Potentiometer leads - Page 1
Forum section: electronics / beginners

author: DrWatson
author_rank: Newbie
timestamp: May 11, 2011, 02:54:06 am
content: 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?

author: sacherjj
author_rank: Frequent Contributor
timestamp: May 11, 2011, 03:23:14 am
content: 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:

author: Mechatrommer
author_rank: Super Contributor
timestamp: May 11, 2011, 03:24:35 am
content: 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 herehttp://en.wikipedia.org/wiki/Potentiometer

author: insurgent
author_rank: Regular Contributor
timestamp: May 11, 2011, 04:52:29 am
content: 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

author: vk6zgo
author_rank: Super Contributor
timestamp: May 11, 2011, 07:31:44 am
content: Well,as noted above by previous posters,it isn't a multi-turn pot,it's just a conventionaltrim pot,where the two outer connections go to each end of the resistive element,& thecentre connection to the moving contact.Identifying the connections onrealmulti-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 thatone 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

author: DrWatson
author_rank: Newbie
timestamp: May 12, 2011, 09:59:12 pm
content: 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?

author: sacherjj
author_rank: Frequent Contributor
timestamp: May 12, 2011, 10:51:25 pm
content: Quote from: DrWatson on May 12, 2011, 09:59:12 pmFor just playing around, leave the third terminal connected to nothing.

author: Rufus
author_rank: Super Contributor
timestamp: May 12, 2011, 11:15:42 pm
content: Quote from: sacherjj on May 12, 2011, 10:51:25 pmIt 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.

author: DrWatson
author_rank: Newbie
timestamp: May 13, 2011, 03:12:48 am
content: Thanks for the tips. As suggested I checked it with the multimeter as a sanity check.Time to get down to work now!

author: sacherjj
author_rank: Frequent Contributor
timestamp: May 13, 2011, 03:27:18 am
content: Quote from: Rufus on May 12, 2011, 11:15:42 pmThat is what I suggested in my first post, but it seemed to add to the confusion.