Archive for August 2009

Live at WORKS/San Jose, august 2009

Derek Scott demos beatseqr

awesome demo!

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prototype version 1 in action

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HOWTO find and buy faders / sliders / slide pots / slide potentiometers

Slide Potentiometers

While making my Beatseqr project, I’ve been trying to find a reliable source for some faders / sliders / slide pots / slide action potentiometers, and I’ve been having a challenging time finding exactly what I want. So I thought I’d share what I’ve learned. Click on through to get a crazy large dose of science.

Here are some of the parameters I’m working with:

  • I’m a hobbyist. I’m trying to make a project with a user interface, but I’m not trying (at this time) to make a hundred copies of my project. So I can’t order 1000 pieces of anything.
  • I can’t (won’t!) finalize on sending my PCB out until I have parts that I know I like, and that will work well for my project, and that I can go back and reorder if I do need to make more copies of my project.
  • Because I’m just getting started, I want to keep the total cost of parts as low as possible while maintaining the user experience I’m looking for.

Specific things i’ve learned:

  • You have to learn how to read datasheets. There’s just no getting around it if you’re thinking of making a repeatable project. If you don’t read the metric system, get ready to start doing that. And also get ready to start estimating or calculating how to go between imperial and metric, because not all manufacturers describe their parts one way, so when you’re comparing parts, you’ll see some talk about their parts in decimal inches, and others in millimeters.
  • Don’t always trust datasheets unless they’re drawn specifically by the manufacturer. I’ve ordered parts from a distributor (mouser!) only to discover that they weren’t at all like the datasheet provided by the distributor’s website. Notice the difference? The data sheet was provided by the distributor in an attempt to give more information about the slider, but they gave me the *wrong information*. Comforting, isn’t it?
  • There are only a handful of companies that make slide potentiometers — that are readily available in the USA — so consider learning who they are and how their part numbering systems work. Here are the usual suspects:
  • Also, don’t expect faders to be what these companies consider to be their sexiest products. They’re not. At best they’ll have some datasheets available for you to look at. At worst, you won’t be able to find sliders on their website… at all. It’s a little perplexing to me how companies can make stuff and not seem to even realize it as far as their website knows.

  • Linear movement potentiometers are not sliders/slide potentiometers/slide action potentiometers. Linear movement potentiometers appear to be made to track the movement of kinetic/robotic things in a factory. Probably used in conjunction with stepper or other kinds of motors or actuators. If you’re looking for a thing that goes on a user interface, these ain’t those.
  • Motorized faders sure look nice, don’t they? Crazy expensive!

There are several kinds of companies that will sell you parts, and they require different levels of commitment and experience.

  • Retail shops like Radio Shack (aka “The Shack”) or even Fry’s don’t even sell them at all. Probably because it’s so friggen’ complicated that there’s no mass market in it like there is with radial potentmeters.
  • Ebay – there may be some available, but the sheer number of parameters you should know before you buy anything makes this a really horrible idea unless the seller has taken great pains to make it clear what they’re selling. Most times you’ll see something like “slider for DJ mixer, $20″… totally inadequate information.
  • Hobbyist online shops or pro audio shops that sell music/speaker parts. These places will sell a few, but they’ll be extremely limited in their selection. They’ll at least tell you “slide potentiometer, 10k, $3 each” and list out some dimensions. Much better, but maybe still inadequate if you’re looking for repeatable purchases. (And/or may be overpriced if you need a quantity of 10 or more for your project)
  • Surplus stores (halted supply, electronics surplus) These places may well have what you need, may well be priced at or below (or sometimes extremely below) new retail prices. The only problem here is that they may not have what you need. Sometimes they’ll have frustratingly close to what you need, but not quite right. Or worse yet, they’ll have what you want today, and when you need more down the road, never again. Surplus stores are a mixed blessing. I wouldn’t trade my Halted Supply store for anything… except maybe a (fictitious) Mouser retail store. I’ve purchased some of the most important components of my life at a surplus store… some of the very components that ignited the fire of my understanding of how this world works, so if you have one of these places near you, don’t hesitate to look. They may have something from a manufacturer you’ve never heard of and it may provide a lead for your online searching.
  • General parts suppliers that have multiple hundreds of thousands of parts. (mouser, digikey) These places may have what you want, but you’ll need to understand how their websites work and how to search for what you’re looking for. This is closer to rocket science, but it’s doable. This is where I live now. They’ll show you a list of the parts they sell by you navigating to their “resistors” or “resistive products” section, then on to “potentiometers/rheostats”, and then if you’re lucky you can select “slide potentiometers” or search for “slide pot”. Alternately search for “slide” and then if they have any, they’ll list the number of parts under resistors.
  • Vertical market resellers/distributors. I’ll list out my experience of their websites below. If you’re a hobbyist, they’re probably not for you. They’re for large companies and the government/military. Sometimes you’ll see that they specialize in “milspec” parts or specific value-added manufacturing processes like cable-knitting or other services that are probably needed by large scale manufacturers. In most cases you’ll need to order multiple hundreds of your part in order for this to make sense. So far as I can tell, hobbyists like myself need not apply.
  • Manufacturers from overseas. Drool all you like at their nice components. Unless you need 10,000 pieces, it’s unlikely you’ll get to use what they make. I sorely wish someone would start a specialty components store for things like this: (potentiometer with led ring). Drool.

