motor which wastes a lot of power. The PWM signal provides an average voltage across the load without any resistors. It is an very efficient way to deliver power for smaller loads.

Its application areas includes digital electronics where a single microcontroller is used to control various electronic devices. Also, this circuit can also work as a pulse generator.

To know more about it please visit the Project Page.

5 Minute Timer Circuit

13. Long Duration Timer using IC 555 Circuit

As the name suggests, this is a long duration timer circuit using IC 555 Timer. The timer can be set to provide a time period from 30 minutes upto 50 Hours.

The advantage of this particular long duration timer is that it doesn’t use a variable resistor to set the time interval. Instead in this circuit, we used two decade counters – IC 4017 to provide accurate longer time delay.

This 555 timer circuit comes handy when you are planning a holiday tour. There may be some electrical appliances such as outdoor lights that need to be switch on during the night time.

Also if you have a fish tank at home then it will have some equipments such as lights and auto-feeder etc. Now these appliances need to be switched ON/OFF at a particular time on a daily basis or once in every two days.

In such situations, this timer circuit is a must have. It can be set to automatically switch ON/OFF electronic or electrical appliance at a particular time period.

To know more about it please visit the Project Page.

Long Duration Timer Circuit using 555 Timer

In case you are interested in more IC 555 Timer projects. Below is a good video demonstrating how IC 555 timer can be used in various projects.

More IC 555 Timer Projects and Circuits

Summary

This tiny 555 timer IC is designed with a lot of hobby applications in mind. It can work from a range of voltages and tolerate variations in temperatures.

These advantages enable it to be seemlessly integrated in a variety of useful circuits such as timers and delay timers. It can be used as square wave and pulse generators, in Automatic lights, frequency generators and many more different types of electronic circuits.

Also, it becomes very handy when it is used as a long duration timer. You can use it while you are out of your home for holidays.

You can have a peace of mind while rock-climbing or rafting on water that this tiny piece of electronics (that you can fit on your nail) is taking care of your pets and home.