timers other than 555

Discussion in 'General Electronics Chat' started by shortbus, Jul 6, 2015.

  1. shortbus

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    Not wanting to hijack a thread, http://forum.allaboutcircuits.com/threads/time-delayed-switch-trigger-by-opening.113144/ it was perfect for a question I have. Why doesn't anyone use any of the other timers, other than a 555? It seems to be the only one people use.

    The cd4538, cd4098, and many others seem to do things that the 555 can't. The main one being able to use either a rising or falling edge as a trigger. They can be used as an astable or monostable and have many of the same traits as the 555.

    Another of my 'million dumb questions'.
     
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  2. dl324

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    Appearances can be deceiving... It's often a matter of preference, what you have on hand, board space, etc. I bought a few tubes of 555 timers in the 70's and still have dozens of them. I also bought CD4538 by the tubes. When I designed a SLA battery charger, I used CD4538.

    You could make the same statement about voltage regulators; many on this forum seem to use LM317. Same for opamps, transistors, ...
     
    Last edited: Jul 6, 2015
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  3. AnalogKid

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    I agree that if you need two monostables and a low power output, either chip is more configurable than a 555. But the 555 has two astable modes, that fat output stage, and as a single is seen as a better fit to most applications. This is supported by the fact that the 555 outsells the 556 by about 10:1.

    ak
     
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  4. JohnInTX

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    How about TimerBlox from Linear Technology? Pretty simple. Cheap too.
     
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  5. OBW0549

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    Familiarity, versatility and timing accuracy are probably the three most common reasons.

    I rarely use even 555's anymore, or the dual timers (556); I just use one of the low-end PICs like the PIC10F322, PIC12F675 or the PIC12F683. They're even more versatile, they're easy to program, and they're cheaper than dirt.
     
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  6. MikeML

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    I find that I can do a lot of timing functions with an RC network on the gate of a power MosFet, which can source or sink Amps. The 555 can source or sink ~200mA, while CMOS timers are lucky to source or sink 20mA. By the time you add the MosFet (or Darlington) to a timer chip to switch a load, you might as well do the timing on the gate of the MosFet directly...
     
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  7. crutschow

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    As I'm sure you're aware, the main disadvantage of using only the MOSFET is timing accuracy. The large variation of Vgs(th) and it's variation with temperature means the timing period can exhibit significant variation in the timing period between units and, to a smaller extent, over temperature.
    If that's not a problem in the application, then the MOSFET is certainly a simple solution for simple one-shot timing requirements, particularly those requiring higher currents.
     
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  8. MikeML

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    Most of my applications are one-of, so trimming to get the time I want is no worse than finding a +-5% or +-1% timing capacitor...;)
     
  9. JohnInTX

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    +1. For the time and effort it takes to do a 555 with all its quirks plus implementing whatever logic that you are timing, I'd think you could take that time and come up to speed on PIC for simple logic/timing stuff.

    The 12F1840 is a little 8 pin jewel. It's enhanced midrange (no goofy r-m-w issues) and incorporates a SR flip/flop, comparator with precision reference, DAC and more. The f/f can be configured to drive an output and in addition to firmware control, can be set up to direct trigger on a pin input, the comparator etc. for no firmware overhead if desired.
     
    Last edited: Jul 6, 2015
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  10. WBahn

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    If the only tool you own is a hammer, every problem looks suspiciously like a nail.

    Many people only learn about the 741 opamp, the 311 comparator, the 317 voltage regulator, and the 555 timer. That's because (and I'm doing a bit of speculating here) the textbooks they learned from only used these. Why? More speculation -- the people that write textbooks usually come from an almost exclusively academic career and many have never actually built a circuit other than what is done in an undergraduate lab course. So they use what they are familiar with and for the kinds of circuits that are in most texts, it doesn't really matter.

    So students that become engineers do what most humans do -- they use what they know how to use until that just doesn't cut it any longer.

    I really don't have much of a problem with introductory courses sticking to a simple and limited components selection such as this as students are first coming up to speed on the concepts and getting a taste of non-ideal behavior. But what is really need in the curriculum is a senior level course on real-world engineering where the students work on projects that simply will not work unless the students learn to do a moderately good job of component selection. It would be frustrating, but they would learn a hell of a lot and, I think, many of them would find it super enjoyable.
     
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  11. AnalogKid

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    "I suppose it is tempting, if the only tool you have is a hammer, to treat everything as if it were a nail."
    Abraham Maslow, The Psychology of Science: A Reconnaissance, 1966

    Hence my tagline.

    ak
     
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  12. WBahn

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    I wonder if that was original, or if it dates back further. My guess is that it does, but you never know.

    It's one of my favorite sayings, because it is SO true!
     
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  13. #12

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    As a person who paid my mortgage repairing things, I object to replacing everything you can with a programmed microprocessor because I can't buy one and solder it in without going to the manufacturer, who won't sell me one. On the other hand, that is what the world is coming to and I am a dinosaur.

    Rather consider what this site would be if the first answer for most requests was a microprocessor. I think there is enough fodder for conversation in that sentence to merit a thread of its own.
     
  14. JohnInTX

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    Good point. I paid my mortgage designing microcontroller things and now, in semi-retirement, kind of get my kicks out of repairing my various appliances, pool stuff, neighbor's pool stuff etc. at the component level - and have to stop at the micro. I have a hammer-nail thing going with PICs, I guess. But I have also done lots of 555, know their quirks, and when I discovered 4K+ of them on a skid that I bought at auction way back, gave them away to an unemployed buddy to sell on Ebay.

    I do understand the frustration, I really do. And I also feel somewhat jurassic these days - while I can pack 8.7lbs of spec into a 5lb micro, it's pretty moot when for the same price you can buy a 100lb micro and get someone to throw C at it until something sticks.

    Noted. But that's where things kind of are these days, yes? For the price of one decent cap for the 555, you could buy several 12F micros. I guess the answer depends on how you want to do the job. Myself, I'm more tooled towards the micro approach. I respect other approaches as well. Just.. 555?

    Prescient to the last!

    Props.
     
  15. AnalogKid

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    Actually, I do, and no, it doesn't. Back in my university research instrumentation days I worked with a Psychology department. Among the faculty were one of Maslow's former students and a former student's student. They had the full story of how he came up with the phrase. Unlike Freud's line about eyes and windows, this one was an original.

    ak
     
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  16. ronv

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    I think the main advantage of the 555, 556 is that they can drive a lot of current. This makes them handy for more things like drivers, leds and optos that the CD parts just can't do.
     
  17. GopherT

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    @shortbus
    The 4538 can achieve one-shot pulse of 1 uSec whereas the 555 Lower limit is 10 uSec.

    Also, idle current of 4538 is a few NANOAmps and NE555 is a few mA with no load.
     
  18. shortbus

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    Thank you all for answering! I was pretty sure the most common answer was the output current. but if your just using with other logic chips, it didn't make sense to me to use a 555. Especially if you need some precision. It's hard for me but I am learning a lot from all you guy's here. Thank you all!
     
  19. atferrari

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    It seems to be the only one people asks questions about, I think. And, as suggested in the CD4000 family there are interesting alternatives.

    Ah, yes, the beefy output stage, an advantage.
     
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  20. ronv

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    The initial timing specs on the 555 are quite a bit better as well as it's performance over temperature and supply voltage. Probably only a problem if you want to make something without an adjustment.
     
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