Another post about knobs

I decided to have a go at sourcing knobs again. This time I've tried to find factories or wholesellers, but it is damn hard. The problem it seems, is that I'm looking for the rarest element known to man - black knobs without a pointer and with D-shaft instead of knurled shaft.

I've been able to get in touch with a couple of vendors and one factory in the UK so far. 

Here is an overview:

Cliff Electronic Components Ltd

They produce and sell a large range of knobs, many of which are white labeled and sold by RS Components (RS Pro brand), Conrad and similar. 

Unfortunately, noone stocks pointerless knobs, much less D-shaft versions.

Example of what IS available

https://www.conrad.de/de/p/cliff-fc7233-drehknopf-schwarz-x-h-30-mm-x-16-mm-1-st-704510.html

From Conrad

From RS

But one thing can be learned from this - There is a series named KMR from Cliff that looks good - slightly rounded compared to what I'm looking for, but that's fine if I could get all knobs from them.

https://www.cliffuk.co.uk/products/knobs/rotary.htm#kmr12

After contacting sales at Cliff I got this:

It looks like I need the US version of D-shaft for my encoders. 

There are two problems - I can't find a small (10mm in diameter) version of the pots, and the MOQ per type is 2000. The 15mm one would cost me GBP 0.526 / each, the 25mm GBP 1.332 / each and the 30mm GBP 0.963.

I could actually see myself buying the 15mm one, if it wasn't for the fact that it differs from my other pots.

PMDWay

PMDWay sells a 40mm knob that looks like the ones I want: https://pmdway.com/products/40x19mm-aluminium-knob

Again, it has a knurled shaft and is also too big. Cindy from PMDWay helped me search for alternatives but were unable to find anything. She suggested commissioning my own from a manufacturer, starting at https://www.globalsources.com/electronic-components

I DID find a knob on globalsources earlier, but the vendor is no longer on there:

https://www.globalsources.com/si/AS/Ningbo-Best/6008852396046/pdtl/aluminum-encoder-knob/1168713794.htm

Action Hardware

https://actionhardware.co.uk keeps popping up in my image searches, particularly two knobs:

Unfortunately,  both are unavailable. They are however willing to help me do custom orders. The MOQ is 1000 and approximate prices between GBP 0.65 and GBP 1.50 /pce.

Ian at Action hardware says they stock parts similar to what I'm looking for and suggests KM-2100 and KM-2600:

CHK is CHK Electronics Ltd, https://www.chk-electronics.com/home.php, but the knobs are sooo similar to the Cliff ones that I amost think they are the same or related. On the CHK site I found these:

This knob looks perfect, so does this, but there are no drawings to tell me the sizes. (KM-2100 is 14mm according to Ian, but KM-2500 remains a mystery)

Aliexpress

All the knobs I've found so far has been from Ali. Here is a list of what I've bought that looks good:

JU-HIVOR

https://www.aliexpress.com/item/32843175222.html

These are perfect - but unfortunately knurled shaft as always. I've bought 100 of these and they are my fallback solution if I can't find anything. 17mm in dia and 14 mm high. JU-HIVOR could not help me find anything.

DIKAVS

I was able to buy a nice knob here, but it is too low and now it's unavailable too.

These are the best large knobs I've found - I snagged four 32mm and one 30mm ones, the last one they had. Knurled shaft of course, and nothing has appeared since. DIKAVS never got back to me when I asked for help either.

Luyu Store

https://www.aliexpress.com/item/4001093464710.html

Luyu has some reeeally good looking knobs, 10.2 x 16mm. Unfortunately, they are for switches and have 3.2mm square holes. It is possible to drill an 8mm hole and 3D print a D-shaft insert which is my fallback solution for smaller pots. Luyu did not get back to me when I tried contacting them.

Best Partner Mall

https://www.aliexpress.com/item/32952829517.html

These look great, but are too big for me and has that damn knurled shaft of course. 