There are several parameters you should bre of before ordering a bunch of sliders. Here are the top ings to look for:

  • Mounting method. The most common ways are “PC mount”, where it’s soldered directly onto a circuit board, or “solder lug” where it’s intended to be mounted onto the control panel with screws and connected with wires. I’m guessing that the rule of thumb is that if you don’t see a “mounting holes diagram” on the datasheet, it’s not supposed to go to a circuit board. Some sliders also have additional curved or bent pins to help snap the slider into the circuit board. Make sure the datasheet is easy to read for what the hole pattern should be on your circuit board.
  • Recommended soldering technique. “Wave” soldering is not something you’ll be doing, so make sure they list out what temperature (ex: “manual soldering: 300° C for 3 seconds”) … some sliders I’ve seen datasheets for *don’t* recommend you manually solder them at all. Usually those are “open frame” sliders, but double check before you buy.
  • Control lever height. It *will totally matter* if you’re making a project with 1/4″ thick laser cut acrylic and the slider is mounted onto a circuit board. The tallest control levers I saw were 19mm tall… which is what (guesstimating using my newly activated metric to imperial translation skills), almost 3/4″ tall. If your slider isn’t tall enough, it may not give you much to grab onto once it’s poking over the control panel surface. There are a couple of other parameters here that may be important to you. How hard is it to move the lever, and how much “play” will the lever have if you push on it from the side? these are usually listed on the datheet, sometimes not.
  • Pins. Check the datasheet to make sure it explains how many pins there are and what pin does what. Which is the ground pin? which is the pin you measure the data value from? If I were you, I’d put a bit more trust in manufacturers that spend the time to document this in the datasheet. If the slider has an LED embedded in the lever, does the datasheet outline how to mount it on the PCB, and which pin does what?
  • Data curve. Be careful! If you’re doing a microprocessor-based project (PIC, Arduino, etc) you *probably* want a “Linear” curve (sometimes also known as “B” curve, sometimes called another letter). Linear curve pots, which are versus an “Audio curve” or “log curve” or “A curve” pot. This whole parameter will affect the rate in which the slider will read data values… this is definitely easier to show with a chart, so pardon my ham-handed guesstimate at the data points, and take a look here:
    curves
  • Center detent. Do you want that? A center detent is when the contol lever pops to a definite center point. This can be good in some instances, and bad in others.
  • Travel length. This denotes the actual amount of distance the lever will move. I’ve seen tiny 20mm to gigantic 100mm. 30mm, 45mm, and 60mm are common. This measurement usually refers to the distance the control lever travels, not the overall dimensions of the component itself. Make sure you don’t space your sliders too close together.
  • Knobs. I’ve not had great luck locating knobs specifically for sliders/faders. They’re out there, but without being able to test fit a range of contending knobs onto the specific fader you own, it’s hard to say whether a knob you see online will fit onto some random fader, even from the same website. Knobs can be really cheap, but if they don’t fit the parts you own… then they’re actually kind of expensive to order. :)

And lastly, and unfortunately, sometimes you need to just roll the dice and see what happens. Take your best guess, bite the bullet, order some parts and see what you get. Got any tips? Leave ‘em in the comments!


APPENDIX: United States suppliers of slide potentiometers


Companies that advertise in google adwords, or show up in top google search results for “slide potentiometers”:

mouser = 1600 products, datasheets have been proven to be wrong, but this really is the best resource I found for slide potentiometers.
tti = none / too hard to locate (mouser actually is tti)

digikey = 82 products, expensive, sometimes larger minimum purchase
newark = 74 products, expensive … same as
farnell/uk … 111 products, UK currency
tsan = none / large quantity sales only
allied = non-stocked, 100 minimum pieces for bourns (however, cheap)
arrow = 2 products, large quantity sales only
sager = 4 suppliers, large quantity sales only
future electronics = 1 product

And… here we go… here’s an exhaustive list of US suppliers as found on an electronics industry group’s website, and my comments. Where it says “none/too hard”, that means that they don’t deal with small-timers like me:

all american = large quantity sales only
all electronics = 1 product
avnet – non-stocked
bell industries / micro – none
bgmicro – none
capital – none
cdm – large quantity sales only
dr components – large quantity sales only
electronix express = none / easy
ericnet – large quantity sales only
fcc franklin choi = one
ibs = large quantity sales only
i systems = wtf?
icc = large quantity sales only
jaco = large quantity sales only
jdr = large quantity sales only
kentek = none
knight = large quantity sales only
tequipment / leader = none
lemos = none
mentor = large quantity sales only
mitronics = large quantity sales only
new york semi = large quantity sales only
NTI / connector people = none
north atlantic = large quantity sales only
nte = none
nuhorizons = none
powell = none
richardson electronics = none
richy cypress = arrow nac
space coast semi = large quantity sales only
4star elec = large quantity sales only