Potentiometer Row Mounting/Ideas

[jonnojonno]

Hello all,

I'm pretty new to all of this, so let me know if this is not the place to ask these sort of questions.

The Background:
I think I've been a little overambitious with my first electronics project, an Arduino-driven MIDI sequencer. Roughly, there are 8 steps to the sequencer, with 4 properties that can be controlled per step, all controlled via potentiometers, for a total of 36 pots mounted. With my first iteration of this project, I thought I could get by with directly soldering wires to the leads on the pots, and through a combination of tight tolerances, and lack of strain relief, a good portion of my pots are not operating as I was hoping, necessitating painful replacement of individual pots with broken pins. It's at this point that I concede that this was the wrong way to go about things, only I'm still in the dark as to the better/best way of doing things is.


The Questions -- Answers to any of them would be most helpful!
Is there a far better way to mount these pots to say, perfboard?
The "PCB mount" pots that I bought have little tabs that seem incompatible with perfboard, is there a different board format I should look for?
Does anyone else have an example of how they did knobs at this scale a little neater than I have?
Or perhaps, even better... are there any PCBs made for this exact use-case?
If there aren't, could anyone recommend where I can look for odd-sized perf/stripboard that's long and thin, say 1x8 inches?

 

[JimB]

The "PCB mount" pots that I bought have little tabs that seem incompatible with perfboard,

Not all PCB mount pots are created equal, it would be helpful if you have a link to the pots which you bought.
Then we will be able to advise.

Welcome to ETO.

JimB

 

[Pommie]

Your original approach should have worked but if you pull the wires hard enough that you snap pins then that's the problem. Mounting on PCB or stripboard will only move the problem to where the wires join the board.

Mike.

 

[jonnojonno]

Thanks guys for your quick replies!

Not all PCB mount pots are created equal, it would be helpful if you have a link to the pots which you bought.
Then we will be able to advise.

I don't have a link handy, but I can give you a picture to illustrate what they look like. Perhaps there's a different type that better suits my needs?

Your original approach should have worked but if you pull the wires hard enough that you snap pins then that's the problem. Mounting on PCB or stripboard will only move the problem to where the wires join the board.

It indeed did work, at least for 30 of the 36 pots! However, now upon actual mounting and testing, six of them that were tested prior to use are now not working once mounted and soldered in. I'm now in the situation where to replace them, I'm likely going to have to desolder a good portion of what I've already done, and I feel that that amount of motion will only cascade more issues as I move those wires around. It's at this point I'm at a crossroads of continuing to make what I've done work, or consult more seasoned people as to how they would have done it to begin with.


There is method to that rat's nest, but the more I look at it, the more I wonder if there's a better way to integrate all of that wiring onto a rigid circuitboard; something that would consolidate the actual leads (+3v, ground, 8x data) per row to a single place with screw terminals securing them.

I google for a readymade solution and what comes up looks like this:
Link to an Etsy page for Pot Mounting PCB

This looks very closely like what I'm envisioning, however I'm wondering if there's a whole class of products just like this, if I only know the term to search for, and/or perhaps a vendor?

 

[Visitor]

Laying out your own printed circuit board for this project. A custom designed 100mm × 100mm pcb can be on your doorstep for about $25 total, for 5 or 10 copies. A larger board would cost a little more.

I don't know what you're doing with the pot signals; a board might hold just the pots and some part of your circuit or your entire circuit.

EasyEDA software from JLCPCB is actually pretty easy to learn and use and is free. Laying out the board will take a little effort, but probably not as much as hand-wiring pots to a perf board, and the result will be a rugged board that looks great.


For knows, check out Taya Electronics. They have many styles of knobs in many colors – be sure to pick knobs that fit the shafts on the pots you're using.

 

[jonnojonno]

Laying out your own printed circuit board for this project. A custom designed 100mm × 100mm pcb can be on your doorstep for about $25 total, for 5 or 10 copies. A larger board would cost a little more.

I don't know what you're doing with the pot signals; a board might hold just the pots and some part of your circuit or your entire circuit.

That might just be the direction I should go in! I was hoping my use-case was common enough that there would be a nice off-the-shelf pcb for me, but I'm not adverse to learning how to do custom PCB.

