What is timer in electronics

Keyword: timer

Update: LMC555 and TLC555 (CMOS) compared with NE555 (BJT)

This electronics mini-course has been dealing with the differences between the modern CMOS version LMC555 and TLC555 and the old BJT version NE555 since 2009.

The purpose of this mini-course is to make electronics technicians aware of the significant advantages of the CMOS version. The electronics forums show that the old NE555 is still far too well known. There are only two known advantages of the NE555 compared to the LMC555 or TLC555: The significantly higher current carrying capacity of the output signal and the slightly higher maximum permissible operating voltage. With regard to higher current loads, it is usually worthwhile to use an inexpensive NPN transistor (BJT) or N-channel MOSFET and to use the advantages of the CMOS version of the 555 timer IC.

The cover picture announces it! This update is about a very specific matter. It's about the control input, which is used for pulse width modulation (PWM) or for the calibration of a precise duty cycle of 50% (square wave generator) or the pulse times (monoflop). More details can be found in other 555 mini-courses mentioned in this mini-course.

This control input is very often not required. Then, according to the manufacturer's instructions, this input should be blocked with a capacitor for the purpose of interference-free operation. Interference pulses on this line should be diverted to GND. It is strange that the manufacturers give very different capacitance values ​​between 1 nF and 100 nF. I dealt with this matter and have summarized it here as an update. This is indicated in the third part of the title picture. In the first part it is explained how the self-clocking and external clocking interference comes about and in the second part the situation is explained in more detail for the self-clocking interference and which additional measures are recommended, depending on the application and requirements. This content can be read in the new chapter "THE CONTROL INPUT AND THE BLOCK CAPACITOR Cc".

Greetings to you
ELKO Thomas

New 555, CMOS, timer

A brief introduction to the index page of my electronics mini-courses

My electronics mini-courses are mainly accessed using a search engine. The ease of finding is due to the high Google sensitivity of the electronics compendium (the ELKO) and this also applies to my electronics mini-courses.

If you always target electronics mini-courses in this way, it is easy to miss the header, even though every electronics mini-course contains the same header with the same informative links. This happens so easily because one is fixated on one topic. This post should refer to this header and also to the index page with the large overview of other electronics mini-courses, some of which also fit the interested topic. More about this and two special topics in this post here:

Greetings to you
ELKO Thomas

General555, LMC555, NE555, timer

UPDATE: Low-power MOSFET mini-course and battery operating voltage switch-off delay


This electronics mini-course on low-power MOSFETs focuses on a special application, the delay circuit, often called a timer. Nevertheless, this content is suitable for deepening already acquired basics about this type of field effect transistors. For the reader who does not yet know what a field effect transistor (FET) is, the corresponding basic courses by Patrick Schnabel are recommended. These can be found quickly with the ELKO search function through the entries of field effect transistor, MOS circuit family, MOS-FET and MOSFET. This electronics mini-course deals specifically with the BS170, which is very well known and loved. It is often jokingly called the BC109 of the MOSFET families, although it is considerably superior to the BC109.

This mini electronics course begins with a comparison between a Darlington circuit with two NPN transistors and the low-power MOSFET in N-channel technology, with the BS170. This includes a simple principle of how a very simple timer circuit can be implemented. It quickly becomes clear what advantages a MOSFET circuit has over the Darlington circuit. The sideline clearly explains why a Darlington circuit in switch mode (saturated state) has a collector-emitter voltage that cannot be less than a base-emitter voltage.

After that, the focus is fully on the BS170 MOSFET. The transfer characteristic is explained in the context of how it is possible that after a long delay of about 6 minutes, only a switch-off time of about 5 seconds occurs, and this with the simplest analog method. This very detailed explanation is the main subject of this update. Finally, there is a new circuit diagram with an additional lowdropout voltage regulator. Only with such a voltage regulator is it possible to use a 9V block battery until it is completely discharged.

Your ELKO-Thomas

New BJT, Darlington, FET, MOSFET, TIMER, TRANSISTOR, delay

555 timer IC in CMOS. That's why this version has so many advantages!

It is only possible to see the cover picture accompanying the following text on the main page of the ELKO. So that this is also possible in the newsletter, open the following link in the web browser:


This 555 newsletter article is intended to provide ELKO readers with easier access to the modern and contemporary CMOS version of the 555 timer IC. In the ELKO forum I notice again and again that if any questions arise about a circuit problem with a 555, the old NE555 (bipolar circuit technology) is almost always meant. This is simply because the LMC555 and the TLC555 are often not known at all. There are other makes of 555 ICs other than CMOS.

The recently deceased Swiss electronics guru Hans Camenzind invented the NE555 in 1971. At the beginning of the 1980s, the CMOS version was modernized, e.g. the LMC555 from National and the TLC555 from Texas Instruments. The 1980s were generally in the CMOS break-up phase. So you can see that the CMOS version is already a good 30 years old. The advantages are so clear that you can safely do without the bipolar version (NE555).

