My Analogue inputs (Pots) have very fine range of adjustment.

OLDmarty

Senior Member
Hi All,

I built a small pot-box test jig recently.
It has 8x 10K pots in the box, with all the pot-ends wired to 5v and 0v accordingly, then the 8x wipers connect to a 40X2 picaxe on all 8 bits of Port-D (set to analogue inputs).

An older sketch of just 4 pots wired into my picaxe, just to clarify my wiring (x8):
23191
While my test code works, there doesn't seem to be much physical range on my pots

I have a strong feeling that the 8x 10K pots (basically paralleled) has now made each pot appear as a 1.2k pot into the A-D pin.
Maybe i should raise all my pots to 50K so the final value is approx 6.2k, giving more voltage range across the pot movement?
(or 8x 100K pots, giving a 12.5k total).


I have used a quick 'lookup' code to test the concept.

Code:
Symbol Pot_1 = b0
Symbol LEDPort = outpinsB

do

     readadc 20, Pot_1    ; Read Pot#1 connected to the Port D.0 pin
     Pot_1=Pot_1/16    ; divide pot into ranges of "16" (256/16='16' zones of the physical pot rotation where each value will change.
     lookup Pot_1,($00,$08,$04,$02,$01,$0C,$06,$03,$09,$0A,$05,$0E,$07,$0B,$0D,$0F),LEDport    ;Load value into LEDport for the testing on some LEDS.

loop
Using the above code, the beginning of the pot rotation does nothing for about 10mm of rotation, then the lookup data starts appearing on my Port B LEDs.
At this time, basically each 1mm of pot movement will advance to the next lookup data, and after the last data is displayed, there's a further 10mm of travel before the pot reaches it's physical end point.

I thought that dividing the A-D range of 0-255 into 16 'zones' would spread quite evenly across the travel of the pot.
Even if i use 10bit ADC, it's the same effect with pot rotation not being spread out evenly.

I have then replaced the 'lookup' code with a 'select case' method (below), to create 16x evenly spaced pot 'zones', but the pot still bahaves the same way, all the action in the central area of the pot, but nothing on the ends.

I changed code to read each of the 8 pots, so i know the pot(s) aren't faulty, they all respond the same way.

Should i be using a different way to zone my pot range? or just replacing the pots to much higher values?

Thanks in advance...

Code:
select case Pot_1

    case 0 to 15            ; if "Pot_Speed" value is within this range, then
        LEDport = $00        ;output this data on Cport LSB 4 bits to LEDs
    case 16 to 31            ; if "Pot_Speed" value is within this range, then
        LEDport = $08        ;output this data on Cport LSB 4 bits to LEDs
    case 32 to 47            ; if "Pot_Speed" value is within this range, then
        LEDport = $04        ;output this data on Cport LSB 4 bits to LEDs
    case 48 to 63            ; if "Pot_Speed" value is within this range, then
        LEDport = $02        ;output this data on Cport LSB 4 bits to LEDs
    case 64 to 79            ; if "Pot_Speed" value is within this range, then
        LEDport = $01        ;output this data on Cport LSB 4 bits to LEDs
    case 80 to 95            ; if "Pot_Speed" value is within this range, then
        LEDport = $0C        ;output this data on Cport LSB 4 bits to LEDs
    case 96 to 111            ; if "Pot_Speed" value is within this range, then
        LEDport = $06        ;output this data on Cport LSB 4 bits to LEDs
    case 112 to 127            ; if "Pot_Speed" value is within this range, then
        LEDport = $03        ;output this data on Cport LSB 4 bits to LEDs
    case 128 to 143            ; if "Pot_Speed" value is within this range, then
        LEDport = $09        ;output this data on Cport LSB 4 bits to LEDs
    case 144 to 159            ; if "Pot_Speed" value is within this range, then
        LEDport = $0A        ;output this data on Cport LSB 4 bits to LEDs
    case 160 to 175            ; if "Pot_Speed" value is within this range, then
        LEDport = $05        ;output this data on Cport LSB 4 bits to LEDs
    case 176 to 191            ; if "Pot_Speed" value is within this range, then
        LEDport = $0E        ;output this data on Cport LSB 4 bits to LEDs
    case 192 to 207            ; if "Pot_Speed" value is within this range, then
        LEDport = $07        ;output this data on Cport LSB 4 bits to LEDs
    case 208 to 223            ; if "Pot_Speed" value is within this range, then
        LEDport = $0B        ;output this data on Cport LSB 4 bits to LEDs
    case 224 to 239            ; if "Pot_Speed" value is within this range, then
        LEDport = $0D        ;output this data on Cport LSB 4 bits to LEDs
    case 240 to 255            ; if "Pot_Speed" value is within this range, then
        LEDport = $0F        ;output this data on Cport LSB 4 bits to LEDs


