Analog Inputs (Knobs & Joysticks) Reference¶

The Gamma synthesizer exposes 8 analog user controls (4 potentiometers and 4 joystick axes) plus 1 auxiliary power/battery sensing channel, all multiplexed into the STM32H750's ADC1 converter.

1. ADC Channel Mapping Table¶

0-Indexed	1-Indexed (Physical)	Name	Function	Daisy Seed Pin	STM32 Pin	ADC1 Channel	Software Polarity
`0`	Knob 1	Chord Vol	`seed::D18`	`PA7`	`ADC1_INP7` (`A3`)	Inverted (`1.0 - raw`)
`1`	Knob 2	Chord Filter	`seed::D17`	`PB1`	`ADC1_INP5` (`A2`)	Inverted (`1.0 - raw`)
`2`	Knob 3	Notes Vol	`seed::D19`	`PA6`	`ADC1_INP3` (`A4`)	Inverted (`1.0 - raw`)
`3`	Knob 4	Notes Filter	`seed::D20`	`PC1`	`ADC1_INP11` (`A5`)	Inverted (`1.0 - raw`)
`4`	—	Left Stick X (LX)	Modulation / Pitch	`seed::D22`	`PA5`	`ADC1_INP19` (`A7`)	Normal (`raw`): Left=0%, Right=100%
`5`	—	Left Stick Y (LY)	Modulation / Pitch	`seed::D21`	`PC4`	`ADC1_INP4` (`A6`)	Inverted (`1.0 - raw`): Down=0%, Up=100%
`6`	—	Right Stick X (RX)	Filter / FX Control	`seed::D24`	`PA1`	`ADC1_INP17` (`A9`)	Inverted (`1.0 - raw`): Left=0%, Right=100%
`7`	—	Right Stick Y (RY)	Filter / FX Control	`seed::D23`	`PA4`	`ADC1_INP18` (`A8`)	Inverted (`1.0 - raw`): Down=0%, Up=100%
`8`	—	Auxiliary ADC	Battery / Rail Sense	`seed::D31`	`PC2`	`ADC1_INP12` (`A12`)	Direct voltage readout

2. Ergonomic Layout & Criss-Cross Playing Design¶

The physical placement of the 4 knobs across the top panel (Knobs 1 to 4 from left to right) is intentionally crossed relative to the keypads:

Left Keypad (Note Keys N1–N7): Played with the left hand. The corresponding Note controls (Knob 3: Note Vol, Knob 4: Note Filter) are located on the right side of the top panel, allowing the player's free right hand to tweak volume and filter cutoff simultaneously while holding notes.
Right Keypad (Chord Keys C1–C7): Played with the right hand. The corresponding Chord controls (Knob 1: Chord Vol, Knob 2: Chord Filter) are located on the left side of the top panel, allowing the player's free left hand to adjust chords without crossing wrists awkwardly over the playing hand.

3. Electrical Polarities & Inversion Details¶

4 Potentiometers (Knobs across top panel)¶

Physical Sweep: The potentiometer wipers sweep from 3.3V at fully counter-clockwise (CCW) to 0V at fully clockwise (CW).
Software Inversion: Must be inverted in software so that 0.0f = CCW and 1.0f = CW:

float val = 1.0f - hw.adc.GetFloat(channel);

2 Dual-Axis Joysticks (Thumbsticks)¶

Vertical Y-Axes (LY, RY): Both gimbals output 3.3V at bottom and 0V at top. Must be inverted:

float y_val = 1.0f - hw.adc.GetFloat(y_channel); // Down=0.0f, Up=1.0f

Horizontal X-Axes (LX, RX):
LX (Left Stick): Normal polarity (raw). Left = 0.0f, Right = 1.0f.
RX (Right Stick): Electrically inverted on the PCB layout to simplify ground plane continuity without via crossings. Must be inverted in software: 1.0f - raw so that Left = 0.0f, Right = 1.0f.

