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This might be the noobest question ever, but I'm actually really having trouble understanding at times how to orient a pot from a schematic in the case I don't fully understand the circuit. Maybe I'm just thick as a brick, but I haven't been able to google this satisfactory.

I have made do with just breadboarding and testing or just using front panel mounted pots with the possibility to reverse by a simple twist of the connector, but I really would like to know this better so I can do PCB mounted pots even of circuits I haven't tested on breadboard.

So to exemplify, say I have an ADSR envelope generator and know that I want fully CW to represent long times and CCW short times.

I read a schematic looking like this:

enter image description here

but from the same page I also have an older version (where this part should be identical) where the wiper arrow was pointing the other direction but also connected to the other end-pin:

enter image description here

Both come from http://www.schmitzbits.de/adsr.html

This makes me think that the way the wiper arrow points is the CW side? Is that always so?

Also, at some point I was pretty sure that for straight wiper pins, the right pin when looking from the wiper pin's perspective was always meant to be the CW pin, but now I'm not sure at all.

Just to be clear, I fully know the pinout of my physical pots, that's not the problem. It's just the schematics standard I'm wondering about.

Update:

KiCad's only pot schematic in standard lib looks like this:

enter image description here

Combined with the at least decently common 1(CCW),2(wiper),3(CW) pinout of the physical pots, that plays well with the schematics for this ADSR making the resistance of the rheostat configured pots have max resistance -> longer times when pot is in CW direction.

Can someone confirm similar findings for Eagle standard lib or other standard software? If that is the case, I will at least try to adhere to it myself when drawing a schematic.

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This makes me think that the way the wiper arrow points is the CW side? Is that always so?

In my experience, no.

FWIW, IEEE Std. 315-1975 Graphics Symbols for Electrical and Electronics Diagrams, paragraph 14.2.5 "Rotation description (applied to a resistor)" states that the letters "CW" may be placed at one end of the potentiometer symbol to indicate the "position of adjustable contact at the limit of clockwise travel viewed from the knob or actuator end unless otherwise noted." To create a rheostat from a potentiometer, the designer is free to connect the pot's wiper arm to either end, as deemed appropriate by the designer; there is no requirement to connect the wiper arm to the "CW" end only.

FWIW2, based on my experiences and personal preferences, a best practice when implementing rotary controls like pots, rheostats, quadrature encoders, etc. is this: whenever possible, wire the control so that turning the control's adjustment in a clockwise (CW) direction increases the intended/labeled end effect--increases the amplifier gain, increases the lamp intensity, increases the sound level, etc., and turning it counter-clockwise (CCW) decreases the end effect. That's the assumption most end users, technicians, engineers, etc. will make regarding the control's CW vs. CCW operation. Of course there will be sensible exceptions to this practice. For example, my car's turn signal lever has a rotary control that adjusts the instrument cluster's illumination intensity. That rotary control increases the intensity when I turn it CCW, probably because in that particular orientation turning the knob CCW to increase the intensity just "feels more natural" to the driver.

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  • \$\begingroup\$ Thanks for the reference! The whole second paragraphs only adds bloat though. Of course I want to the pot to behave intuitively, like increased volume CW for a volume pot, that's the reason for my question in the first place. \$\endgroup\$ Nov 22 '17 at 15:18
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In your ADSR example you usually charge and discharge a capacitor to get the envelope. This capacitor is placed where the diodes are connected together. If the charging resistor (attack) is small, you get a fast or short attack. If it is large you get a slow or long attack. Same for the discharging resistor (release).

enter image description here

So, from schematic analysis you usually can determine the correct rotational direction because there is no standard for this.

I faced the same problem a while ago. You do yourself and all others a big favour if you use your schematic to document as much as you can. I decided to put the rotational information within my library symbols so its easier to understand the schematic. I don't care if it is standard or not.

enter image description here

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The IEC standard defines two different symbols for Rheostat and Potentiometer.

enter image description here

What you are referring to is of Rheostat and not of Potentiometer. But there is nothing specified about direction of the rotation for symbole.

References:

http://www.circuitstoday.com/wp-content/uploads/2009/08/Resistor-Electronic-Symbol-with-Notation.jpg

http://www.resistorguide.com/resistor-symbols/

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    \$\begingroup\$ How does this provide any sort of answer to the question? \$\endgroup\$
    – Finbarr
    Nov 20 '17 at 9:39
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    \$\begingroup\$ It is clear that there is no direction defined for rheostat symbol neither for potentiometer symbol by IEC. Although there might be some conventions followed by companies. \$\endgroup\$
    – Vishal P
    Nov 20 '17 at 10:00
  • \$\begingroup\$ "What you are referring to is of Rheostat and not of Potentiometer." Not really since the wiper is actually connected. Pot used as rheostat. \$\endgroup\$ Nov 22 '17 at 15:15
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As this is presumably from an analog synthesizer, which uses voltage levels to control the gain of the ADSR block, it's safe to assume that the junction of the three diodes (in the top diagram) and the two 220 Ohm resistors (in the bottom diagram) has a capacitor connected to ground. The variable resistors control the rate at which the capacitor is charged and discharged and hence the attack and release times of the envelope; the higher the resistance the longer the time it takes to charge or discharge the capacitor.

So you would wire your pots in such a way that the highest resistance is used when the pot is fully clockwise. If necessary, check this with an ohmmeter.

enter image description here

If your pot looks something like this (front view) you would connect terminals 2 and 3 together to one of the connection points in your schematic and terminal 1 to the other, it doesn't matter which way round.

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  • \$\begingroup\$ "This makes me think that the way the wiper arrow points is the CW side? Is that always so?" -> "So you would wire your pots in such a way that the highest resistance is used when the pot is fully clockwise. If necessary, check this with an ohmmeter." - Okay. \$\endgroup\$ Nov 20 '17 at 9:47
  • \$\begingroup\$ In this case, both diagrams actually show the wiper pointing to the CCW side, but I would never trust that being any sort of standard. \$\endgroup\$
    – Finbarr
    Nov 20 '17 at 9:58
  • \$\begingroup\$ I'll do the last copy and paste here that OP said. "Just to be clear, I fully know the pinout of my physical pots, that's not the problem. It's just the schematics standard I'm wondering about." - In other words, the question is regarding the arrows in the schematics. - Your answer does not answer question.. at all. - I know, sometimes you just misread a question or misunderstand 150%, it happens. \$\endgroup\$ Nov 20 '17 at 10:08
  • \$\begingroup\$ @HarrySvensson The question is about translating a schematic into a physical implementation. I'm saying that you need to understand how the circuit works in order to be sure of getting that right. \$\endgroup\$
    – Finbarr
    Nov 20 '17 at 11:38
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    \$\begingroup\$ @Finbarr Actually, your last comment makes your opinion much more clear than your whole post. That should be the first sentence of your post. Then you can proceed on explaining how to interpret the circuit to get that right. \$\endgroup\$
    – dim
    Nov 22 '17 at 15:23

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