    endselect
 
Last edited:

premelec

Senior Member
Do you have a multimeter? Test the actual output of the wiper as connected - paralleling the pots should not affect their output characteristic unless you have a 'soft' [high impedance] 5 volt power supply which will then draw down the actual voltage from 5v - also the SAME supply to the pots must connect to the PICAXE as the measurement is ratiometric...
 

OLDmarty

Senior Member
Do you have a multimeter? Test the actual output of the wiper as connected - paralleling the pots should not affect their output characteristic unless you have a 'soft' [high impedance] 5 volt power supply which will then draw down the actual voltage from 5v - also the SAME supply to the pots must connect to the PICAXE as the measurement is ratiometric...
Yes, all 8 wipers are working correctly, i can see 0 to 255 when i open the terminal window.

The 5volt supply has 3 amp capacity, no problems there.
 

OLDmarty

Senior Member
Judging by what you have observed, it appears to me that your pots have a logarithmic or audio taper, where the resistance is 'crowded' at one end of the resistive track.

Unfortunately, the markings on the pot will vary depending on where in the world the component is manufactured. This page may help give you an understanding.
Yep, i thought they might be LOG too, but the pot body is clearly stamped "10K B" on the body (LINEAR).

Unless, chinese manufacturers are (accidently?) inserting LOG inserts inside LINEAR (marked) bodies :-(
 

depeet

New Member
I could be wrong, but I think that you can not make a variable out of the outpinsB like you did with Symbol LedPort = outpinsB

Since you see the correct values in the terminal, the potentiometers should work correctly. In your case routine, I would go this way and see if this resolves your problem. your line with Symbol LedPort = outpinsB can be deleted

Code:
select case Pot_1
    case 0 to 15
    let OutpinsB = $00
        case 16 to 31
    let OutpinsB = $08
    .
    .
    .
 
Last edited:

OLDmarty

Senior Member
I could be wrong, but I think that you can not make a variable out of the outpinsB like you did with Symbol LedPort = outpinsB

Since you see the correct values in the terminal, the potentiometers should work correctly. In your case routine, I would go this way and see if this resolves your problem. your line with Symbol LedPort = outpinsB can be deleted

Code:
select case Pot_1
    case 0 to 15
    let OutpinsB = $00
        case 16 to 31
    let OutpinsB = $08
    .
    .
    .
Sorry, i may have shorthanded some of my code, i was putting together some of it, off the top of my head, but basically i would have done something like "Symbol LedPort B0" and then later in the code i must have used something like OutpinsB = LedPort" etc.

The FACT is, the code i'm using in Orig post is working code, but i'm not happy with the narrow physical range of the pot.

Yes, the Terminal does show every pot is working from 0 to 255, but this still doesn't mean it's a spread/linear range of numbers......I'm sure if i examine the Temrinal window next time, the '0' value will stay current for the first 10mm of pot travel, follow by a range of changing numbers, then it'll stick on '255' for the last 10mm of pot travel which is the whole point of my OP.

Besides using LEDs on a port, i'd also made it send the lookup table via i2c to a LED Matric display. This ALSO fails to track across the entire range of the pot movement.

I either have a problem with the pot values in parallel upsetting the linear range, or, there's still a problem with the A-D, or lack of A-D config settings.
Maybe i need to use ADC calib setting? but from what i read, i don't need it.
 

hippy

Senior Member
Some pots can have 'dead zones' at each end due to the way the tracks are manufactured but, in this case, those dead zones seem excessively large compared to the size of the resistance segments -

Code:
0V   _____ _ _ _ _ _ _ _ _ _ _ _ _____   5V
----|_____|_|_|_|_|_|_|_|_|_|_|_|_____|----
    /|\                             
     |
The pure metal, same resistance, end sections can be seen in this photograph -

http://www.imajeenyus.com/electronics/20111018_potentiometer_end_stop_mod/photos/DSCN4938.JPG

As can be seen though; the same resistance sections are nowhere near a quarter of the track length.

