big arduino volume knob

10 Feb 2024

A few months ago I bought a used MOTU UltraLite mk3 Hybrid, the oldest model of this interface that still works with Apple Silicon. It has 2 preamp inputs, 6 analog inputs, 8 analog outputs, 24-bit 192 kHz sampling. Very cool for very cheap. It has a lot of DSP bells and whistles that I probably won’t use, but I wanted something I with a few inputs for mics/synths, and could maybe send audio from Max or Ableton to a few cheap speakers/amplifiers for performances.

The monitor level knob on the front is fairly small and it sits in the corner of my office, where it isn’t particularly easy to reach while working. MOTU’s software CueMix FX allows control over USB of a zillion mix parameters including EQ, reverb, send/return loops, and (fortunately for me) monitor level, but the monitor level knob in the GUI is also small.

I found a 2014 blog post by Yan Pujante1 explaining how to control monitor level in CueMix using MIDI/OSC. His solution uses osculator, a paid application for routing MIDI and OSC messages between other software and hardware. I’m relatively frugal, so I wanted to create my own solution instead of buying another piece of software.

I built a first draft of a Max patch using MIDI CC from a 16n faderbank to control volume. It worked well enough, but I wanted to have a self-contained single knob/slider to control monitor level. I decided to try putting together a little Arduino project with an encoder. I found another post with code I could use for my purposes. The encoder increments/decrements an integer counter in the arduino, which it sends over serial. Max converts that to a float between 0 and 1, and sends that to CueMix over OSC. The push button on the encoder mutes audio until you turn the knob again. It would be nice to handle all the OSC in the Arduino code without some Max middleware, but I couldn’t figure it out this afternoon so this solution will work for now.

Parts were about $30 and an osculator license is $24. So much for being frugal.

----------begin_max5_patcher----------
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-----------end_max5_patcher-----------
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#define SW 2
#define DT 3
#define CLK 4

int counter = 0;
int counterIncrement = 5;
int currentStateCLK;
int lastStateCLK;
unsigned long lastButtonPress = 0;

void setup() {
    pinMode(CLK, INPUT);
    pinMode(DT, INPUT);
    pinMode(SW, INPUT_PULLUP);
    Serial.begin(9600);
    lastStateCLK = digitalRead(CLK);
}

void loop() {   
    currentStateCLK = digitalRead(CLK);
    
    if (currentStateCLK != lastStateCLK  && currentStateCLK == 1){
        if (digitalRead(DT) != currentStateCLK) {
            counter += counterIncrement;
        } else {
            counter -= counterIncrement;
        }
        counter = constrain(counter, 0, 127);
        Serial.write(counter);
    }

    lastStateCLK = currentStateCLK;

    int btnState = digitalRead(SW);
    if (btnState == LOW) {
        if (millis() - lastButtonPress > 50) {
            Serial.write(255);
        }
        lastButtonPress = millis();
    }
    delay(1);
}

Footnotes

  1. Apparently a cofounder of LinkedIn. ↩