Pulse width modulator with lm555

Discussion in 'The Projects Forum' started by Mariel, Mar 2, 2008.

  1. Mariel

    Thread Starter New Member

    Mar 2, 2008
    3
    0
    Hi everybody!

    I'm from argentina and i'm trying to do a Pulse width modulator with lm555 but i'm having errors in the design. I really need help on this. I'm using the lm555, a resistance and a capacitance thats all but when i tried to put the value of them (i need 20kHz cos this is an audio signal) i couldnt modulate the signal.

    I really apreciate all the information you're able to provide me!

    Thanks in advance!!

    Mariel:p
     
  2. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
  3. HarveyH42

    Active Member

    Jul 22, 2007
    425
    5
    Post your circuit, more likely to get specific help. Shouldn't be that complicated. I built 555 servo tester a few months ago. Remember there being a diode or two in there. Using a microcontroller now, that one has been scrapped.
     
  4. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    See the attached circuit. Your minimum duty cycle will be around 4.6% due to R1 being 1k. However, at minimum duty cycle, R1 will have 12mA flowing through it if Vcc=12v; you really wouldn't want to reduce R1 below what it is already. However, the frequency of the circuit should be right around 20kHz, mostly depending upon how accurate C1 is. Use a tantalum, poly or ceramic cap.

    For D1 and D2, use 1N4148 or 1N914. 1N400x would probably be too slow.
     
  5. Mariel

    Thread Starter New Member

    Mar 2, 2008
    3
    0
    Hi all!!:p
    I have to modulate an audio signal and then I have to demodulate it. I'm working in the modulation part. i put a pulse signal in the trigger pin and the audio signal in the control pin and then I put the frecuency with the resistence and capacitance using the 555 in monoestable status but using t(high)=1.1*R*C but i couln't modulate the right signal. Is this correct?:confused:

    Thanks in advance!!!
     
  6. S_lannan

    Active Member

    Jun 20, 2007
    247
    2
    if you want to pulse width modulate an audio signal have a good look at this article

    http://sound.westhost.com/articles/pwm.htm

    it explains how a signal is pwm'd and turned back into a normal audio signal.
     
  7. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    How about posting the circuitry diagram of what you have designed so far so that we can take a look and comment on what you might do to improve it.

    hgmjr
     
  8. peranders

    Well-Known Member

    May 21, 2007
    87
    0
    Have you checked the National website?
    http://cache.national.com/ds/LM/LM555.pdf figure 8
     
  9. Mariel

    Thread Starter New Member

    Mar 2, 2008
    3
    0
    Yes I used that circuit in monostable operation.

    Thanks!!
     
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