where use all three terminals on a potentiometer?

[layoutdesign]

I have used two of the three terminals to vary the resistance for
controling the gain or amplification for audio. I am newbie and
haven't used the three terminals all at the same time. I guess it
might be used to split current or perhaps some usage for varying the
voltage drop? Is there any circuit for hobbyist to build to use all
three terminals for some sort of cool device?

 

[Tim Wescott]

layoutdesign wrote:

I have used two of the three terminals to vary the resistance for
controling the gain or amplification for audio. I am newbie and
haven't used the three terminals all at the same time. I guess it
might be used to split current or perhaps some usage for varying the
voltage drop? Is there any circuit for hobbyist to build to use all
three terminals for some sort of cool device?

The "right" way to use a potentiometer for a volume control is to
connect the output of your preamp stage to the 'top' of the pot, connect
the 'bottom' to ground, and take the audio off of the tap.

Similarly, if you want to use a potentiometer for a position feedback,
you would power the top and bottom terminals with either +V and ground,
or +V and -V, and take the position reading off of the tap. Using the
+V/-V method means that the tap voltage is proportional to the (signed)
position around center, where the +V/0V method means you have to
interpret the position as having one sign, or you have to add in an
offset yourself.

Start paying attention to circuit design projects on web pages or in
magazines, and you'll see this.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

 

[Eeyore]

layoutdesign wrote:

I have used two of the three terminals to vary the resistance for
controling the gain or amplification for audio. I am newbie and
haven't used the three terminals all at the same time. I guess it
might be used to split current or perhaps some usage for varying the
voltage drop? Is there any circuit for hobbyist to build to use all
three terminals for some sort of cool device?

You use all 3 terminals for a potentiometer, most popularly in your
instance as a volume control.

Using only 2 terminals as a volume control will result in a limited
range that will never be fully off.

Graham

 

[JeffM]

layoutdesign wrote:

I have used two of the three terminals to vary the resistance for
controling the gain or amplification for audio.

This describes the simplest example of a "pad". It is VERY dependent

on the impedances of *other* elements in the circuit.
(With a "pot", you want that other stuff to be "swamped out".)

....and if you're only using 2 terminals, you're using the wrong term:
http://www.google.com/search?q=A.rheostat.is.a.two-terminal.variable.resistor

Here is the fundamental concept of a potentiometer
(without the fancy name).
http://www.google.com/search?q=cache:L_MdVwVuYzoJ:en.wikipedia.org/wiki/Voltage_divider+gnu+potentiometer&strip=1

 

[terryS]

On Jun 2, 9:43 pm, layoutdesign <ford...@gmail.com> wrote:

I have used two of the three terminals to vary the resistance for
controling the gain or amplification for audio. I am newbie and
haven't used the three terminals all at the same time. I guess it
might be used to split current or perhaps some usage for varying the
voltage drop? Is there any circuit for hobbyist to build to use all
three terminals for some sort of cool device?

xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

Think of it as voltage divider. In some instances that can be an
oversimplification but helps understanding.

Across the two ends connect the full input voltage. Let's say (for
sake of argument that is ten volts).

Between one end and the 'slider' the movable connection. You will get
a voltage which depends on the location/position of the movable
connection.

As an example you would expect that if half-way one would get say 5
volts!

What you actually get depends how the resistance varies across the
approx. 270 degree rotation. (of a circular 'Pot'). The variation is
sometimes referred to as 'taper'.

An older name for them is potentiometer; meaning you can adjust and
measure the output voltage

The potentiometer has to fit into (MATCH) the type of circuit in which
it is used. One could not for example connect a half megohm
'potentiometer' into a 4 ohm speaker circuit and expect to do anything
but give full volume to a speaker, at maximum setting!!!! And probably
not much elsewhere the moment the 'pot' is turned away from maximum.

Any help?