The ever present 555 timer - Page 1
Forum section: electronics / beginners

author: wa2pux
author_rank: Contributor
timestamp: December 16, 2021, 08:14:47 pm
content: I had aLOTof fundiving into the 555 timer which was first released to the public in 1972 as the NE555.It was an instant success and remains a favorite of electronics experimenters world wide. You can even buy them on Amazon!It has survived for almost 50 years and has been recreated by many manufacturers in many shapes. At one point the dual 555 timer (the 556) was introduced to the market. I think there is even a quad version available somewhere!So, my dive into exactly how this thing works lead me to understand some of its foibles, as well.I spent over a week putting all of this together in my video on the topic available here for your edification:https://youtu.be/04IsNMdhzK0

author: MK14
author_rank: Super Contributor
timestamp: December 16, 2021, 09:34:31 pm
content: I've watched your video, and enjoyed it, thanks!Tiny, tiny, correction (I'm impressed with your technical accuracy overall).At just after 1 min 20 seconds in, you said the ninth pin, would have forced it into a 16 pin package.I presume you meant 14 pins.I'm taking three assumptions.(1) 14 pin DIPs were available then(2) Signetics had 14 pin packaging machinery, they may have been limited to 16 pins(3) You weren't assuming 2 555 timers would have been in the same package, sharing power pins to fit it all in, as a compromise to not having an 8 pin variantYou have sparked my interest, so reading more (wiki article) about the 555 chip. It was named 555 timer, by the sales manager, not because of the 3 x 5K resistors.

author: Stray Electron
author_rank: Super Contributor
timestamp: December 17, 2021, 12:55:05 am
content: One of my jobs in a past life was to maintain and repair a very large food packaging machine for McCormick Corporation (the people that make and sell all of the spices). There were no CPUs or digital electronics in it. Instead it had a couple of dozen 555 timers that controlled every function and each timer triggered the next one and so on and so forth. All timing was analog and every circuit on every board had to be individually adjusted. Downtime on that machine costs the company $60,000 per hour. And that was in about 1980! I was paid to sit next to that machine night and day and to make sure that it always ran exactly as intended. People laughed because I always carried a Bourns pot tweaker in my shirt pocket but I still have it.Spare boards cost $20,000 each so we only had a few. But I designed and built test fixtures for the boards so that we could test and repair them in-house. And any time that the production line was down for other reasons, I would shove a spare board into the machine and test it and make all of the adjustments. Then I'd pull the board and save it as a ready spare. It got to the point that if a board failed I could swap in a new board and have the machine running again within a minute. That made the company VERY happy. Previously, they had been buying spares but not pre-adjusting them so replacement and realignment took them hours. They had also been returning the failed boards to the manufacturer and had been paying a flat rate of $5,000 per repair. I was the first electronics tech that they had ever hired but they told me that I saved them hundreds of thousands of dollars the first year. One machine that I build for them cost about $8,000 and took about 3 months to build in-house but they had been quoted $200,000 and 8 months to build by an outside company.Fun fun!Tip, the reset signal operated differently on the Signetics 555 than everyone else's 555s. I don't remember which is which but in one the Reset overrides the Trigger signal and in the other, the Trigger overrides the Reset. Somewhere I think I still have a bunch of Signetics 555s that I acquired in about 1976 or 1977.I also still have my copy of the 555 BugBook, published by H W Sams Company. I doubt that I will ever part with it. Even though I'll probably never read it again.IIRC... Later there was a Quad version of the 555 called a 558. There was also a dual 555 called a 556. There was also a 7555 IC. It was a 555 with a built in programmable digital divider circuit. With it you could get delays and/or output period that were DAYS long.

author: Infrared_Fred
author_rank: Regular Contributor
timestamp: December 17, 2021, 02:06:34 am
content: Quote from: Stray Electron on December 17, 2021, 12:55:05 amJYSK that at least now seems to be a CMOS 555, based on what digikey has it is just listed as being a CMOS version of the 555, so you can do longer delays due to much higher input impedence, but there is no digital divider built in. do you know of a datasheet for the ones with the digtal dividers by any chance? They sound interesting to check out. Thanks!

author: latchesheyhey
author_rank: Newbie
timestamp: December 17, 2021, 03:01:38 am
content: Very detailed sharing! Thanks!

author: Stray Electron
author_rank: Super Contributor
timestamp: December 17, 2021, 03:34:19 am
content: Quote from: Infrared_Fred on December 17, 2021, 02:06:34 amHmmm. <https://www.nxp.com/docs/en/data-sheet/ICM7555.pdf> It appears that you are correct and the 7555 doesn't have divider stages but I'm sure that I read of a version of the 555 that did. The 7555 is an 8 pin device and the one that I remember was 14 or maybe 16 pin. I never worked with the (7555)?, I only read about them. From what I recall the timer section isn't very different from a normal 555 but I think that it did have a slightly wider frequency range. The big difference was that the package included several stages of dividers, each stage with an output pin so you could divide the 555 stage output by something like 1,000. Yes, the (7555)? was CMOS and drew much less power than the earlier 555s but I don't know if that affected the operation and specifications. I think that today, all 555s, 556s, etc are all made with CMOS.I'm looking around and I see that they also now make a dual version of the 7555, a 7556 <https://www.renesas.com/us/en/products/clocks-timing/application-specific-clocks/general-purpose-timers/icm7556-general-purpose-timers>I might be dis-remembering the 4060 IC <https://www.homemade-circuits.com/how-to-understand-ic-4060-pin-outs/> and <https://microcontrollerslab.com/wp-content/uploads/2020/01/CD4060-Datasheet.pdf> and <https://microcontrollerslab.com/cd4060-counter-pinout-working-examples-datasheet-applications/>

author: Ian.M
author_rank: Super Contributor
timestamp: December 17, 2021, 05:33:50 am
content: Perhaps you are thinking of an Exar XR-2240. Compatible parts were also manufactured by Texas Instruments (as the uA2240C) and National Semiconductor (LM2240).http://patrick.hiebel.free.fr/doc_semiconducteurs/lineaires/ua2240.pdfAlso see:https://www.eevblog.com/forum/projects/ltspice-simulation-madness-xr-2240ua2240lm2240-programmable-counter-timer/

author: gbaddeley
author_rank: Regular Contributor
timestamp: December 17, 2021, 08:30:57 am
content: Memories. My first ever electronics money making venture was a photographic enlarger exposure timer using the 555. I designed made and sold about 10 units in ca. 1977. It had push-on-push-off buttons to adjust a mains relay closure from 0.5 to 60 secs. I was 16. It was great fun.

author: Stray Electron
author_rank: Super Contributor
timestamp: December 17, 2021, 04:12:35 pm
content: Quote from: Ian.M on December 17, 2021, 05:33:50 amYes. I think you are correct. That looks more like what I remember and I think that the circuit I remember did have a built in voltage regulator. All in all, it looks like an incredibly useful part.To quote from the data sheet: "Using two circuits in cascade can provide precise time delays of up to three years". That was what REALLY stuck in my mind at the time.Thanks for taking the time to find this and post it.