Normally physical end stops on a pot will prevent excessive wiper travel along the same resistance sections but preset pots may allow more because they are only adjusted once.

I would suggest mapping out what raw values and zoned values you get when the pot is set to zero and then turned, see what that shows up -

Code:
Do
  ReadAdc 20, b0
  b1 = b0 / 16
  SerTxd( #b0, TAB, #b1, CR, LF )
  Pause 250
Loop
 

OLDmarty

Senior Member
Some pots can have 'dead zones' at each end due to the way the tracks are manufactured but, in this case, those dead zones seem excessively large compared to the size of the resistance segments -

Code:
0V   _____ _ _ _ _ _ _ _ _ _ _ _ _____   5V
----|_____|_|_|_|_|_|_|_|_|_|_|_|_____|----
    /|\                            
     |
The pure metal, same resistance, end sections can be seen in this photograph -

http://www.imajeenyus.com/electronics/20111018_potentiometer_end_stop_mod/photos/DSCN4938.JPG

As can be seen though; the same resistance sections are nowhere near a quarter of the track length.

Normally physical end stops on a pot will prevent excessive wiper travel along the same resistance sections but preset pots may allow more because they are only adjusted once.

I would suggest mapping out what raw values and zoned values you get when the pot is set to zero and then turned, see what that shows up -

Code:
Do
  ReadAdc 20, b0
  b1 = b0 / 16
  SerTxd( #b0, TAB, #b1, CR, LF )
  Pause 250
Loop
Thanks Hippy, i'll try your test code when i'm back at the workshop.

Looking at the photo of the carbon track on that pot, if you can imagine a further 10mm of missing carbon on EACH end, then that's how my pots appear to be responding. If the active carbon range is 270degrees, then i reckon my pot(s) are closer to 180degrees effective carbon track.

I'll log some figures tomorrow, and see what it tells me about the exact pot activity.
 

inglewoodpete

Senior Member
Ultimately, what does a multimeter say about the voltage on the wiper as it is rotated? If the voltage aligns (proportionately) with the PICAXE's readings, then the issue is in the potentiometer hardware.
 

hippy

Senior Member
If the active carbon range is 270degrees, then i reckon my pot(s) are closer to 180degrees effective carbon track.
It could be these are just 'badly made' pots or not intended for the purpose being used.

Are they traditional pots with a shaft and push-on knob shaft, or preset pots, perhaps preset with a small knob pre-fitted to them ? Do you have a part number or link to supplier or manufacturer ?

If it does look like there's only 180-degree of useful travel you might have to sacrifice one, open it up to confirm how it is inside. A multi-meter test as inglewoodpete suggests or test program should however reveal much of what is going on.
 

geezer88

Senior Member
I would use a voltmeter to measure a few of the pots at 0, 25, 50, and 100% of rotation. Just by eye you should be able to see if there is something goofy with the pots. Wouldn't take more than ten minutes to do several. This would quickly sort out linear from log from big dead band at beginning or end of rotation. Interesting problem, I'll enjoy hearing what it turns out to be.

tom
 

OLDmarty

Senior Member
Hi all,

OK i opened one of my spare pots today and the carbon track seems to be the regular coverage as expected.
(FYI: these are DUAL 10k Linear pots, but i'm only using one half of the stereo pots in my picaxe test-jig project).

Note that the pot isn't labelled ALPS or ALPHA etc, these just seem to be chinese ebay knock-offs.

23192

23193


23194
 

OLDmarty

Senior Member
Hi again,

OK, Here's some pot voltage measurements...

The voltage at the pot-ends are 0v and 5.178 volts (stable).

Interesting to note, that at the pot-ends, it only takes about 2mm of movement from either end stop to begin a change in wiper voltage readings as compared to the code where it appears to be 10mm of travel before a change occurs from either end-stop.

ALL 8x pots measure as follows...
1) At the 0v end, 2mm travel from the end-stop changes from 0v to 10 millivolts and scales upward with wiper travel.
2) At the 9 0'clock position, the wiper is approx 180 millivolts
3) At the 12 o'clock (centre) position, the wiper is 2.5v to 2.6v (+/- 100 millivolts), based roughly on my knob being fitted exactly central (or not).
4) At the 3 0'clock position, the wiper is approx 4.9v
5) At the 5v (5.178v) end, 2mm travel from the end-stop changes from 5.178v to 5.168 volts and scales downward with wiper travel.

