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Unread 25-01-2013, 16:30
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Wiring A Potentiometer

I wired a potentiometer to the analog breakout, I am reading voltage from it in Windriver c++ but for some reason the analog breakout gets extremely hot and the green light on the analog breakout turns off anytime the knob on the pot is turned all the way down.
did I wire it wrong or something?
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Unread 25-01-2013, 16:32
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Re: Wiring A Potentiometer

Quote:
Originally Posted by krudeboy51 View Post
I wired a potentiometer to the analog breakout, I am reading voltage from it in Windriver c++ but for some reason the analog breakout gets extremely hot and the green light on the analog breakout turns off anytime the knob on the pot is turned all the way down.
did I wire it wrong or something?
Post the part number of the pot, and a close-up picture of the wiring (at both the pot end and the analog breakout end).


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Unread 25-01-2013, 16:34
Jim Wilks Jim Wilks is offline
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Re: Wiring A Potentiometer

Quote:
Originally Posted by krudeboy51 View Post
I wired a potentiometer to the analog breakout, I am reading voltage from it in Windriver c++ but for some reason the analog breakout gets extremely hot and the green light on the analog breakout turns off anytime the knob on the pot is turned all the way down.
did I wire it wrong or something?
Sounds like it's wired wrong. Power it down. Let's see a sketch of what you have.
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Unread 25-01-2013, 16:57
s1900ahon s1900ahon is offline
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Re: Wiring A Potentiometer

Occam's Razor suggests "yes, you likely wired it wrong"

Potentiometers have 3 terminals, two between the ends of a resistor and one that contacts the resistor between the ends (typically controlled by the shaft).

If you have a 5kohm pot, there is 5kohms between the two ends, regardless of the shaft angle, and the resistance between either end and the wiper varies based on shaft angle.

You connect the two ends across power and ground (red and black) and connect the wiper to the signal (white) [respective to a white-red-black servo wire]

What it sounds like is you wired power and ground to one end and the wiper. As you rotate the wiper towards one end, the resistance goes down, current goes up, and eventually the supply craters due to excessive current draw.
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Unread 25-01-2013, 17:01
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Re: Wiring A Potentiometer

http://imgh.us/DSC_00601.jpg

Underneath the pot, it marked "D5K"

Thanks, I re-wired it properly this time, I confused with the whole resistance distribution and location of the wiper

Last edited by krudeboy51 : 25-01-2013 at 17:21.
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Unread 25-01-2013, 17:21
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Re: Wiring A Potentiometer

Quote:
Originally Posted by krudeboy51 View Post
http://imgh.us/DSC_00601.jpg

Underneath the pot, it marked "D5K"
Now we need to see where the red, white, and black wires are connected on the other end:

Quote:
Originally Posted by Ether View Post
and a close-up picture of the wiring (at both the pot end and the analog breakout end).
... If the red wire is power, that is INCORRECT.

BTW, you need to get rid of those wire whiskers.

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Unread 25-01-2013, 17:42
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Re: Wiring A Potentiometer

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Originally Posted by Ether View Post
BTW, you need to get rid of those wire whiskers.
Seriously, have someone take a closer look at that. It's asking for trouble. You'd be well advised to inspect all the other solder joints (and crimps) on the robot too.


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Unread 25-01-2013, 18:38
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Re: Wiring A Potentiometer

I agree with Ether. That soldering job is pretty rough looking, and yes, in competition, I would expect to see smoke emitting from it at some point.

Invest in some soldering flux, leaded solder (60/40 with rosin core is my favorite), and some heat shrink.

Remember to put the heat shrink on the wire before you solder it, and make sure it is away from the soldering point while soldering, because it will shrink down with very little heat. I know this seems like common sense, but I can't count how many times I've done it, and I will guarantee that I will do it again in the future.

Leaded solder, of course, has lead in it. No, you won't get any diseases from using it, but you should thoroughly wash your hands with soap and hot water, ESPECIALLY before eating.

Here's how to properly solder, or at least my preferred way, and I'm pretty good if I do say so myself.

Apply a small dab of flux to the terminal and wire after you feed it through the potentiometer holes (again, don't forget the heat shrink!!!). If you get too much flux on, that's fine. The more, the better... err... you won't hurt anything by having too much.

Apply a small bit of solder to the iron. This will be used JUST to help aid in heat transfer.

Touch the iron to the terminal and allow it to heat for a few seconds (2 or 3 seconds should suffice). Solder won't bond unless both the wire and terminal are heated up enough. You'll notice the solder you applied to the iron 'flow' to the terminal once it's hot enough.

At this point, feed some more solder in to make a nice, smooth joint.

Inspect the solder joint for any bubbles, cracks, or anything out of the ordinary.

Allow the joints to cool, and then slide the heat shrink over the terminals to insulate them.

Use a heat gun to shrink the heat shrink. If you don't have one, you can use a flame of some sort, but be quick and spread the heat. Heat shrink, like anything else, will catch on fire if it gets hot enough.

If you don't have heat shrink, then insulate it with electrical tape. Just insulate it somehow. Signal wires are a magnet for shorting.
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Unread 25-01-2013, 18:54
s1900ahon s1900ahon is offline
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Re: Wiring A Potentiometer

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Originally Posted by RyanN View Post
You'll notice the solder you applied to the iron 'flow' to the terminal once it's hot enough.
(Bold emphasis mine.)

Interestingly, the origin of the word flux, fluxus from Latin, meaning "to flow".

-Scott
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Unread 25-01-2013, 21:41
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Re: Wiring A Potentiometer

Quote:
Originally Posted by s1900ahon View Post
(Bold emphasis mine.)

Interestingly, the origin of the word flux, fluxus from Latin, meaning "to flow".

-Scott
Nice! I was never curious enough about it, but now I know.
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Unread 25-01-2013, 22:56
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Re: Wiring A Potentiometer

Swap the red and white wires.

-Hugh
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