Best partner mall have a lot of great knobs and I've bought a few alternatives from them too:

https://www.aliexpress.com/item/4000900076410.html

These are super nice! A bit costly but solid aluminum. If they had the same knobs in other sizes these would be my choice, even if they are quite expensive.

https://www.aliexpress.com/item/32921539254.html

Massive aluminum knobs with D-shaft. I consider using these for the main rotary encoder but it depends on what I find for the other knobs. Update: I actually bought mine from Warm Textile Home, see below

These are round shaft but that's ok for single pots. I liked that they did not look as much guitar knob.

Warm Textile Home

https://www.aliexpress.com/item/32802055908.html

This is the same knob as from Best Partner Mail and the one I actually bought.

CW Switches Electric Store

https://www.aliexpress.com/item/1005002809107285.html

This one is a bit of a mystery to me. I think it is the same knob as Best Partner Mail but I can't see that I've ordered from them.

Anyway, They have been super helpfull in finding alternatives. They say they can get me the one in the lower right corner with D-shaft. The MOQ is 500 and price $0.89 which is ok.

The same for 30 x 17, MOQ 500 and $1.68:

Then they suggested 15 x 17 D-axis:

This is a perfect one. I will ask for price and MOQ, and if it is within reach I will most likely buy it. 

I have also inquired about 10 x 16, 17 x 17 and 25 x 17, but that's where the dialogue stopped.

Shenzen Hengda Electronics

While not black, this is an honorable mention: A 24mm alu knob that may be a good alternative for the waveshaper/filter knobs. I have 10 of them.

https://www.aliexpress.com/item/1005003184444519.html

https://www.aliexpress.com/item/4001039507025.html

I reached out to Shenzen and they asked me for pics and details about what I need, but so far they haven't gotten back to me again.

Changshenghong

https://www.aliexpress.com/item/32873353173.html

Changshenghong has two sizes of pots that will go nicely with the ones above, though the 34mm one is a bit tall. Also, they are hideously expensive so I haven't bought any. I have not yet contacted Changshenghong ab out other variations.

HIFIw / HIFIvv / Hifi amplifier spare parts center

While not the same as the other knobs, they have some good looking knobs that MAY go well with my other guitar-ish knob:

https://www.aliexpress.com/item/32620216429.html

I've ordered a couple of these, possibly for the waveshape/filter knobs

SENGTERBELLE HIFI Audio World

https://www.aliexpress.com/item/32819963066.html

These look like smaller versions of the one above. They may be too small for me but I wanted to check them out anyway.

Other producers

Mentor

https://www.mentor.de.com/bauelemente/en/portfolio-2/portfolio-knobs/

Mentor have a few series of good looking knobs. Some are available at Elfa and other vendors, even without pointer: 

https://www.elfadistrelec.no/en/rotary-knob-without-line-aluminium-o30mm-mentor-513-61/p/11077374

https://www.elfadistrelec.no/en/rotary-knob-aluminium-o24mm-without-indication-line-mentor-508-61/p/11077363?trackQuery=&pos=25&origPos=25&origPageSize=50

They seem to be set-screw/round shaft versions.

DuPPa

Not sure how I stumbled upon this, but I found and ordered some cool variations of the guitar knob, this one fits an encoder with transparent shaft and RGB led:

https://www.duppa.net/shop/aluminum-black-knob-with-ring/

I hoped these would look better in real life but they are, especially the gray ones, a bit scruffy. Not TOO bad though. Since the center cap is black I think I would go with the all black ones, so lets see how it compares to the other black guitar-knob-ish ones I have coming.

I did however try the gray one on a black background, and the result is pretty good, better than expected. The pics do not do it justice though

DIY

I posted a question about knobs on the Synth DIY list on facebook, and a friendly soul pointed out that I could have them CNC milled. He payed around 3 euros for the small ones, 4.5 for the middle and 5.5 for the big (in Sweden):

Final notes

Here's a quick comparison of some of the knobs

They all go fairly well with the black knobs. As long as there is some distance between the matte black ones and the guitar-ish ones they go together very well. I still lean towards the grey sandblasted one for waveshape etc as it is exactly the same as the black ones. We'll see.

