MATH/S FREQUENCY help!

Discussion in 'The Projects Forum' started by tibbles, Jul 22, 2014.

  1. tibbles

    Thread Starter Active Member

    Jun 27, 2008
    249
    3
    hi
    im hoping to build this http://www.slottechforum.com/slotin...ltage Comparators/LM339/LM339 oscillators.pdf bottom left
    unfortunately ive met my nemesis- math/s.

    r12 and c1 what units to use?
    1/f intermediate frequency or more likely 1/f ?
    >> much more than?


    if i assume say r12 =25k=25000 ohms
    " " c1 = 1n =.000001 farads
    = .025
    1/.025 =40 hz - when i should be looking for a few thousand hz on these figures, according to a similar example.

    the xtal is 2 MHZ, i'm using a high speed comparator.

    hope someone can help

    doug
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,979
    744
    R is in Ohms, C is in Farads, 1uF is 0.000001, 1nF is 0.000000001, 1pF is 0.000000000001. , work backwards so 1/F = RxC

    So your values R 25k x 1nF=0.00025Sec =40Khz

    2Mhz is a 10K resistor and 50pF cap.
     
    Last edited: Jul 22, 2014
  3. tibbles

    Thread Starter Active Member

    Jun 27, 2008
    249
    3
    thanks DODGYDAVE youve saved my life,i'm glad you did it with zeros rather than powers of ten, which i never could get my head round,after all its easy to cancel most of the zeros.
    thanks again,
    doug
     
    Dodgydave likes this.
  4. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    the powers of ten tell you how many zeros to cancel or add. 10 to the 6th, 1 with 6 zeros. one millionth, 1 times 10 to the -6, put the 1 in the sixth place to the right of the decimal point.
     
  5. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    2,802
    832
    Errr...

    1 times 10 to the -6 (minus 6), you would put the 1 in the 6th place to the right of the decimal point.
     
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