FYI: ALL voltages above are identical when measured on the picaxe pins too.
(there is approx 1 metre of ribbon cable between pot-box test jig and the picaxe board, but no voltage losses).


The pots being measured are the pots in my actual "pot-box" test jig.
When this jig is plugged into my 40X2, it seems the LEDS don't start changing patterns until the wiper is moved approx 10mm from either pot end, and as i said earlier, it's only the central 180 degrees of pot movement that seems to cause the LEDs to change with each 1mm movement.
(i was hoping the segmenting of my lookup table (or select case) would evenly distribute the LED patterns across the entire pot range).
 

geezer88

Senior Member
In the top photo, number 1 position, righthand end you can see the metallic material extends almost to the 3 o'clock position. I can't tell on the other end, but I bet it is the same based on your measurements. I think you have gotten some special pots with linear taper and 180 degree active portion. I have never seen such a specimen. Maybe a balance control on a stereo system. I guess your options are live with them as is, but regulars, or figure out a way to mechanically limit rotation to the active range.
tom
 

OLDmarty

Senior Member
In the top photo, number 1 position, righthand end you can see the metallic material extends almost to the 3 o'clock position. I can't tell on the other end, but I bet it is the same based on your measurements. I think you have gotten some special pots with linear taper and 180 degree active portion. I have never seen such a specimen. Maybe a balance control on a stereo system. I guess your options are live with them as is, but regulars, or figure out a way to mechanically limit rotation to the active range.
tom
It's just a surface scratch from pulling it apart.

The carbon track measures from the 7 o'clock point (left) all the way around to the 5 o'clock position (right).
 

hippy

Senior Member
It does seem odd. "B10K" should be linear, and 2.5V at 12 o'clock would seem to confirm that. At 3 o'clock and 9 o'clock the pots should be about 2/3rds of the way between 12 o'clock and the end stops. So those should be about 0.8V and 4.2V.

I did think that maybe the two wipers aren't aligned with each other, are offset to give some sort of better result when used as balance controls but 2.5V at 12 o'clock would seem to discount that, Might be worth measuring the other pot wafer to see if the voltages on each track each other but I suspect they will.

I can only think these are some sort of weird linear-log combination, or have been badly made but that seems unlikely, that it's more by design.

It could well be that 180-degree travel is what is ideal for audio balance pots so that's what they are.
 

AllyCat

Senior Member
Hi,
The carbon track measures [?] from the 7 o'clock point (left) all the way around to the 5 o'clock position (right).
Yes it "continues" between those points but, as Tom suggested in #15, the "metal" layer appears to continue as far underneath the carbon track as it extends beyond the track to the "pins". The bulk conductivity of the track material is probably quite low (perhaps only tens of ohms across the faces of a small "cube") because the track is long, narrow and thin to make up the 10k. So the resistance between the "top" and "bottom" faces of the track will be low.

Try measuring the resistance of the pot (track), perhaps even probing the track itself if your multimeter has pointed probes.

Cheers, Alan.
 
Last edited:

techElder

Well-known member
Try measuring the resistance of the pot (track)
OLDMarty, you've spent enough time on those pots without actually gathering enough data to produce a chart of resistance vs. rotation.

2) At the 9 0'clock position, the wiper is approx 180 millivolts
3) At the 12 o'clock (centre) position, the wiper is 2.5v
4) At the 3 0'clock position, the wiper is approx 4.9v
0v to 2.5v over 0-90 degrees is "linear" and 2.5v over 90-180 degrees is "linear", but certainly isn't enough data to determine the linearity of the pot.

Make a graph and give this thing some granularity! :D

PS. Or order some "real" components that aren't being sold because they didn't meet manufacturing tolerances. :D
 

hippy

Senior Member
as Tom suggested in #15, the "metal" layer appears to continue as far underneath the carbon track as it extends beyond the track to the "pins".
Zooming-in on the "1" wafer; it does look like the entire 'carbon track' is laid upon a metal hoop which has two splits at 3 o'clock and 9 o'clock so it's not a dead short between the outer pins.

It could be that the 'carbon track' is laid on an insulating layer at the top but not at the pin ends. That could explain the 180-degree result.
 

hippy

Senior Member
Thought - Maybe it is designed to be a 180-degree pot, intended to be used with a knob and spigot which limits rotation to 180 degrees ?

The makes sense; manufacturers using the same body and assembly process, just with different length pin to track solid metals underneath to set the rotation resistance across the travel distance, still being 270-degree rotation until the appropriate knob is fitted.
 