I did another test on the 17x14mm black caps to see if I could get a tighter fit on a 6mm D-shaft (I have tried drilling a 6mm hole earlier and it slides on but there is no friction. This time I drilled one with a 5.7mm and one with 5.9mm drill bits. The 5.7mm does not work. The 5.9mm can be pressed on but it's too tight and I broke the cap when trying to pull it off. I think my conclusion has to be that it's not viable, which means that I either have to drill a larger hole (8mm) and add an insert, or just have a D-shaped insert, but in that case the small D-shape must create all the friction and I don't think it will work very well. All in all, If I can use the 15x17mm instead, I think that's the better option.

PS: Here is my post about custom D-shaft insert for the 10mm pot: https://atosynth.blogspot.com/2021/03/from-33mm-square-to-d-shaft.html

PPS: There are various inserts available but hard to find something usefull. Search for knob spring, d-shaft inserts, barrel spring, d-shaft knob adapter

https://forums.qrz.com/index.php?threads/retainer-d-shaped-and-flat-springs-for-radio-knobs.643669/

https://www.allelectronics.com/item/spr-14/metal-insert-for-1/4-half-moon-shaft/1.html

Another idea: Buy something like these and cut of the top: https://sharvielectronics.com/product/potentiometer-knob-3mm-d-shaft/

UPDATE:

I tried spraying the 3D-printed insert with rubber spray and it works great! The knob sits firm but is still possible to remove. I will leave it on for some days and then try removing it again.

The grip was actually so good that it pulled the insert out of the cap (it had not been glued). This also showed that the rubber spray leaked through the 3D print. After letting it dry i put the cap back on and now it sits firmly again. 

I also tried spraying the outside of another cap. It adds a good grip but also removes the nice aluminum finish, and as far as I know it's not particularly durable, so I don't think I'll do it. It's nice to fall back to though, should the pots be too slippery. I did a black spray and was not very light handed so the finish was not the best, but I am sure it can be improved. I could also try transparent spray but that was sold out.

LED ring update

 I got some work done on testing the LED ring with the MAX7221 7 segment encoder today, and the results are great. Both single led and multi led indicators are feasible and each has its own use. 

I tried with various lenses but my current conclusion is that no diffuser, red lense and a black panel definitely looks the best. Using a diffuser only made it look muddy.

The MAX7221 greatly simplifies the design/code. Multiple ICs can be chained, and I also think multiple parallel devices on the SPI bus are possible. One IC covers two pots with 32 leds.

I also got some amazingly good looking knobs today, matt aluminum, no indicator. Unfortunately, they have knurled, not D shaft, so it may be hard to find an endless potentiometer to fit it.

UI/front panel design - living post

Here I'll post stuff about the UI that comes up during my research.

Endless potentiometers:

Also known as 360 degree pots - carbon potentiometers without an end stop. Alpha has one that has two carbon paths, making it possible to sense position and direction, and the paths have no jump in resistance at the end but rather increase then decrease. Can be used if we want more steps than an encoder can offer.

Lifetime for both pots and encoders from Alpha is 15000 turns.

One example is Alpha RV112FF

https://hackaday.io/project/171841-driveralgorithm-for-360-deg-endless-potentiometer
https://forum.arduino.cc/index.php?topic=531613.0


IDEA: For filter, use a "finger dial" like the data wheel on the Native Instruments KORE 2, with an option to do a fine grained sweep by pressing "shift" (this could really be an option for all pots, with a common shift somewhere).

Encoders: 

24 pulse/24 detent https://www.reichelt.com/de/en/alps-stec12e-rotary-pulse-encoder-24-24-vert-w-pb-stec12e08-p73923.html

Alternatives (like without detents):
https://tech.alpsalpine.com/prod/e/html/encoder/incremental/ec12e/ec12e_list.html

Each detent may give up to 4 increments when using a non-detent encoder. More info on this and on how to read multiple encoders using interrupts (and port expanders) here:

http://makeatronics.blogspot.com/2013/02/efficiently-reading-quadrature-with.html

https://www.eevblog.com/forum/beginners/rotary-encoder-pulses-and-detents-and-interrupts-vs-polling/

https://arduino.stackexchange.com/questions/52909/reading-several-rotary-encoders

LED ring:

Must decide if all or only one led is lit. Measure current used.

