ADS1115 with ESP32: Analog Input, Gain & Voltage

Add an external analog input to an ESP32 using the ADS1115 I2C ADC module. The first exercise reads A0 with a known voltage before connecting a real sensor, battery divider or other analog source.

Identify ADS1115 and its input limits

Confirm the module is ADS1115, not the pin-compatible ADS1015. The ADS1115 class and voltage conversion depend on the selected device. Its programmable full-scale range describes conversion scaling; it does not authorize an analog pin to go beyond the powered device's supply rails. In this 3.3 V setup, keep input signals between GND and 3.3 V.

Prepare a known analog source

The controller for this example is an ESP32-C3 Supermini. Confirm that its USB upload and serial test works before adding the module. Use ESP32C3 Dev Module with USB CDC On Boot enabled for native USB, and open Serial Monitor at 115200 baud. Disconnect power while changing wires.

Start with A0 connected to GND. A floating analog input can produce unstable numbers even when I2C communication works. For a variable test, a potentiometer across 3V3 and GND with its wiper on A0 gives an input constrained to those rails.

Wire the ADC and A0

GPIO6 and GPIO7 are explicit assignments for this C3 example. They are not physical header positions or universal ESP32 defaults. For another board, select free exposed pins using its own pinout and update Wire.begin(). Keep ESP32 I2C pull-ups at 3.3 V.

Check both the input signal ground and ADC ground are common. The ADC offers four multiplexed single-ended inputs; that does not mean it samples all four simultaneously.

Install the ADS driver

In Arduino Library Manager install Adafruit ADS1X15 and Adafruit BusIO. Accept the required dependencies. Paste the complete example into a new sketch, click Verify, then Upload. If reporting a problem, include the board profile, package version and library version.

Use the Adafruit_ADS1115 object shown below. This example sets GAIN_ONE, a ±4.096 V conversion scale, while still powering the ADC at 3.3 V. Address selection can move the module within 0x48–0x4B; update begin() if your scan finds a different address.

Read counts and volts

Upload with A0 grounded and open Serial Monitor. Both the raw count and computeVolts() result are printed, avoiding a conversion factor copied from a different gain or ADC model.

#include <Arduino.h>
#include <Wire.h>
#include <Adafruit_ADS1X15.h>

Adafruit_ADS1115 adc;
void setup() {
  Serial.begin(115200);
  delay(1500);
  Wire.begin(6, 7); // ESP32-C3 Supermini example: SDA, SCL.
  if (!adc.begin(0x48, &Wire)) {
    Serial.println("ADS1115 not found.");
    while (true) delay(1000);
  }
  adc.setGain(GAIN_ONE); // +/-4.096 V scale; pins still must stay within supply rails.
}
void loop() {
  const int16_t raw = adc.readADC_SingleEnded(0);
  Serial.printf("A0: %d counts | %.4f V\n", (int)raw, adc.computeVolts(raw));
  delay(500);
}

Validate before connecting a sensor

1. Confirm A0 tied to GND reads near zero.
2. Power off, connect a known input within 0–3.3 V, then power on again.
3. Compare the reading with a meter referenced to the same ground.
4. Only then connect the intended sensor output and verify that its complete voltage range fits the ADC supply and selected gain.

For higher voltages, design and verify suitable signal conditioning first. Differential mode changes what is measured between two inputs; it does not remove each input's common-mode or supply limits. Resolution alone does not guarantee noise-free accuracy.

Troubleshooting

References and next steps

• TI ADS1115 product guidance
• Adafruit ADS1X15 driver
• ADC Arduino usage
• ESP32 I2C API

Related product

ADS1115 16 Bit I2C Module Precision ADC 4 Channel Development Board Pro Gain Amplifier 2.0V to 5.5V for Arduino →

Grove and alternative ADS1115 modules

This driver workflow also supports the related Grove ADS1115 and alternative ADS1115 listings once their connector, address strap and board-level supply are checked. Use the Grove signal labels on the Grove board; the generic breakout header order is not a Grove pinout. Never confuse VDD supply, selected PGA full scale and permitted analog-pin voltage. ADS1015 requires its own device class and scaling.

Related module variants in our store:

• 109020041 Data Conversion IC Development Tool Grove-ADS1115 16-bit ADC
• 16 Bit I2C ADS1115 Module ADC 4 Channel with Pro Gain Amplifier