OLDmarty

Senior Member
Thanks all, i think the best (efficient) thing for me to do is simply try some alternate pots by other manufacturers.

I actually thought i was buying real alps/alpha pots via ebay, until they arrived with no brand on them, now they seem to be biting me in the bum with all my time-wasting and not focussing on the application itself (it happens).

Looking back at the earlier posts, i'm certain i used simple tin-cased pots (about 2 years ago) on my Analogue inputs and the lookup table (or select case) seemed to work across the whole pot range quite nicely.

Sadly, my recent need to use a pot-box test jig has opened some cans of worms. My latest arrival of metal body pots had 3 failures out of 8, then i moved onto the green pots as the alternate solution.
It just seems to be 1 headache following the next...Grrrr.

I'll keep in mind to order REAL alps/alpha pots, or decent tin-can pots from a reliable outlet like Element14, Mouser, digikey or wherever else.
 

AllyCat

Senior Member
Hi,

It would be nice to resolve what the real issue is. Do they actually measure about 10k across their outer pins (give or take 1k or so)? If they do, then presumably they were intended to be "180 degrees" pots as hippy proposed. If they measure a few kohms low, then perhaps somebody "forgot" to put an insulating layer under the track, near its ends. Any other resistance value and I think we can assume that they are just "factory rejects" as suggested by tE/Tex.

Cheers, Alan.
 

OLDmarty

Senior Member
Hi,

It would be nice to resolve what the real issue is. Do they actually measure about 10k across their outer pins (give or take 1k or so)? If they do, then presumably they were intended to be "180 degrees" pots as hippy proposed. If they measure a few kohms low, then perhaps somebody "forgot" to put an insulating layer under the track, near its ends. Any other resistance value and I think we can assume that they are just "factory rejects" as suggested by tE/Tex.

Cheers, Alan.
Yeh, i'll do some measurements when i'm back at the bench tomorrow, but after tomorrow i'll consider them rejects and move forward ;-)
 

OLDmarty

Senior Member
OK, frustrating....

The carbon track measures around 20-50ohms at its end, with respect to the bare metal end tab.
The resistance continues to increase as i measure along the carbon track, and ending as 10k from end-to-end of the carbon track.

It's 5k in the middle (12 oclock) of the carbon track and approx 500ohm & 9k at the 3 & 9 oclock positions of the track.

So, it seems it's not limited to a 180 degree range of resistance. It 'seems' to be a normal pot ;-(

Anyway, i'll be moving onto other pots later through the week and move forward with my project.
 

premelec

Senior Member
I've seen many 270 deg and some 360 deg and 3 to 15 times 360 deg pots [multi turn] but don't recall seeing any 180 deg - would be useful for a 180 deg servo feedback... [also have seen tapped pots at mid point or other points]. Something new... ;-0
 

AllyCat

Senior Member
Hi,
Thanks for the update.
The carbon track measures around 20-50ohms at its end, with respect to the bare metal end tab. ....
approx 500ohm & 9k at the 3 & 9 oclock positions of the track.
So the resistance across the thickness of the carbon track is about 20-50 ohms, which seems quite reasonable.
The "Active operational angle" is about (1.5 + 8.5) / 8.5 * 180 = 210 degrees which is certainly lower than the "normal" angle of 270 - 300 degrees. It probably will have to remain a mystery whether they were manufactured as a "mistake" or designed for a specific, unusual application*.

But I don't think there is any "absolute" specification, and of course there are also "straight track" and/or multi-turn pots, and 360 degrees versions for "Wind Vanes" and similar applications. Also, in most cases, the ends of the pots may have some physical "Dead space" and/or a Minimum "terminal" resistance. Perhaps even some "Wiper" resistance - I don't know how those Wind Vane pots avoid shorting out the power supply at 360 degrees!

It's one of the hazards of eBay purchases (particularly if low priced) and a reason why we on this forum so often say "Please point us to a Data/Specification Sheet". ;)

*OT: Many, many years ago, the company I worked for had to sell a batch of "Teleprinters" (electric typewriters) at a ridiculously low price because somebody had specified that they should have an "ABCDEF" keyboard (not QWERTY) which made them absolutely useless for any professional "touch" typist. :)

Cheers, Alan.
 

OLDmarty

Senior Member
Hi,
Thanks for the update.

