Using a potentiometer(pot)

So another one of the items that came in my kit was a potentiometer often shortened to pot (Im already sick of typing potentiometer so it will be pot from here on out).  The pot is an interesting device that acts as a variable voltage divider or simply a variable resistor.  Let’s take a look so you can see what I mean…

A couple of things to notice here.  First – notice the position of the arrow on the top of the pot.  Also notice that there are only two wires connecting to the pot at this time.  As you can see in the top picture of this post, the pot has 3 leads available for us to use so we’re only using two of them.  Now let’s turn the knob on our pot and see what happens…

Now notice the position of the arrow on the pot and the new current reading on the multimeter.  So what’s happening?  In this configuration, the pot is acting as a true variable resistor.  By turning the knob on the pot we can increase and decrease the resistance of the pot.  In my case, these are 10k ohm pots meaning that in their max position they can provide 10k ohms worth of resistance.  So that’s pretty straight forward, but what do we use the third lead for?

When we use the third lead, we’re actually turning the pot into a variable voltage divider.  Recall from my last post that a voltage divider was a simple circuit type designed to increase or decrease the voltage output.  So let’s rearrange the board a little bit…

In this case, we’ve taken the LED out of the circuit entirely and just left the multimeter plugged in.  Typically, this would mean that we’d be measuring the voltage drop of the circuit but since theres nothing in this circuit, we should be getting 5 volts.  In this case – we’re not since I’ve reconfigured the pot to use all three leads and act as a voltage divider.  That is, the voltage it’s providing to the multimeter is being lowered due to the pot acting as voltage divider. If we remove the lead connecting the pot to ground we can see that it goes back to acting as a resistor instantly…

And as expected we get 5 volts again.  Why is this?  Because with a resistor inline we’re just measuring the total voltage in the circuit.  When the pot acts as a voltage divider we change the actual voltage being presented to the multimeter.

Im not sure how handy pots will be in the experiments I plan on doing but I can see there relevance with certain types of circuits.

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