Table of contents

Potentiometers - knobs and faders

Potentiometers - knobs and faders

A potentiometer is a three-terminal resistor with a sliding or rotating contact that forms an adjustable voltage divider. If only two terminals are used, one end and the wiper, it acts as a variable resistor or rheostat.

It’s a knob or a slide fader that gives values between 0.0 and 1.0

Name

There are different types of potentiometers, but in this context we will focus on two common ones: single turn knobs and slide faders. They are both linear, which means that the output voltage changes proportionally to the position of the contact.

Single turn knobs

These are potentiometers that you can rotate (almost) 360 degrees. They look like dials or knobs that you can turn clockwise or counterclockwise.

They are linear, with a fixed range. And the knob types are therefore referred to as single turn - to differentiate clearly with the similar looking yet endless turning encoder.

Slide faders

These are potentiometers that you can slide up and down. They also have a fixed range. They look like sliders or levers that you can move along a track.

Technically they are the same.

So most commonly these would be the attributes you’re looking for in a potentiometer:

single turn, linear , 10k resistance.

For faders:

slide potentiometer, linear, 10k resistance

Function - what can it do

Potentiometers, or knobs and faders are a way to change values from one end to another.

While the potentiometer itself is read by the hardware in steps of 0 to 1023, it gets translated to/from a float value from 0 to 1.

Type	_variant	Behavior
Inputs	—	—
Voltage Input	—	Returns a floating point representation of the voltage at its input. The typical range is 0-5 V, which is represented as 0-1

In Plugdata you will be using 0 to 1 as the float values to control things. When needed you do simple maths, e.g. if you would need a value range of 0 to 127, you’d add a block [* 127].

(Comparable to the mapping function with Arduino’s.)

What it looks like

TODO: insert pictures/gif

Potentiometers

TODO: insert pictures/gif

Slider/fader

TODO: insert pictures/gif

Pins

These are analog components, by changing the position of the knob or fader you change the amount of voltage they allow to flow.

A potentiometer is a variable resistor with three pins. Two are connected to the ends of a fixed resistor. The middle pin is moving across this.

Hence, we need the analog pins on our boards. These are labeled as A0 to A11, these pins could be used for other things as well, so in the custom json we’ll have to instruct to use them as AnalogControl

Connect the outer pins to voltage and ground, connect the middle pin to an Analog pin.

Changing the order of the outer pins will change wether your knob/fader goes from 0 to 1 or reversed. When changing the wiring isn’t an option, or you might be holding your PCB in another orientation, upside down, at 90 degrees, you could reverse the values by sending it through these blocks: [* -1] - [* +1]

Follow this link to the spreadsheet showing the pin numbers used on/in the Daisy board, Plugdata, Synthux, …

Daisy seed pin numbers on the board	Daisy pin names digital	Daisy pin names analog	GPIO column middle	GPIO column outer L and R on the datasheet	Pin numbers on the Simple PCB microcontroller slot - corresponding to the row below the matrix	Pin names in synthux Analog and Digital simple-daisy.h	Pin names in synthux Mounted on the back AnalogOnTheBack and DigitalOnTheBack simple-daisy.h	Pin names in synthux simple-daisy-touch.h AND on the Touch PCB	Pin numbers for use in Plugdata custom json file
20	A GND	A GND	A GND	A GND	20			A GND
21	3V3 Analog	3V3 Analog	3V3 Analog	3V3 Analog	29			3V3 Analog
22	D15	A0	ADC 0		30	S30	S19	S30	15
23	D16	A1	ADC 1		31	S31	S18	S31	16
24	D17	A2	ADC 2		32	S32	S17	S32	17
25	D18	A3	ADC 3		33	S33	S16	S33	18
26	D19	A4	ADC 4		34	S34	S15	S34	19
27	D20	A5	ADC 5		35	S35	S14	S35	20
28	D21	A6	ADC 6		36	S36	S13	S36	21
29	D22	A7	DAC OUT 2	ADC 7	37	S37	S12	S37	22
30	D23	A8	DAC OUT 1	ADC 8	38	S38	S11		23
31	D24	A9	SAI2 MCLK	ADC 9	39	S39	S10		24
32	D25	A10	SAI2 SD B	ADC 10	40	S40	S09		25
35	D28	A11	SAI2 SCK	ADC 11	43	S43	S06		28
38	3V3 Digital	3V3 Digital	3V3 Digital	3V3 Digital	46			3V3 Digital
39	VIN	VIN	VIN	VIN	47			VIN
40	D GND	D GND	D GND	D GND	48			D GND

Components json

knob1 and faderleft in this example are the custom names you can choose, they are the names you’ll use in Plugdata.