3. Initialization Code¶

All 9 channels are initialized using an array of daisy::AdcChannelConfig:

#include "daisy_seed.h"
#include "gamma_pins.h"

using namespace daisy;

constexpr size_t NUM_ADC_CHANNELS = gamma_pins::knobs::COUNT + 
                                    gamma_pins::joysticks::COUNT + 1; // 4 + 4 + 1 = 9

void InitAdc(DaisySeed& hw)
{
    AdcChannelConfig adc_cfg[NUM_ADC_CHANNELS];

    // Channels 0..3: Knobs
    for(size_t i = 0; i < gamma_pins::knobs::COUNT; i++)
    {
        adc_cfg[i].InitSingle(gamma_pins::knobs::pins[i]);
    }

    // Channels 4..7: Joysticks (LX, LY, RX, RY)
    for(size_t i = 0; i < gamma_pins::joysticks::COUNT; i++)
    {
        adc_cfg[gamma_pins::knobs::COUNT + i].InitSingle(gamma_pins::joysticks::pins[i]);
    }

    // Channel 8: Auxiliary ADC
    adc_cfg[gamma_pins::knobs::COUNT + gamma_pins::joysticks::COUNT].InitSingle(gamma_pins::aux_adc::pin);

    hw.adc.Init(adc_cfg, NUM_ADC_CHANNELS);
    hw.adc.Start();
}

4. Jitter Filtering & Responsive Smoothing¶

Knobs (Heavy Smoothing / Deadband): Potentiometers set steady synthesizer parameters. Use a micro-jitter deadband (0.005f to 0.015f) or a heavy IIR low-pass filter (iir = 0.002f).
Joysticks (Fast Responsive Smoothing): Joysticks are expressive performance controls. Use a responsive IIR filter (iir = 0.05f) with center calibration (~0.50f).

static float g_knobs[gamma_pins::knobs::COUNT]       = {0.0f};
static float g_sticks[gamma_pins::joysticks::COUNT] = {0.5f, 0.5f, 0.5f, 0.5f};

void ReadAnalogControls(DaisySeed& hw)
{
    // 1. Read Knobs (0..3) with inversion & deadband
    for(size_t i = 0; i < gamma_pins::knobs::COUNT; i++)
    {
        float raw = hw.adc.GetFloat(i);
        if(gamma_pins::knobs::invert[i])
            raw = 1.0f - raw;

        raw = fmaxf(0.0f, fminf(1.0f, raw));

        if(fabsf(raw - g_knobs[i]) > 0.005f)
        {
            g_knobs[i] = raw;
        }
    }

    // 2. Read Joysticks (4..7) with polarity normalization & IIR filter
    for(size_t i = 0; i < gamma_pins::joysticks::COUNT; i++)
    {
        float raw = hw.adc.GetFloat(gamma_pins::knobs::COUNT + i);
        if(gamma_pins::joysticks::invert[i])
            raw = 1.0f - raw;

        raw = fmaxf(0.0f, fminf(1.0f, raw));

        // Exponential smoothing (alpha = 0.05)
        g_sticks[i] += gamma_pins::joysticks::iir_coefficient * (raw - g_sticks[i]);
    }
}

5. Joystick Center Deadbands for Bipolar / Dual-Function Controls¶

When mapping joystick axes to bipolar functions (such as pitch bend) or dual-mode split controls (such as a DJ master filter where pushing left engages a low-pass filter and pushing right engages a high-pass filter):

[!WARNING] Mechanical Resting Drift Hazard: Analog thumbstick return springs have a mechanical tolerance of \(\pm 0.04\) to \(\pm 0.07\) around the electrical center (\(0.50\)). Using a narrow deadband (e.g., \(0.45 - 0.55\)) will frequently cause an untouched joystick resting at \(0.56\) to engage the high-pass filter, completely cutting low-end bass and kick drums from the audio output.

Recommended Center Deadband (\(\pm 0.08\))¶

For center-bypassed split controls (like a master DJ filter on RIGHT_X), use a deadband of at least 0.42f to 0.58f:

float rx   = g_sticks[gamma_pins::joysticks::RIGHT_X];
int   mode = 0; // 0 = bypass, -1 = low-pass, +1 = high-pass
float target_cut;

if(rx < 0.42f)
{
    mode       = -1; // Low-pass mode
    target_cut = LogMap(rx / 0.42f, 120.0f, 16000.0f);
}
else if(rx > 0.58f)
{
    mode       = 1;  // High-pass mode
    target_cut = LogMap((rx - 0.58f) / 0.42f, 20.0f, 6000.0f);
}
else
{
    mode       = 0;  // Center deadzone: Filter bypassed
    target_cut = 1000.0f;
}