Shared potentiometer

The Arduino tells the browser "I have an analog input on A0 — start polling it." The browser does nothing more than listen. A turn of the knob shows up live on screen.

Arduino

shared-potentiometer.ino — the Arduino side

#include <Pardalote.h>

const int POT = A0; // e.g. A0 for UNO R4, GPIO 36 (ADC1) for ESP32

void setup() {
    Pardalote.begin();
    pinMode(POT, INPUT);

    // Tell the browser "A0 is an analog input."
    // The JS side responds by auto-starting a poll at its default
    // interval (200 ms) — no pinMode/analogRead in the browser code.
    Pardalote.share(POT, ANALOG_INPUT_MODE);
}

void loop() {
    Pardalote.run();
    // Nothing else needed — the browser's poll requests are handled
    // by Pardalote.run() above, which also fires the analogRead and
    // broadcasts the result.
}

sketch.js — the browser side

const POT = 'A0';   // shared input — matches the Arduino sketch

const arduino = new Arduino();
setupConnection(arduino, { store: 'pardalote-shared-potentiometer' });

// Pin handles resolve alias strings like 'A0' lazily, so this listener can be
// registered right away — it starts firing once the board's alias table
// arrives with the connection handshake.
arduino.pin(POT).on('change', ({ value }) => {
    document.getElementById('value').textContent = value;
    const pct = (value / arduino.analogMax) * 100;
    document.getElementById('bar').style.width = pct + '%';
});

What this example demonstrates

The companion to shared-light-switch. That one showed the Arduino pushing values to the browser; this one shows the Arduino announcing a pin so the browser auto-starts polling — without any pinMode or analogRead call on the JS side.

The minimal Arduino sketch:

Arduino

void setup() {
    Pardalote.begin();
    pinMode(POT, INPUT);
    Pardalote.share(POT, ANALOG_INPUT_MODE);  // ← tells the browser
}

void loop() {
    Pardalote.run();
    // nothing else — the browser polls, Pardalote.run() handles it
}

The minimal browser sketch:

arduino.pin('A0').on('change', ({ value }) => updateDisplay(value));

No arduino.pinMode, no arduino.analogRead. The polling pipeline is set up automatically when the Arduino's share(A0, ANALOG_INPUT_MODE) arrives.

Hardware

Arduino UNO R4 WiFi or ESP32 development board
Potentiometer (10 kΩ is fine; anything in the 1 kΩ – 100 kΩ range works)

Wire it as a voltage divider:

Pot pin	Connect to
Outer 1	3.3 V
Wiper (centre)	A0
Outer 2	GND

Run it

In Arduino IDE: File → Examples → Pardalote → shared-potentiometer, select your board, upload.
Find the Arduino's IP from the LED matrix (UNO R4) or Serial Monitor (ESP32).
Open index.html and press Connect — enter the IP (or switch to USB). No code editing needed; the setting is remembered per browser.
Turn the pot. The number on screen and the bar should follow it in real time.

What's happening on the wire

Arduino: Pardalote.share(A0, ANALOG_INPUT_MODE)
       → CMD_PIN_MODE A0 = ANALOG_INPUT_MODE
Browser receives CMD_PIN_MODE:
       → starts a default-interval (200 ms) analogRead poll
       → CMD_ANALOG_READ A0 [interval=200]
Arduino registers the periodic action; every 200 ms:
       → reads A0, broadcasts CMD_ANALOG_READ A0 = <value>
Browser receives CMD_ANALOG_READ:
       → updates cache, fires arduino.pin('A0').on('change', …)
       → display updates

The JS code on the page is just the pin handle's 'change' listener. The rest of the pipeline was set up by the Arduino's one-line call to share().

Why this is useful

In a project where the Arduino sketch is the source of truth about which pins are wired to what (and the browser is just a viewer), share() lets the Arduino describe its hardware setup to the browser, instead of every browser sketch having to repeat the wiring knowledge.

Polling rate is 200 ms here (the browser's default). If you want different rates, the browser can override after connect with arduino.analogRead('A0', 50) — that just updates the interval; no need to re-declare the mode.