    "components": {
        "knob1": {
            "component": "AnalogControl",
            "pin": 15
        },
        "faderleft": {
            "component": "AnalogControl",
            "pin": 16
        }
    }    

In plugdata we receive the values via a block with this text: r knob1 @hv_param

PD example(s)

As shown higher up, if you change the wiring direction of a potentiometer it’ll send inverted values. The examples below presume the direction is as you’d intent expect, if not, adding this small inverting trick solves it: [* -1] - [* +1]

inverting the value of a knob

Example - potentiometer controlling pitch and volume

In this example we connect knob1 to the frequency of an oscillator, and a fader controls the volume.

potentiometer fader analogcontrol Plugdata example

r knob1 @hv_param and r faderleft @hv_param receive knob and fader values (0 - 1) from the analog pins you setup in the custom json
hsl horizontal slider: note that while for smaller patches it’s not that important, but since this isn’t used in actual hardware, it’s good practice to keep it out of e.g. subpatches as it will take up some memory. Having many of these could add up.
$1 is a placeholder for the value received from the input, the second number will be taken by line as the time ramp in ms.
The line-object is a linear ramp, it receives the two numbers as follows:
- the first part $1, is the value that it will output;
- the second 20 is the time in milliseconds it takes to move to the next value, hence smoothing.

Smoothing and the signal~ domain

Smooth

At default setting you “read” the knob every 1ms, this could potentially introduce glitchy behavior if you send numbers every cycle, that’s why we want to smooth out any small fluctuations from turning your crappy dusty knob.

Making this time too long might make it feel lagging, but in some cases could be preferable to get even smoother / slower / gradual changes.

~Signal

Use line~, with the ~ to keep your patch as much as possible in this continuous signal domain.

Download this patch:

potentiometer_fader_analogcontrol.pd

Or copy this text and paste it in a Plugdata patch (it should get “transformed” into what you see in the screenshot above):

#X obj 282 119 r knob1 @hv_param;
#X msg 282 247 \$1 20;
#X obj 282 299 line~;
#X obj 282 352 *~ 440;
#X obj 282 405 osc~;
#X obj 379 503 dac~;
#X obj 387 466 *~;
#X msg 651 247 \$1 20;
#X obj 651 299 line~;
#X obj 651 119 r faderleft @hv_param;
#X text 431 465 mixing volume;
#X text 369 343 calculate / map to a new range \, this example maps val 0-1 to 0-440, f 34;
#X text 431 502 audio out Left / Right;
#X obj 306 185 hsl 102 21 0 1 0 0 empty empty empty -2 -8 0 10 #191919 #e1e1e1 #e1e1e1 0 1;
#X obj 691 185 hsl 102 21 0 1 0 0 empty empty empty -2 -8 0 10 #191919 #e1e1e1 #e1e1e1 0 1;
#X text 431 170 while testing in PD use a slider 0-1 \, delete when optimizing your patch, f 24;
#X text 431 103 receive knob value (0 - 1) from pin setup in custom json, f 24;
#X text 431 238 \$1 = knob value \, set 20ms as ramp time for ~line, f 24;
#X text 433 290 line~ for smoothness \, sig~ for continuous., f 24;
#X text 367 396 cosine wave oscillator \, the input is the hz, f 24;
#X connect 0 0 1 0 32.................s.........PK.........jE....;
#X connect 1 0 2 0 32.................E.........PA.........n.....;
#X connect 2 0 3 0 32.................O.........vC.........3A....;
#X connect 3 0 4 0 32.................P..........D.........7A....;
#X connect 4 0 6 0 32.................S....jF...vD....oA...jB....;
#X connect 6 0 5 0;
#X connect 6 0 5 1;
#X connect 7 0 8 0 32.................E.........PA.........n.....;
#X connect 8 0 6 1 32.................9A...Pv+++ue....D7+++6H....;
#X connect 9 0 7 0 32.................s.........PK.........jE....;
#X connect 13 0 1 0;
#X connect 14 0 7 0;

links / references / sources

buy potentiometers on Thonk

TODO:

link to synthux docs/vids