My circuit is split across a few boards in a cigar box enclosure, with arduino, and daughterboards with multiplexers at the bottom, and inputs mounted in the lid. The combination of the rigidity of the wires, the open-close motion of the box, and the frailty of the pins on the pots was a recipe for disaster that I should have seen coming, honestly. I'd be very happy just to create a pcb with common +/- buses, and a place for a header/screw terminal, with the traces leading to the wiper pins of the pots.

 

[Pommie]

EasyEDA software from JLCPCB is actually pretty easy to learn and use and is free.

Seconded.

How are you going to read 36 pots into the Arduino? Even the Mega only has 16 analogue inputs. I'm assuming that the 36 pots simply output a voltage between 0 and 5V - is this correct?

Mike.
Edit, what is the spacing between pots?
Edit2, I see your reply above and assume the multiplexers are to increase the I/O.

 

[jonnojonno]

How are you going to read 36 pots into the Arduino? Even the Mega only has 16 analogue inputs. I'm assuming that the 36 pots simply output a voltage between 0 and 5V - is this correct?

Edit, what is the spacing between pots?
Edit2, I see your reply above and assume the multiplexers are to increase the I/O.

Yes, if I recall, I'm supplying +3.3v to all my pots, anything supplied back should be below that. I'm using three muxes, two to read the 32 analog channels coming from the pots, and one to drive digital output to LEDs indicating which step the sequence is currently on. The additional 4 pots are for general properties like tempo, and are fed into the native arduino pins without muxing.

Spacing between pots is roughly 0.8 inches (entire pot matrix is 6.5 inches wide w 8 pots) , however, I'll likely scrap this enclosure altogether, so a new board may follow different dimensions.

All in all, Everything seems to work within the code, and the pots that are working, but there's this growing constellation of dead pots that really detract from me enjoying this thing!

 

[alec_t]

the rigidity of the wires

Sounds like the wire could be a lot thinner. It's carrying very little current. Thin solid conductor, or stranded wire, would place negligible strain on the pot pins.

 

[JimB]

I agree with alec_t, the wires are single core, a better choice would be stranded wire.

I would be inclined to use 7/0.2mm wire, (seven strands of 0.2mm diameter wire).

I used that sort of wire on this project:

JimB

 

[Nigel Goodwin]

I agree with alec_t, the wires are single core, a better choice would be stranded wire.

I would be inclined to use 7/0.2mm wire, (seven strands of 0.2mm diameter wire).

I used that sort of wire on this project:

I agree, he used a very unsuitable wire for his pots, and a very messy way of connecting them.

Yours looks lovely on the top, but what about the bottom?

There also seems a rather minimum of wire colours used?, presumably you wired it one wire at a time?.

 

[gophert]

These ribbon connectors take all of the tedious actions out of installing something like 32 pots. It turns the task of soldering wire ends into a plug/play process. Soldering a 25-pin connector to a board is so much easier than soldering 25 wires to a connector. Also, crimping pins on a connector is a pain in the butt.
Watch this and you'll never use another method for low current signals for pots/sensors.

 

[JimB]

A bit of thread drift coming up here...

Yours looks lovely on the top, but what about the bottom?

You asked, so here it is:

Not all of those 96 wires from the DIN41612 connector are used, but I decided that it was better to just wire them all, just in case.
A later modification would be a real pain.

There also seems a rather minimum of wire colours used?, presumably you wired it one wire at a time?.

Yes.
I cut the wires to length in batches of 32 ( 32 red, 32 blue, 32 black), soldered them to the connector and then formed the cable harness.
I then used a multimeter to select the correct wire to connect to the Vero pin on the circuit board.

JimB

 

[Nigel Goodwin]

A bit of thread drift coming up here...


You asked, so here it is:
View attachment 127254

Not all of those 96 wires from the DIN41612 connector are used, but I decided that it was better to just wire them all, just in case.
A later modification would be a real pain.

Actualy it's pretty neat - but I expected far more wires

 

[jonnojonno]

I agree, he used a very unsuitable wire for his pots, and a very messy way of connecting them.

