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Which components do I need to change? (555 timer)

Discussion in 'Datasheets, Manuals and Component Identification' started by Croboy, Mar 6, 2013.

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  1. Croboy

    Croboy

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    Feb 16, 2013
    http://www.sentex.ca/~mec1995/gadgets/servo3.htm

    So this is a shematic. I need to put flex sensor (about 40kOhms) instead of potentiometer (2k7Ohms). Can I change something in circut to get the same PWM output signal?

    SORRY FOR MY BAD ENGLISH.
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,838
    Jan 21, 2010
    Increase R2 in the same proportion (40/2.7)*68k and reduce the capacitor (2.7/40) * 390 nF

    You may have some trouble if the capacitor gets too small or the resistor too large -- and you'll be verging on both of them I expect.
     
  3. Croboy

    Croboy

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    0
    Feb 16, 2013
    Thanks for a very fast response. I am impressed.
    What about this 2k7Ohms (R1) does he need to be changed to 40kOhms?
    Thanks again.
     
  4. Croboy

    Croboy

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    0
    Feb 16, 2013
    In Electronic Workbench I had make a change.
    So this 390nF capacitor is now 700nF.

    Potenciometer is now resistor (20kOhm)
    and this 68kOhm is now potentiometer (0-40kOhms).

    I get a nice 2mSec PWM signal on 40kOhms. As you can see on this attachemt.
    DOES IT MAKE ANY SENSE? :confused:
     

    Attached Files:

  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,838
    Jan 21, 2010
    No, did you try what I advised?
     
  6. Croboy

    Croboy

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    Feb 16, 2013
    So this is what I get from your advice. On first picture potenciometer is set to 20% and on the second is on 100%.


    Is this okay?


    I am feeling very stupid but need to ask. :eek:
     

    Attached Files:

  7. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,838
    Jan 21, 2010
    I think that looks about right.

    You need to look at the duration of the pulse, but it should change from 1/1000 sec to 2/1000 sec.

    By eye, it looks to be a little long (and that is what I suggested might happen). You may be able to reduce the capacitor a little more.

    I presume this is simulation? It may not behave quite as well in real life.
     
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