Are all "knobs" potentiometers?

Discussion in 'General Electronics Chat' started by Cretin, Jul 5, 2013.

  1. Cretin

    Thread Starter Member

    Dec 13, 2012
    68
    1
    So I used to DJ back in the day, and I had a mixer, with a whole bunch of knobs. I have some little usb powered speakers that have a little groove to adjust for volume that you have to slide back and forth to increase/decrease volume.

    Are all of these in essence potentiometers, adjusting the amount of resistance that affects volume, pitch etc?
     
  2. Shagas

    Active Member

    May 13, 2013
    802
    74
    If they move smoothly then they are most probably Pots and are connected to amplifiers to regulate gain or pitch or whatever(by adjusting resistance.
    If they move in 'steps' then they are most probably Rotary encoders which is a digital way of controlling a parameter.

    Rotary encoder:
    ' A rotary encoder, also called a shaft encoder, is an electro-mechanical device that converts the angular position or motion of a shaft or axle to an analog or digital code.'

    http://en.wikipedia.org/wiki/Rotary_encoder
     
    Cretin likes this.
  3. WBahn

    Moderator

    Mar 31, 2012
    17,715
    4,788
    For the particlular type of application you are talking about, they are probably some kind of rheostat (a variable resistor) or potentiometer (a resistor with an adjustable tap). They don't have to be, particularly in the digital world. Many "knobs" are now simply a shaft encoder (and it can move freely and smoothly and even be spun if that is allowed by the designer) that provides digital pulses to a digital circuit that allow it to keep track of which direction the knob is being turned and by how much.

    But regarding your post title, this is not true of "all knobs". There are lots of cases where a knob is selecting different switch positions or turning a variable capacitor (commonly how older radios were tuned to different stations). I'm sure the list goes on and on, too.
     
    Cretin likes this.
  4. Wendy

    Moderator

    Mar 24, 2008
    20,764
    2,534
    You can also get pots that are laid out as slides, so the final output looks like a spectrum. It is very popular with professional type sets.
     
    Cretin likes this.
  5. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    There are two kinds of pots linear and logarithmic.

    There are also devices that look like pots called attenuators that have zero resistance in the center of rotation but increase resistance going away from center.
     
    Cretin likes this.
  6. Cretin

    Thread Starter Member

    Dec 13, 2012
    68
    1
    A variable capacitor....I've gotta google this!
     
  7. tubeguy

    Well-Known Member

    Nov 3, 2012
    1,157
    197
    There are also pots which have steps like a rotary encoder. This allows repeatable settings. These normally stop at the limits of their rotation like typical pots.
     
  8. Shagas

    Active Member

    May 13, 2013
    802
    74

    Variable caps are usually in the picofarads range but I think special big ones used for radios are maybe in the nanofarads range.

    I found this circuit a while that models a capacitor :

    http://www.falstad.com/circuit/e-capmult.html

    By putting a 100k pot instead of the 100k resistor you can vary the capacitance
     
  9. WBahn

    Moderator

    Mar 31, 2012
    17,715
    4,788
    You can make opamp circuits that mimic either capacitors or inductors using opamps, resistors, and capacitors, but their utility is very limited compared to the real thing by the properties of the opamp. In particular, the frequency at which they behave properly is generally quite low (call it a megahertz, which is being generous is many cases) while a true variable cap or inductor is usable well into the RF range.
     
  10. Shagas

    Active Member

    May 13, 2013
    802
    74
    Yes , forgot to mention that part ,thanks :)
     
  11. wayneh

    Expert

    Sep 9, 2010
    12,087
    3,027
    Televisions used to have knobs to change the channels, and rotary multi-position switches do still exist. So as noted, not all knobs are pots.
     
Loading...