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Wave Form Graphs Question — Parallax Forums

Wave Form Graphs Question

Martin_HMartin_H Posts: 4,051
edited 2011-02-23 07:56 in General Discussion
I am reading the propeller tutorials on the gadget gangster web site and noticed something that confused me. Here's the tutorial link:

http://www.gadgetgangster.com/tutorials/373

The wave form graphs don't have their axis labeled. I had assumed they were amplitude versus time, but Nick replied that they were frequency versus time. This confused me as I would think that a frequency versus amplitude for a wave form would look like a set of harmonics tailing off in amplitude.

So anyone care to venture what the axis are on the square, triangle, and sine wave form graphs?

Also, I maintain a web site and know that answering questions is a catch as catch can enterprise. So I understand that Nick is likely busy and likely missed my question. I'm just glad he has these tutorials up at all!

Comments

  • Heater.Heater. Posts: 21,230
    edited 2011-02-22 11:25
    Looks like amplitude vs time to me.
  • UnsoundcodeUnsoundcode Posts: 1,532
    edited 2011-02-22 13:00
    Hi Martin , the X axis is time , by which frequency can be measured , and the Y axis is voltage which being the Propeller output would swing between 3.3 and 0v. Tone is altered by increasing or decreasing frequency , the graphs shown seem to have approximately the same frequency if the X axis are the same time base.

    Jeff T.
  • Martin_HMartin_H Posts: 4,051
    edited 2011-02-22 16:43
    Good, thanks to both of you. Which means I understood them, but that mean my original question to Nick remains.

    A propeller chip's pin is either 0 or 3.3 volts, so how would it produce any wave form other than a square wave?

    Sorry if this is a basic question, but signal processing is a big weak spot of mine.
  • UnsoundcodeUnsoundcode Posts: 1,532
    edited 2011-02-22 16:58
    Hi Martin , a digital signal can be modified using capacitors , inductors and resistors .

    I can't tell you exactly how that is the limit of my knowledge on wave forms.

    Jeff T.
  • Heater.Heater. Posts: 21,230
    edited 2011-02-22 21:57
    Yes, the digital output can only be 0 or 3.3v.
    BUT you can arrange that the proportion of time that it is high is say 30% and low is 70%, then the average output voltage is 1.1volts. The average can be got by filtering with a capacitor and resistor. Change the high/low time ratio and you changr the resulting averaged output voltage. This is pulse width modulation.
  • Martin_HMartin_H Posts: 4,051
    edited 2011-02-23 07:56
    Thanks Heater. I suspected it was something like that. But I wasn't sure how to average the PWM output to an analog value.
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