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help me about 555

Discussion in 'Electronic Basics' started by E.persia, Sep 4, 2008.

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  1. E.persia

    E.persia Guest

    I have a project that is connected with the famous 555 timer
    I want ask you if you know a newwer chip with the better feature ...
    this is very urgent to me
    thank you all!
  2. ian field

    ian field Guest

    There's also an ultra low voltage type - The ZSCT555 from Zetex which works
    down to 0.9V.
  3. Yukio YANO

    Yukio YANO Guest

    I came across a 555 chip with an on board programmable divider ! This
    increased the range and accuracy !

    Part of a Timer I disassembled about 25 years ago don't remember the
    Chip # ?

    Yukio YANO
  4. Bill

    Bill Guest

    A divider would increase the range and resolution, but not the
    accuracy, which is determined by the oscillator (R, C, threshold
    variance, etc). If the oscillator is 5 % accurate to generate a 50 ms
    pulse, it is also 5 % accurate to generate a 5 minute pulse.

  5. Rich Grise

    Rich Grise Guest

    His homework.

  6. The XR-2240. Put a ripple counter in the same package as an RC timer.

    But, the thing about the 555 was that it was general enough to find
    lots of use. You could use it as a monostable, or an astable, you could
    use it as a latch, you could use it as a driver when more current was
    needed, you could use it for all kinds of things. Because while it
    was designed as a timer, it brought enough out to the pins to make
    it versatile. It came out at a time when CMOS was barely available,
    and TTL was king, yet here was a device that could do some logic functions
    yet run over a wider voltage range than TTL.

    It was succesful, because of that versatility. The early datasheet
    and application note were full of things you could use it for that
    wasn't about "timing". And as soon as it was out of the gate, other
    people cooked up things to use it for.

    The success brought other IC timers. Walter Jung's IC Timer Cookbook
    from about 1977 is full of various things you could do, and the also
    rans that came along in the wake of the 555. Quad timers like the 558.
    Things like the XR-2240. "Precision timers", the numbers I can't

    Yet those also rans are vague to most, because they never
    had the success of the 555. They undoubtedly were good for what
    they did, but they didn't do much beyond what they were good for.
    It was much easier to stock the 555, and add a counter or whatever,
    than to have all those different types of IC timers around, which
    much of the time wouldn't have a use.

  7. But, if you've got a really long time period, it's far easier to
    adjust a clock running much faster than waiting all that time to
    see if the output matches the desired time. You can adjust and
    see the results almost immediately, whereas if you've got a 555
    with a 5 minute cycle, you have to wait five minutes between
    any adjustment.

    Plus, it's easier to get better tolerance capacitors in small
    values than cheap electrolytics, which is what a lot of people
    would end up using if they needed long time periods. Likewise
    the resistors become reasonably valued, rather than tens of megohms
    where external factors may add resistance in parallel to the
    timing resistor.

    It's not that the XR-2240 makes things more accurate, but the
    arrangement makes it easier. Of course, you can do the same
    thing with a 555 and a separate divider.

  8. E.persia

    E.persia Guest

    hi every body
    I think you are right
    may be my explaination make the subject more obvious
    I'm gonna make a moisture capacitive sensor for a specific oilseed ...
    the moisture will be checked by the capacity that will change respect
    to the dielectric beetween the plates(the oil seed)
    I use this capacitive as the C in unstable multivibrator to make
    square waves with diffrent T that a micro going to read it and so on
    but my problem is :because of the C range (50 to 100 pf) I have to use
    very big R to have a better T and in that way it can't feed the
    current for 555 to be in the ideal range of work
    so it's my complete problem
    is ther any ic for me
    is there any way to sove this problem

    thank you all!
  9. gs

    gs Guest

    Well there came a nice LM3905 with some neat features, then
    they got rid of it.

  10. Jamie

    Jamie Guest

    Use a dual 555 (556) system and gate the outputs as mixer effect.
    you set one at a standard with a null pot and the other will
    be attached to the capacitor plates.

    With that, you can select a much higher range of frequency to
    work with and product a lower freq offset. etc.."
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