Can use a 7-segment display chip like the MAX7221


Light pipe solutions:
Laser cut a black ring with holes the size of the led. Put a diffused (engraved acrylic or milky white acrylic) and colored acrylic on top - will give clearly separated leds.

CNC a ring with holes, but slant the edges so they meet at the surface, will give minimum separation. May be a problem that viewing angle of the led does not spread the light enough.

Experiment with diffuser at top/bottom for increased spread

3D-print similar ring with slanted edges? Laser cut the bottom hole?

Make light pipes with separation, laser cut as a profile and mounted upright, will make it possible to have slanted edges in one dimmension,. with good internal reflection (?)

My initial tests of light pipes: https://atosynth.blogspot.com/2020/04/led-dial-light-pipes.html

A cool project with RGB ledring: https://muffwiggler.com/forum/viewtopic.php?t=217920

Knobs

White moog/boss style knobs:
https://lovemyswitches.com/knobs/?utm_source=share&utm_medium=ios_app
https://lovemyswitches.com/colored-boss-style-knob-knurled-shaft-11-x-20mm/
https://lovemyswitches.com/colored-boss-style-knob-1-4-smooth-shaft-11-x-20mm/
https://lovemyswitches.com/1360-tall-boy-knob-12-x-16mm/
Also has lots of other sizes but not white

Cheaper kn-13560 knobs: https://www.aliexpress.com/item/32430188458.html

https://www.conrad.com/p/alps-dk13-164a645-rotary-knob-for-encoder-with-plastic-shaft-rotary-button-700619

Switches

Cherry ML: https://cory.li/cherry-ml/

Nord Lead - switches: https://www.elektronauts.com/t/nord-replacement-switches-part-id-now-found/46469

https://www.elektronauts.com/t/nord-replacement-switches-part-id-now-found/46469/6

--> 6450 Marquardt

Cherry MX Low Profile

Other ideas:

Make the front panel detachable and use an RJ-45 to connect it to the synth, making it desktop friendly.

Morph functionality. Set A, set B (either patch or variation of patch). Big dial for morphing. Envelope based morph.

CNC'd mod wheels with acrylic inside?

Led indicator ring driver

I intend to have rings of LEDs around the potentiometers on my synth to show the current value of the parameter, and have been thinking about ways of doing it. One can take the normal approach and do a full matrix that runs through all the pots and have a single controlling circuit, but that requires a lot of data lines running across the PCB. Another option is to use a 16bit shift register per dial and connect each led to a pin, which reduces the number of lines necessary to six - two power lines, serial in-out and clock, latch.

I have been considering having even more LEDs per dial. For 32 LEDs this last method requires either two 16bit or one 32bit shift register, and things start being costly and take up a lot of board space.

Thus, a combination may be a good solution. If one uses a 12bit shift register, one can control 6 rows x 6 columns for a total of 36 diodes, while still only using 6 transmission lines (16 diodes may be controlled by a 4x4 matrix, requiring an 8 bit register only). It means you have to do row scanning instead of just updating the shift registers whenever the dials change, so there are pros and cons of each method. The scanning requires more (but cheaper) components - transistors and resistors. It also requires a more complex controlling algorithm which takes up time in the microcontroller, and ultimately the number of controllable LEDs and the refresh ratio is limited by the time it takes to fill the shift registers.

A possible circuit may look like this:

The shift register must be able to sink around 20mA per pin which means a normal CMOS chip won't do. A constant current sink led driver will be a good option, it may even do away with the resistors in the schematic.

I've found 16bit led driver shift registers at prices of just above $1in quantities of 50, for example the STP16CPC26 at mouser.com.

PS: a 32 LED dial may be controlled from a 12 bit shift register using 8 bits for rows and only 4 for columns. This reduces the necessary transistors from 6 to 4.