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We all know its customary for a VOLUME control on any audio product should require turning CW to make it louder. In fact for user accessible rotary adjustments, clockwise almost universally means "more". This despite the fact that all plumbing faucets do the opposite. But it seems whenever I design a circuit where a trimpot makes the most sense, I'm always self debating this, and even when I reach what I think is a sensible decision I often find I'm later second guessing myself.

Consider, for example a trim pot that limits the maximum GAIN in an amplifier. On the one hand, it would seem to follow the "volume control" logic that CW should be more gain. But then again when you make adjustments looking at a schematic, sometimes it seems like the opposite might make more sense. Especially when only 2 legs of the trimmer is used, maybe CW should always mean more resistance.

I doubt there is a right or wrong to this, so I always try to notate my schematics with an arrow near the trim pot wiper with either "CW" or "CCW". Right or wrong, that way at least I know what to expect. But for as many times as the final adjustment direction didn't seem to make as much sense as I thought it would on paper, I thought it might be interesting to see if there is some consensus or set of conventions, as there already is for user level adjustments.

Randy
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    I don't know where you live but faucets turn CW for MORE here... although we do have Hot Faucets that go the other way and confuse the heck out of people. – Trevor_G Mar 20 '17 at 19:17
  • Just make sure nothing goes wrong when you put it to either maximum or minimum. People don't get left and right, I wouldn't expect them to get CW or CCW either. (I probably will never learn where east and west is for some strange reason) – Arsenal Mar 20 '17 at 19:24
  • Well "go wrong" is a relative term. I re thought all this having some "gain limit" trimpots on a PC board. If set wrong, it could mean excessive feedback, or erring the other way it would prevent maximum usable volume. But in either case, nothing will catch fire. :-) – Randy Mar 20 '17 at 19:39
  • Yeah that's what I meant with go wrong. The device must still be recoverable (i.e. turning the pot to a correct value) even if it was at the maximum values. – Arsenal Mar 20 '17 at 19:52

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It seems logical to my way of thinking that CW is "forward , up, and more" of any parameter you are adjusting such as Black Level or White level which are opposites or simply "more resistance" using pins 1 & 2.

The pins should be numbered "one TWO three " which also is to say the CW direction of wiper rotation from 1 TO 3. That's always been a Bourns® standard.

;)

Tony Stewart EE75
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  • Just for S's and G's, what do you think of the situation I mentioned in comment. The purpose of the trim is "Gain Limit". It is an audio situation, actually to optimize a "compressor/limiter". So one can hear the result of an adjustment. But.. more "gain" will allow the user volume control to amplify a bit MORE, but more "limit" will do the opposite. I believe I decided the CW direction would mean more "limit", but less max "volume" when the compressor/limiter is turned on. Made sense at the time, but whenever I adjust it, I find myself re-thinking my choice. So I guess I agree with you. LOL! – Randy Mar 21 '17 at 17:33
  • glad you see the logic of expected outcome. – Tony Stewart EE75 Mar 21 '17 at 18:42
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In my opinion, in general CW should mean "adjust up" when you are checking something on the scope or have some other measurable or visible effect (by whatever human senses apply).

Sometimes though, when it's a mixing / "either or" proposition, the direction can get complicated.

Trevor_G
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  • Yeah, that's just the kind of situation that made me rethink this question. I have a circuit with two trim adjustments whose purposes are related to "gain limit", and despite my CW arrows and copious notes on the schematic, I find myself going the wrong way every time I go to calibrate one. Based on other circuits I've seen, either there is no universal set of rules, or nobody is following them. :-) – Randy Mar 20 '17 at 19:35
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    @Randy, in the end there is no substitute to actually building a prototype and personally doing a few calibrations and seeing if the "wrong-way" issue keeps recurring. Maybe even getting a few folks to try. If it does, then reverse it. – Trevor_G Mar 20 '17 at 19:41
  • And double trim is always a nightmare @Randy – Trevor_G Mar 20 '17 at 19:43