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Old 23rd December 2010, 07:36 PM   #1
dfro is offline dfro  United States
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Default Wiring a 10k fader pot?

I have a simple question. I would like to design a pcb using the following 10k fader pot:

Digi-Key - PP1045SB-ND (Manufacturer - EWA-P12C15B14)

The pot wiper has two pins, 2 and 2', which are on opposite ends of the part. Should I short them together with a pcb trace, or should I just connect to pin 2?

Would shorting them together on the pcb eventually guard against scratchy-ness as the pot wears?

Thanks,
Dave
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Old 23rd December 2010, 08:06 PM   #2
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what are you trying to acheive with it? Are you fading between two inputs, or is it just attentuating one source?
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Old 23rd December 2010, 08:54 PM   #3
dfro is offline dfro  United States
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I am just attenuating one source - actually doing an analog to digital conversion of the wiper voltage level.
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Old 23rd December 2010, 10:03 PM   #4
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I'm presuming your pot is a stereo version. Shorting the 2 and 2' means you now have the two in parallel with resulting change in the effective resistance of the pot.
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Old 24th December 2010, 02:04 AM   #5
benb is offline benb  United States
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The two terminals are surely the same electrical connection, as an ohmmeter will show. Linear slidepots have TWO contacts on the moving part, one that contacts the resistive element, the other that contacts a metal bar. In this Panasonic design pin 2 and pin 2' are connected to this bar at opposite ends of travel. If you're still not sure about this, unbend the little tabs that hold the case on and take the thing apart.

I presume this is done to make for the extra mechanical support of four soldered connections, as well as convenience in where to connect a trace to the wiper, so make sure you have solder pads for all connections and solder them, even if you don't run traces to them all.

So, no, using one or both shouldn't make any difference as far as the pot getting noisy.

The main thing I've heard about keeping pots from going noisy is do not conduct DC current through the wiper (pin 2). This may mean using an opamp buffer circuit to insure a high impedance as seen by the wiper. I might even consider putting a constant AC signal on the input of the pot and measuring the AC level at the wiper to measure the position.

I didn't find any Panasonic info on slider pots other than Digikey's copy of the datasheet, but I found this on Panasonic rotary pots
http://www.panasonic.com/industrial/...AOK0000PE1.pdf
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Old 24th December 2010, 04:15 AM   #6
dfro is offline dfro  United States
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This particular fader pot is not a dual pot. It has a pin 1, pin 2, pin 2', pin 3, four dummy pins that are connected to nothing, and two pins in the middle that are part of the case (I will be attaching these to ground to get some shielding).

An ohm meter shows that 2 and 2' are part of the same 0 ohm strip that is inside the pot.

I agree that 2 and 2' are provided for convenience in creating clean pcb traces. I will just use one of them in my layout.

Thanks, for the link to the pdf.

Dave
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Old 24th December 2010, 05:33 AM   #7
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Having done commercial PCB design your first issue is to get the manufacturer data sheet for hole / pad size and positions and terminal assignments. Those will pretty much tell you how to connect it up. It's really bad to get a board back and find out you screwed hole sizes or pin positions.

One of my more difficult boards was a back plane of a card cage where several of the cards were from other vendors (no tech drawings on these so careful measurements) and connectors were mounted on both sides of the board. 1190 holes, 8 sizes. 4 layers. Less than 100 vias. Double sided silk screen. Feels good when it works.
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