So the resistance across the thickness of the carbon track is about 20-50 ohms, which seems quite reasonable.
The "Active operational angle" is about (1.5 + 8.5) / 8.5 * 180 = 210 degrees which is certainly lower than the "normal" angle of 270 - 300 degrees. It probably will have to remain a mystery whether they were manufactured as a "mistake" or designed for a specific, unusual application*.

But I don't think there is any "absolute" specification, and of course there are also "straight track" and/or multi-turn pots, and 360 degrees versions for "Wind Vanes" and similar applications. Also, in most cases, the ends of the pots may have some physical "Dead space" and/or a Minimum "terminal" resistance. Perhaps even some "Wiper" resistance - I don't know how those Wind Vane pots avoid shorting out the power supply at 360 degrees!

It's one of the hazards of eBay purchases (particularly if low priced) and a reason why we on this forum so often say "Please point us to a Data/Specification Sheet". ;)

*OT: Many, many years ago, the company I worked for had to sell a batch of "Teleprinters" (electric typewriters) at a ridiculously low price because somebody had specified that they should have an "ABCDEF" keyboard (not QWERTY) which made them absolutely useless for any professional "touch" typist. :)

Cheers, Alan.
Hi Alan,
I hear you loud & clear "buyer beware", or, "stop buying crap" hahaha.

Hmmm, i bet those "ABCDEF" teleprinters are now worth something in the collectible/technology communities.
I still own some old Siemans Model 100 teletype machines, they're fun in their own vintage way ;-)
 

hippy

Senior Member
So, it seems it's not limited to a 180 degree range of resistance. It 'seems' to be a normal pot ;-(
Except that doesn't match with the ADC readings given as the pot is turned through 270 degrees. But I am at a loss to explain the discrepancy.

I would suggest connecting a 270 degree pot and if that works as expected, showing linear change during the first and last 45 degrees, then I think it has to be concluded that the original pot is designed for 180 degree operation, rotation limited by knob design.

I have never used a 180 degree pot but they do seem to be a thing. I would have expected them to only have 180 degree travel, not 270, but I guess that's not a problem for those who do use them and would be aware the desired result is achieved by a knob which limits rotation to the desired 180 degrees,

Coming at it when expecting that makes sense. It's just not so obvious that's how it is when coming at it with only 270 degree experience.
 

rq3

Senior Member
Hi again,

OK, Here's some pot voltage measurements...

The voltage at the pot-ends are 0v and 5.178 volts (stable).

Interesting to note, that at the pot-ends, it only takes about 2mm of movement from either end stop to begin a change in wiper voltage readings as compared to the code where it appears to be 10mm of travel before a change occurs from either end-stop.

ALL 8x pots measure as follows...
1) At the 0v end, 2mm travel from the end-stop changes from 0v to 10 millivolts and scales upward with wiper travel.
2) At the 9 0'clock position, the wiper is approx 180 millivolts
3) At the 12 o'clock (centre) position, the wiper is 2.5v to 2.6v (+/- 100 millivolts), based roughly on my knob being fitted exactly central (or not).
4) At the 3 0'clock position, the wiper is approx 4.9v
5) At the 5v (5.178v) end, 2mm travel from the end-stop changes from 5.178v to 5.168 volts and scales downward with wiper travel.

FYI: ALL voltages above are identical when measured on the picaxe pins too.
(there is approx 1 metre of ribbon cable between pot-box test jig and the picaxe board, but no voltage losses).


The pots being measured are the pots in my actual "pot-box" test jig.
When this jig is plugged into my 40X2, it seems the LEDS don't start changing patterns until the wiper is moved approx 10mm from either pot end, and as i said earlier, it's only the central 180 degrees of pot movement that seems to cause the LEDs to change with each 1mm movement.
(i was hoping the segmenting of my lookup table (or select case) would evenly distribute the LED patterns across the entire pot range).
Well, this dredges up a memory from at least 50 years ago. Pots from an analog computer which had logarithmic response for the first and last 10 or 20 degrees of travel, and linear response in between. Or maybe it was the other way round. Why they were designed that way, I can't say. They also had a 10:1 reduction, gear driven vernier knob, so they could be set repeatably. Just a "for what it's worth" note.
 

premelec

Senior Member
One of my favorite pot hybrids that sort of implemented vernier was two pots on same shaft one 10 times R of the other and mechanical 'slop' between the major change and minor change pot so when you backed off from slight overshoot of the setting changing direction of rotation only actuated the minor change pot for 10 degrees or so... then picked up the major change again...
 
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