17

I've noticed is that 555 ICs seem to be extremely common. Why is the 555 so prevalent, or ubiquitous; what about it so useful?

Community
  • 1
voices
  • 1,039
  • 1
  • 15
  • 29
  • 1
    I fail to see how this question is relevant to electrical engineering. What problem are you trying to solve? – Bart Aug 23 '17 at 14:33
  • 1
    @Bart: it's probably fair enough question if we go into the inner details. – Transistor Aug 23 '17 at 14:36
  • 1
    The 555 has internal circuits (constant currents) to charge up to 2/3 of VDD and then charge down to 1/3 of VDD. The near-50% duty cycle output, with high drive current, makes the 555 popular. – analogsystemsrf Aug 23 '17 at 14:37
  • 9
    I think your premise is wrong. The 555 might be common in sketchy designs you find on the internet, but I would not definitely define it common in the professional sphere. – Vladimir Cravero Aug 23 '17 at 14:42
  • 22
    @Bart You're not trying very hard if you can't see any relevance between a question about the 555 and electronics. While it's important to be vigilant about off-topic questions, there is such a thing as over-policing. – jalalipop Aug 23 '17 at 14:45
  • 1
    To reinforce "cheap and popular": among the 23,293 chips in Digikey's timing category, nearly all of the least-expensive and most-stocked devices are 555 or 555-derivatives, with hundreds of thousands of devices in stock. – Reinderien Aug 23 '17 at 14:54
  • A bit off on a tangent, but Ben Eater's 8-bit computer building series has three videos going in-depth about the 555 timer. The first one is [here](https://www.youtube.com/watch?v=kRlSFm519Bo), and the first 15 minutes of that details the inner workings of the chip, and the rest of the videos tells you how to use it. Without knowing how familiar you are with them, if you want to understand it better, I would say that that's a good place to start. – Arthur Aug 23 '17 at 16:21
  • 9
    I see you've asked 14 questions but only formally accepted one answer. I can see several questions you have raised that have good answers so is it just laziness that prevents formal acceptance of answers? Call the formal acceptance of an answer a fee for getting good information and you should therefore consider revisiting earlier questions. – Andy aka Aug 23 '17 at 16:35
  • 1
    @VladimirCravero it is certainly a rare find in junk PCBs compared to LM324 and derivative opamps - THESE are really everywhere... – rackandboneman Aug 23 '17 at 18:37
  • 1
    @Andyaka if I'm satisfied with an answer and it helps me, I'll accept it. Unfortunately, I mostly seem to encounter pompous attitudes, opinions, and ad hominem criticisms such as yours; unrelated to the knowledge, or information that I'm looking for. – voices Aug 24 '17 at 01:35
  • 1
    The 555 timer is popular because people are superstitious and don't want to use the [666 timer](https://xkcd.com/730/). – reirab Aug 24 '17 at 03:00

4 Answers4

40

I'm not a 555 fan and only used them a couple of times over several decades but they do have their uses.

Why is the 555 so prevalent, or ubiquitous; what about it so useful?

  1. It was probably the first general purpose timer to market. (Timing is everything!) It was featured in all the hobby electronics magazines of the 1970s, etc., so it became very well known.
  2. "555" was easy to remember. (Don't laugh!)
  3. It has a wide working voltage range - 4.5 to 16 V. This beat any of the logic families.
  4. It was flexible. Oscillators, monostables, pulse generation, sequential timing, time delay generation, pulse width modulation, pulse position modulation, linear ramp generator, etc., could be formed with only a few components.
  5. Due to the 1/3 and 2/3 Vcc switching points the timing was pretty much independent of voltage. This is useful for battery powered circuits in particular.
  6. (Only?) 50 ppm temperature drift.
  7. 200 mA output source or sink capability. Again, this beats any of the standard logic families and allowed direct drive of LEDs buzzers, speakers, motors, etc.

enter image description here

Figure 1. Internals of the 555. Note that all transistors are BJTs.

  1. It was tough. The device is built using regular transistors (see Figure 1) which are fairly tolerant to electro-static discharge (but see 11.2 on datasheet below).
  2. Price is very low.
  3. For all of the above reasons it made a great chip for "my first project" tasks. A capacitor, a few resistors and an LED were all that was required to get someone started on the road to becoming a major EE.SE contributor.

Ref: TI 555.

