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I'm having difficulty finding how to connect a potentiometer. In circuits potentiometer has only 2 pins like a resistor, however in real life it has 3 pins. Please help me!
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http://www.arduino.cc/en/Tutorial/Potentiometer
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I don't think you connected the grounds, Dave.
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In circuits potentiometer has only 2 pins like a resistor
It may be that the potentiometer is intended to be wired as a variable resistor, and not a potential divider, but without seeing the circuit, it is difficult to know (hint).
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In circuits potentiometer has only 2 pins like a resistor
It may be that the potentiometer is intended to be wired as a variable resistor, and not a potential divider, but without seeing the circuit, it is difficult to know (hint).

I know how to connect a pot meter to arduino, but my doubt is about connecting it in normal circuits. For example the second circuit found on this web page http://www.buildcircuit.com/darklight-sensor-using-transistor/
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Never mind I figured it out. To use pot meter as variable resistor you have to leave one of the end pins unconnected and use the other two. smiley-wink
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I'm having difficulty finding how to connect a potentiometer. In circuits potentiometer has only 2 pins like a resistor, however in real life it has 3 pins. Please help me!
You are confusing two different devices.  A potentiometer has three pins, it is essentially a fixed resistor with a variable tap.  A rheostat has two pins, it is essentially a variable resistor.

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Never mind I figured it out. To use pot meter as variable resistor you have to leave one of the end pins unconnected and use the other two.
This will frequently work in electronic circuits.  Most of the time one end is connected to the wiper as shown in the circuit diagram you mentioned.  In either case you should be aware that you are in danger of destroying the potentiometer when you adjust it toward one end if you don't have a fixed resistor in series with it.

As you adjust the potentiometer toward the low resistance end of it's travel the current increases.  In the absence of a external series resistance just before you get to zero ohms you have slightly less than infinite current.  This is the reason that many potentiometers are burned out at one end.


From the tutorial at the link in reply #1:  "A potentiometer is a simple knob that provides a variable resistance..." 
My opinion: AARRGGHH


Don
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It was, and probably still is, good practice to connect the "redundant" third terminal of a potentiometer to the slider terminal when using as a rheostat.  By that means, if the slider connection to the track should fail, the rheostat value goes to the full resistance value rather than open circuit.
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