I agree, and it definitely is evident this is my first project. My design choices were driven by what I had available versus what was actually needed. I only hope to improve by making fewer of the same mistakes in the future.
The burned hand teaches best, and hopefully I get a sizeable education from these issues I've made for myself.

These ribbon connectors take all of the tedious actions out of installing something like 32 pots. It turns the task of soldering wire ends into a plug/play process. Soldering a 25-pin connector to a board is so much easier than soldering 25 wires to a connector. Also, crimping pins on a connector is a pain in the butt.
Watch this and you'll never use another method for low current signals for pots/sensors.

I was really wondering how people did those sort of connectors, and really glad to see that it's simpler than I thought. I was expecting a specialized crimping tool, and I will definitely look toward using them with my consolidated PCB version to come.

 

[gophert]

Also, what value are all of the pots? I have a case of 10k slider/fader pots (4-inch) if that is interesting. Some failed project but they are still in the original trays. I think I have about 60+ parts. Let me know.

 

[KeepItSimpleStupid]

Evert hought about using encoders and A/D converters?

 

[jonnojonno]

I'm very surprised at how intuitive the whole process seems so far. Given the fact that I'm ordering a batch of these, I figured I'd add an optional strip of status LEDs.

I think all I lack is to add some additional silkscreen labels, and perhaps some optional mounting holes. I submit my initial work to the experts for pointers, in case I've drawn my traces too close together, or some similar beginner faux-pas of pcb design.

Also, what value are all of the pots? I have a case of 10k slider/fader pots (4-inch) if that is interesting. Some failed project but they are still in the original trays. I think I have about 60+ parts. Let me know.

That's super generous of you! I think I had better work from my own supplies, I'll feel less guilty ruining my parts than yours!

Evert hought about using encoders and A/D converters?

I'm not sure if I fully understand my options with those sort of circuits and logic-- I am using a singular rotary encoder+button for menu navigation and modification of runtime properties, so I have a little familiarity, however, figuring out how to debounce that guy was a challenge I won't readily forget.

Are you suggesting similar for the rest of my pots? That each change would fire an event (increment/decrement) that would take the place of analogReads?

 

[KeepItSimpleStupid]

Two things:

1. Your PCB. Use a copper pour, that would reduce waste and it might make the boards cheaper.
2. You really failed to tell us what your using the POTS for, but I'm assuming creating voltages.

I haven't seen this sort of digital pot before. ie. https://www.analog.com/media/en/technical-documentation/data-sheets/AD5291_5292.pdf
Take a look at this article: **broken link removed**
Here https://www.analog.com/media/en/technical-documentation/data-sheets/AD5220.pdf is the AD5220 datasheet.

There is some trickiness in using them. With the EDN article, all of the pots would reset when you removed power which may not be good for you.

You might have to hunt around for something that would work for you. Don't know if you can find something with the up/dn and clock input and with the ability to read position via I2C. Let's say something like that exists and 128 steps is OK. Then there is the issue of the position of the pot means something.

So, let a push on the encoder set the value in FRAM memory. This would keep the value after a power down without the need for battery backup.

I don't know what might work for you.

 

[jonnojonno]

The Copper pour: Thank you, this is exactly the sort of info I know I'm lacking.

Regarding the nature of pots: I suppose I have failed to mention how I'm using the pots, because I guess I only know pots to have the one use I've been using them for: basically, a dimmer--- a variable resistor that sends an arbitrary voltage down a wiper pin that's somewhere between full supplied voltage and 0, depending on ohm rating and linearity. My goal is pretty simple, provide a common rails for 3.3v and ground, and return 8 wipers worth of voltage back to an Arduino's analog pin. I'm guessing they have much fancier properties I've yet to understand.

Also thank you for the info on encoders, that looks pretty interesting! I'm not sure they fit my use-case with this project, but they really look neat. I may have to come up with a project that centers on them for my next outing into amateur electronics.

I confess that 90% of my electronics knowledge comes from a little 1000 in 1 Radio Shack kit I had when I was a kid 25 years ago, and I appreciate everybody's patient input with me. I've always wanted to try to build something myself, but never could come up with anything useful yet also suitable for a complete novice.