In the case of an operating voltage of +15 VDC, this is no more an argument than the better driver capability of the NE555: The CMOS version TLC555 is suitable for +15 VDC (worst case +18 VDC). And for the driver capability in the lower 100mA range, you can use a small transistor with very little circuit complexity when using CMOS. The argument of the price difference and the additional consumption of the print space is irrelevant because the CMOS version does not need an aluminum electrolytic capacitor in the operating voltage to block the much lower current transients.

This brings us to the cover picture: The differences between the old bipolar and the modern CMOS version are shown in three columns. In the left column you can see the differences in the operating currents and also the limits of the maximum frequencies of square voltages at the output. At the maximum frequency of 6 MHz, the LMC555 needs just 7 mA and the NE555 needs a full 60 mA at its maximum frequency of just 600 kHz. The current comparison at lower frequencies also has an impact. The middle column illustrates the simplicity of a time-symmetrical square wave generator with the CMOS version compared to the one with the bipolar version. In terms of simplicity, there are other advantages. In the rightmost column, the current transients (current pulses) are compared when the output stage changes its level. In the case of the CMOS version, this current is 14 times lower and this over a period of time that is 10 times smaller. A 140x improvement! This is exactly why an additional aluminum electrolytic capacitor is only required for the operating voltage of the NE555.

I think all of these arguments are convincing enough to decide to use the CMOS versions of the legendary 555 timer IC.

UPDATE: The link below has a small update that consists of a link summary of all electronics mini-courses that have to do with the CMOS version of the 555 timer IC (LMC555 and TLC555). The last link refers to the Timer-555-ELKO book, a collaboration between Patrick Schnabel and me.

I wish you a lot of joy
the ELKO-Thomas


New555, timer

NE555 inventor Hans Camenzind has died

It is only possible to see the cover picture accompanying the following text on the main page of the ELKO. So that this is also possible in the newsletter, open the following link in the web browser (only the picture of the person):


You can find out more about Hans Camenzind's life's work and his death on August 8, 2012 here:

General555, Timer

Now the time has come: The timer book!

As announced last autumn, Thomas Schaerer and I have published a book on the Timer 555, the most popular IC of all time.

This book is a combination of basics, application-oriented circuits and extracts from data sheets. Everything you need to know about the Timer 555 is bundled in a handy and practical ring binder.


  • diverse application possibilities
  • practical tips on the CMOS version
  • and alternative timer and clock circuits
You benefit in three ways:

You save yourself searching for information from dubious sources and tinkering with non-working circuits.

Experiment with circuits that have proven themselves in practice and have been recreated very often enthusiastically by other amateur electronics enthusiasts.

Thanks to the workshop character, you will learn the basics of the timer with fun and a quick sense of achievement.

Take the opportunity now and order the new timer book at the introductory price of 19.90 euros.

GeneralLMC555CN, NE555, Timer, TLC555CP

Power supply or timer book?

It has been a good year since the book “Electronics Workshop: Operational Amplifiers and Instrumentation Amplifiers” by Thomas Schaerer came out.

We would now like to take the next step and bring out another book. And this time too, Thomas Schaerer's excellent mini-courses should serve as the basis for this. This time we would like to explicitly give you the choice of what the content should be. So that the selection is not too difficult for you, we have made a preselection:


What it may be? A power supply book or a timer book?

GeneralBook, Power Supply, Timer21 Comments

Astable multivibrator / astable multivibrator (NE 555)

The astable multivibrator or the astable multivibrator is an automatic circuit that works immediately after the supply voltage is switched on. This circuit generates a continuous square wave signal as a function of the resistors R1 and R2 and the capacitor C1. The astable multivibrator is the most common application of the NE 555 timer. Most of the time, it is about making an LED blink or supplying a clock-dependent digital circuit with a clock signal.

New flip-flop, NE555, clock generator, timer

Update: Monostable multivibrator with the NE555

The name of the monostable multivibrator (with NE555) comes from the fact that this multivibrator emits a pulse only once at the output (A) when a negative pulse (0V) is present at the input (E).

The monostable multivibrator is suitable for extending a short pulse and setting it to a pulse duration. A variable input pulse at the input becomes a defined pulse at the output.

New tilting stage, NE555, timer

Update: Timer NE555

The NE555 is a monolithically integrated timer circuit which, due to its properties, can be used as a clock, oscillator and for time delays. The NE555 is the standard component for all time-dependent applications in practical electronics. It is so universally applicable that it is considered the most important integrated circuit.

It is seldom that circuits can be set up more easily than with an NE555.

The NE555 contains a timer. The NE556 contains two timers in one IC module. The NE 558 even contains 4 timers in one module.

The NE555 is bipolar. The CMOS versions are LMC555CN (National Semiconductor) and TLC555CP (Texas Instruments).

New LMC555CN, NE555, Timer, TLC555CP