Transistor
  • 168,990
  • 12
  • 186
  • 385
  • 9
    +1 for #9 esp .. You have to wonder just how many EEs got their baptism with 555s and the ubiquitous 741.. (I know... blasphemy LOL) – Trevor_G Aug 23 '17 at 14:54
  • R7,8,9 set the 2/3 and 1/3 thresholds. – analogsystemsrf Aug 23 '17 at 17:57
  • 1
    CD4060 (CMOS) has a wide voltage range too. – Jasen Слава Україні Aug 23 '17 at 20:03
  • 1
    @Jasen: I spotted that as I re-read it after I wrote it. I don't know what part of my head it came from. CMOS is better in that regard at 3 V to 18 V if my memory is correct. – Transistor Aug 23 '17 at 20:08
  • Re #8 Still true? I remember an electronics hobbyist complaining to me sometime mid-200Xs that it was now cheaper for them to use a microcontroller to do some timer job than it was to use a 555. Price of one-off discrete bits for hobbyists may not bear much relation to industry bulk pricing of course. – timday Aug 23 '17 at 22:06
  • The chip itself is still dirt cheap but the passives needed can make the overall solution cost more an a micro (especially for long delays). OTOH a 555 doesn't need to be programmed. – Peter Green Aug 24 '17 at 00:30
  • 1
    as a side note 5 in Thai language is "ha" so people often write 5555555 when laughing. 555 would be "hahaha" so it's not only easy to remember but also fun to say – phuclv Aug 24 '17 at 01:22
  • 2
    @timday - [You can buy 555s for less than 3p each](https://www.aliexpress.com/item/50PCS-NE555-555-DIP-8-IC-Timers-NEW-GOOD-QUALITY/32663603008.html), which is somewhat cheaper than any microcontroller I've ever seen. – Jules Aug 24 '17 at 04:01
  • @Julies. That's based on a bulk price for 50 though. I think the person I spoke to had been to Maplin to get a single one; they're currently listing 29p for a single, but if I check the wayback machine for the same page it'd have been 99p in early 2014 (furthest back it has for the page). I seem to remember they were comparing with some low-end PIC processor and it's not impossible those could have been sub £1. Probably all just a quirk of Maplin retail pricing... certainly RS Components have 555s for 20p/10p/7p if you buy them in ~10/25/2500 quantities. – timday Aug 24 '17 at 10:49
17

The IC was designed in 1971 by Hans R. Camenzind under contract to Signetics and introduced in 1972. The 555 is still in widespread use due to its low price, ease of use, and stability. It is now made by many companies in the original bipolar and in low-power CMOS. As of 2003, it was estimated that 1 billion units were manufactured every year. The 555 is the most popular integrated circuit ever manufactured. Wikipedia

As you can see the 555 is a really old design that has simply stood the test of time because, for a quick and simple method to perform various functions at lower frequencies and tolerances, it is simply really hard to beat at the cost. That being said, many serious designers may say that using them is "cheating".

There are many, many circuits designed around it out there, many of them quite interesting in how people have found novel ways to use them. There are even books dedicated to the old lady.

The points @Transistor raises in his answer also sum it up... a classic example of...

"When you get it right the first time it will stand the test of time".

Daniel
  • 1,600
  • 3
  • 16
  • 24
Trevor_G
  • 46,364
  • 8
  • 68
  • 151
  • 1
    "Old lady"? Oh, dear...I've been guilty of elderly abuse. But now its child abuse: mostly microcontrollers instead of old-lady-555. – glen_geek Aug 23 '17 at 15:38
  • 2
    From a less hobbyist point-of-view, I can highly recommend the book Hans Camenzind (RIP) wrote: **Designing Analog Chips** . He made it available in pdf form, and you can find it [here](http://www.designinganalogchips.com/_count/designinganalogchips.pdf). Some 555 history is contained within, as well as improvements more than a generation later. The print edition is not particularly expensive. – Spehro Pefhany Aug 23 '17 at 19:11
9

It depends on what you mean by common.

The 555 is very widely used on hobby and home brew projects and in simple example circuits as found on the web. This is because it's flexible, simple to use and works off a huge voltage range making it ideal for use in quick and dirty simple circuits where high precision isn't required. It's also old enough that there are lots of examples around of how to use it since it features in some of the earliest books and tutorials.

It's not common in modern professional designs where it is considered too inaccurate for most applications and the required functionality can normally be implemented elsewhere without requiring an additional component.

The other part you will see a lot is the 741 op-amp. It's a dinosaur, modern parts out perform it in every possible way but people still want to use it.

Andrew
  • 6,872
  • 19
  • 25
2

The 555 was an early champion. I used a lot of them from around 1971 to 1976, as well as some multi-555 chips. I eventually became dissatisfied with such timer/oscillator parts because they could put a lot of noise onto the power and ground buses when charging and discharging the user-supplied timing capacitor.

Later all these single-function parts became largely irrelevant. As time went on, most simple operations were being performed by code on microcontrollers which had their own carefully designed clocking arrangements, analog and digital io lines, etc., etc.

Those early years of designing with op amps, 555 chips and 7400 digital logic were fun, exciting times. In retrospect that period was just a phase. For better or worse, the world of electronics is completely different now, with the nuts and bolts of electrical engineering not so easily accessible to the student and hobbyist.

Ralph Dratman
  • 121
  • 2