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#### DrWatson

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« on: May 11, 2011, 02:54:06 am »
I was digging through an old box where I found my old 68HC11 kit from years ago when I took a microcontrollers course in college.  I stumbled onto this potentiometer (shown below) and was hoping to recycle it for use on my breadboard learning projects.

It is a Bourns 3355 10k-ohm multiturn trip potentiometer with three leads.  I'm not sure how I'm supposed to hook this up, however.  My brain fails me!  I tried to look for the data sheet, but it looks like it has been retired and is no longer available on the Bourns website (or at least I could not find it).

Any idea what these three leads are, and how I can utilize them as a variable resistor in test circuits?

#### sacherjj

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« Reply #1 on: May 11, 2011, 03:23:14 am »
Potentiometers are almost all the same.  Connections on the edge are the full resistance ends.  The center is the "wiper" that moves between the two ends.

A variable resistor is made when you connect from one edge to the center.  It is generally good practice to short the other side to the center, so if your wiper fails, the highest resistance you will have is the full value of the pot, rather than many meg ohms.

You can also put 5V on one end and ground the other end.  Now the center is a variable voltage divider to play with the A/D convertor on your micro like this:

#### Mechatrommer

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• reassessing directives...
« Reply #2 on: May 11, 2011, 03:24:35 am »
its the common type of anykind brand of potentiometer. left and rightmost pins = fixed ohm at the pot specification, in your case its a fixed 10Kohm. the middle pin is the one who is varying resistance. the construction is here http://en.wikipedia.org/wiki/Potentiometer
if something can select, how cant it be intelligent? if something is intelligent, how cant it exist?

#### insurgent

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« Reply #3 on: May 11, 2011, 04:52:29 am »
Hi DrWatson,

Here's the datasheet that's shows the connections and specs, though it's no different that what most other 3 pin pots are as sacherjj noted above.
http://www.bourns.com/pdfs/3355_obsolete.pdf

#### vk6zgo

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« Reply #4 on: May 11, 2011, 07:31:44 am »
Well,as noted above by previous posters,it isn't a multi-turn pot,it's just a conventional

trim pot,where the two outer connections go to each end of the resistive element,& the

centre connection to the moving contact.

Identifying the connections on real multi-turn pots is not quite so intuitive.

If you are connecting a number of them,it is quite easy to wire one wrong,then copy that

one for the remainder.

Bourns show a circuit on the case of multiturn pots so you don't get confused.

When in doubt,test it with the ohms range on a DMM.

VK6ZGO

#### DrWatson

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« Reply #5 on: May 12, 2011, 09:59:12 pm »
Thank you all for your help.

So if I were wiring this component up on a breadboard and just wanted to use it as a variable resistor, I would hook it up with one terminal and the sweeper terminal as my resistor leads?  Then I would then connect the other terminal to ground and ignore it?

#### sacherjj

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« Reply #6 on: May 12, 2011, 10:51:25 pm »
Thank you all for your help.

So if I were wiring this component up on a breadboard and just wanted to use it as a variable resistor, I would hook it up with one terminal and the sweeper terminal as my resistor leads?  Then I would then connect the other terminal to ground and ignore it?

For just playing around, leave the third terminal connected to nothing.

#### Rufus

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« Reply #7 on: May 12, 2011, 11:15:42 pm »
For just playing around, leave the third terminal connected to nothing.

It is usual to connect the 'third' terminal to the wiper. If the wiper looses contact with the resistive element you get the maximum resistance not an open circuit.

#### DrWatson

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« Reply #8 on: May 13, 2011, 03:12:48 am »
Thanks for the tips.  As suggested I checked it with the multimeter as a sanity check.

Time to get down to work now!

#### sacherjj

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« Reply #9 on: May 13, 2011, 03:27:18 am »
For just playing around, leave the third terminal connected to nothing.

It is usual to connect the 'third' terminal to the wiper. If the wiper looses contact with the resistive element you get the maximum resistance not an open circuit.

That is what I suggested in my first post, but it seemed to add to the confusion.

Smf