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Using Stamp to control the frequency of an astable 555 timer — Parallax Forums

Using Stamp to control the frequency of an astable 555 timer

Turnbull2112Turnbull2112 Posts: 65
edited 2008-08-26 03:12 in BASIC Stamp
I am trying to make a half bridge driver from three 555 timers and the frequency is controlled by the stamp. I am trying to use the 128 pos digital pot to vary the resistance of the RC circuit however the turndown is choppy as the pot "steps." Does anyone have any ideas about how to do this where I can get a smooth turndown over the frequency range? I am pretty green to this stuff but I am trying my best to learn. Thanks.

Comments

  • PJAllenPJAllen Banned Posts: 5,065
    edited 2008-08-24 18:57
    128 positions isn't a lot of resolution.· I would choose a capacitor and probably a series resistor to make the most of it, "tuning" as narrow a range as possible.
  • Turnbull2112Turnbull2112 Posts: 65
    edited 2008-08-25 01:08
    My range is 1khz.
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2008-08-25 01:29
    1kHz wide
    What is the low freq, the high freq, and what's the value of the 128-step pot (can your provide a link to the 128-step pot's datasheet )?
  • Turnbull2112Turnbull2112 Posts: 65
    edited 2008-08-26 00:08
    The low will be around 2hz and the high will be around 1khz. There used to be a chip called an NE566CN voltage controlled oscillator(obsolete) and I cant find a crossover. Varying the voltage signal would vary the frequency. There has to be some way to do this with the stamp and a digital to analog converter·or something similar.·I dont think Im going to waste any more time on the digital pot.
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2008-08-26 00:12
    OK.· We won't pursue that angle any further.

    You may appreciate knowing that the VCO section of the 4046 (CD4046, 74HC4046) is the same thing, works the same way.· It's still very available (Jameco, Mouser, &c.)
  • Turnbull2112Turnbull2112 Posts: 65
    edited 2008-08-26 00:34
    Well hell yea!! Thanks for the heads up! Ill probably use a transistor with a DAC to throttle the frequency on that guy.
  • Dave-WDave-W Posts: 94
    edited 2008-08-26 03:12
    How about using a LM331. 1hz to 10KHZ with feq components and can be configured to your needs.

    See attached.

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    Dave W.
    pdf
    pdf
    00568005.pdf
    13K
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