PROJECT 2 · ANALOG INPUT

Analog Inputs — Reading a Potentiometer

Measure a range of voltage (0–3.3 V) as a number 0–4095 with the ESP32's ADC.

⬇ Download the sketch Save Project_2_ESP32_Analog_Inputs.ino, then open it in the Arduino IDE (setup: Project 0b).

1 · Analog vs. digital, recapped

A digital input sees only HIGH or LOW (Project 1).
An analog input measures a continuous voltage 0–3.3 V and converts it to a number via the ADC.

The ESP32 ADC is 12‑bit, so readings run 0 … 4095:

0–3.3 V maps to 0–4095 — 0 V → 0 · 3.3 V → 4095 · in between → proportional.

The ADC pin here

We use GPIO 4 ANALOG (ADC2, channel 0) — the same physical pin that was a digital input in Project 1, now used with analogRead().

For later: GPIO 4 is on ADC2, which can't be read while Wi‑Fi is on. Fine here (no Wi‑Fi). In Wi‑Fi projects use an ADC1 pin (GPIO 32, 33, 34, 35, 36, 39).

2 · Parts

Qty	Part	Notes
1	ESP32 DEVKIT V1 · breadboard · jumper wires	—
1	Potentiometer (10 kΩ)	3 legs: two ends + a middle wiper

3 · Wiring

Potentiometer: outer legs to 3.3 V and GND, wiper to GPIO 4 — Outer legs → 3.3 V and GND · middle leg (wiper) → GPIO 4.

One outer leg → 3.3 V
Other outer leg → GND
Middle leg (wiper) → GPIO 4

Turning the knob taps off 0 V → 3.3 V, and the ADC reports the matching 0–4095 value.

4 · Code & expected serial output

The sketch prints the raw value and the voltage it represents. Open Serial Monitor at 115200:

==============================================
 Project 2: ESP32 Analog Inputs (ADC)
==============================================
Potentiometer -> GPIO 4
12-bit ADC: 0 = 0 V ... 4095 = 3.3 V
Turn the knob and watch the value change.
----------------------------------------------
Pot:    0 / 4095   (~0.00 V)
Pot: 2047 / 4095   (~1.65 V)
Pot: 4095 / 4095   (~3.30 V)

potValue = analogRead(potPin);            // 0 .. 4095
float voltage = potValue * 3.3 / 4095.0;  // convert to volts

Try the Serial Plotter (Tools → Serial Plotter, 115200): turning the knob draws a live graph — a great way to see the analog signal.

5 · The ADC isn't perfectly linear

ESP32 ADC voltage vs reading, non-linear at the ends — Readings flatten near 0 V and 3.3 V — you can't tell ~3.2 V from ~3.3 V.

This matters for precise measurements; for a knob or light sensor it's fine.

6 · Demonstration

Potentiometer on a breadboard with the ESP32 — Fully one way → 0 · fully the other → 4095.

7 · Troubleshooting

Symptom	Likely cause	Fix
Stuck at 0 or 4095	An outer leg not on 3.3 V / GND	Recheck both outer legs
Value jumps randomly	Wiper not on GPIO 4	Confirm middle leg → GPIO 4
Monitor blank / garbage	Wrong baud	Set it to 115200
Never reaches 4095	Normal ADC non‑linearity	Expected near the top