555 high frequency oscillator..help

Discussion in 'General Electronics Chat' started by hertz.12, Jul 27, 2015.

  1. hertz.12

    Thread Starter Member

    Apr 25, 2015
    36
    0
    hi all
    i need to generate high frequency..32khz with ne555 ....my SCHEMATIC DIAGRAM :

    New Bitmap Image.jpg


    but the problem is the output frequency not stable at all.

    when i measure the output frequency it plays around 29800hz..28054hz..30125hz..35458hz !!!! where is the problem??

    i am using pic based frequency counter ..and it work fine and when i am using it to measure 30000hz signal coming from another pic it reads 29756 Hz..it is good for me ..but with 555
    it plays around 29800hz..28054hz..30125hz..35458hz !!!! where is the problem??
     
  2. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,539
    1,251
    First, the output waveform is not a symmetrical square wave, so that might affect the reading. Second, the timing network impedance is very high, making is subject to noise and error currents coming from the 555. The part number in your drawing is for the bipolar device, which contributes much less error to lower impedances. Consider changing the device to the CMOS LMC555. Also, try reducing the two timing resisors by a factor of 10 or 50 or even 100, and increasing the timing capacitor by the same ratio.

    ak
     
  3. ScottWang

    Moderator

    Aug 23, 2012
    4,855
    767
    1. Are you tried the circuit on the breadboard?
    2. Using the wires as short as you can, and the better way is soldering the components on Universal PC board.
    3. Change the values of R1,R2 and C1 as R1 = 1K, R2 =22K, C1=0.001uF(102)

    Online 555 Astable Circuit Calculator.
     
  4. hertz.12

    Thread Starter Member

    Apr 25, 2015
    36
    0
    thanks all guys ..i will try soldering the components on Universal PC board and reduce the values of r1 r2 c1

    i hope that will solve the mess
     
  5. AnalogKid

    Distinguished Member

    Aug 1, 2013
    4,539
    1,251
    Reduce the resistors. *Increase* the capacitor.

    ak
     
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