ADS1115 16-Bit ADC Module: Complete Pinout, PGA Configuration & Sensor Interfacing Guide

Introduction to the ADS1115 16-Bit ADC Converter

Real – world signals such as temperature, pressure, weight, current, humidity, and pH can all be expressed as analog voltages. To process, record, or respond to these types of signals using a microcontroller, you need to convert the analog signal into a digital number using an Analog To Digital Converter (ADC). The accuracy of this conversion directly impacts how effectively a microcontroller can interpret the physical world.

Many popular microcontrollers, such as the Arduino Uno, ESP8266, etc., have their own built – in ADCs which are typically rated at 10 bits of resolution. At first, this seems enough, but in reality it only gives 1024 steps across the full voltage range. For a 5V system, that means each step is about 4.9 mV. For simple tasks like reading a potentiometer or detecting a switch press, this level of resolution is more than sufficient. However, for precise measurements, you may find that a 10 – bit ADC is limiting.  

For example, consider a load cell used in a kitchen scale. The signal variation of the bridge may be as low as 10-30 mV. In a 5V system, the ADC may not even be able to adequately resolve this signal variation. The ADC may only be able to register about 6 counts of variation over a range that should display hundreds.

The result is a scale that moves in 50-gram increments instead of the expected gram increments. This same problem arises in thermocouple amplifiers, pH sensors, strain gauges, and any system in which the relevant signal is a small fraction of the overall voltage range.

The Case for External High-Resolution ADCs

This is an issue that was addressed by the ADS1115 16-Bit ADC from Texas Instruments. An external 16-bit, high-precision ADC, the ADS1115 connects to a microcontroller using I²C, the same 2-wire protocol common to virtually all Arduino, Raspberry Pi, ESP32 or STM32 platforms with very little additional effort. Adding the ADS1115 to a design requires only four wires and minimal coding, but will dramatically enhance the ability of any embedded system to make measurements.

With a resolution of 16 bits, the input to the ADS1115 is divided into 65,536 discrete levels which is 64 times more precise than a conventional 10-bit ADC. In order to achieve the highest level of precision possible, the ADS1115 is configured using a gain of ±0.256V. For example, the ADS1115 16-Bit ADC provides an input range of ±2.048 Volts at the default setting, which corresponds to 62.5 µV between each of the 65,536 discrete input levels of the ADC.

When using the maximum gain ±0.256V full-scale, there is only 7.8µV between each of the ADC’s 65,536 discrete input levels. As an example, a change of 0.0016°C across a thermocouple junction will produce approximately 7.8uV; therefore, it will be possible to measure temperatures with an accuracy of this order using embedded applications based on the ADS1115.

Features:

Beyond resolution, the ADS1115 includes several features that distinguish it from a simple ADC chip:

• Programmable Gain Amplifier (PGA): An ADC can be calibrated to support a particular sensor output voltage with six selectable input ranges from ±0.256 V to ±6.144 V. This function simply allows an ADC to obtain the maximum number of useful bits relative to the output of any sensor regardless of its magnitude. 
• 4-channel input multiplexer (MUX): The ADC can sample up to four independent analog inputs in a sequential manner through one ADC core and, therefore, support up to four single-ended or two differential measurements per device. 
• Differential input mode: Noise rejection from measuring two input pin differences (e.g., between two pins) compared to measuring one input pin with respect to the ground is much better. This ability to measure how two pins vary with respect to each other is important for bridge sensors, current shunts and signals being sent across long cable runs.  
• Programmable data rate (8 to 860 samples per second): Longer conversion times result in having the chip perform more digital filtering thus providing lower output noise but slower measuring times. This functionality provides a significant advantage to performing precision measurements in electrically noisy environments.
• On-chip digital comparator: The ALERT/RDY pin can be configured to assert an interrupt when a measurement crosses a programmable threshold, enabling event-driven firmware without continuous polling.
• Ultra-low power consumption: At just 1.5 µA in single-shot idle mode, the ADS1115 is practical in battery-powered IoT sensor nodes where every microamp matters.
• Wide supply voltage range (2.0 V – 5.5 V): A single part works natively with 3.3 V systems (Raspberry Pi, ESP32, STM32) and 5 V systems (Arduino Uno, Mega) without modification.

Where the ADS1115 16-Bit ADC Is Used

The ADS1115 has become a standard building block across a wide range of engineering disciplines precisely because high-resolution analog measurement is a universal need:

• Industrial instrumentation — Pressure transducers, load cells, and flow sensors provide millivolt output that is derived from the Wheatstone bridge configuration. The differential input of the ADS1115, in combination with the high-gain PGA, represents the natural interface for these sensors in the microcontroller-based data acquisition systems.
• Environmental monitoring — Low-cost hardware with 16 bit resolution can accurately gather scientific data from pH probes, oxygen sensors, and conductivity sensors, which produce slowly-changing low-level voltages.
• Power systems and battery management — Shunt resistors can be used to provide highly-accurate voltage and current measurements and combined with the ADS1115’s ability to measure differential signals at millivolt levels will provide accurate state of charge calculations and coulomb counting in battery management systems.
• Medical and laboratory devices — Thermistor bridges, strain gauge weight scales, and electrochemical sensors all take advantage of the low noise, high resolution, and differential measurement capability of the ADS1115 16-Bit ADC.
• Maker and prototyping projects — For the hobbyist building precise measurement devices such as a weather station, load cell interface (an alternative to the HX711), soil moisture monitoring system, or even a customized thermocouple reader, the ADS1115 16-Bit ADC breakout board presents one of the most cost-effective paths to professional-grade analog measurement.

How the ADS1115 16-Bit ADC Compares to Built-in ADCs

To make the resolution advantage concrete, the table below compares the ADS1115 against the built-in ADCs found on common microcontroller platforms at equivalent input ranges.

A special note should be made about the internal ADC of the ESP32; while it is actually 12 bit capable, there are many people who have published information showing that it suffers from non-linearity, drift due to temperature and channel-to-channel variation. Consequently, in order to achieve consistent analog measurements, many projects that utilize the ESP32 use an external ADC, either the ADS1115 16-Bit ADC or ADS1015, thereby bypassing the internal ADC of the ESP32.

What This Guide Covers

This technical reference guide is meant for engineers, students, and makers who need to understand the ADS1115 sufficiently for proper utilization, not just to copy wire diagrams, but to grasp the reasoning behind each configuration choice and the compromises involved.

By reading this reference guide, users will be able to choose the proper PGA gain, wire the chip correctly for any microcontroller platform, write code to read the chip at the maximum 860 SPS throughput, and troubleshoot problems with measurement quality in their applications.

ADS1115 Architecture and Core Specifications

Understanding the internal architecture helps you choose correct settings and interpret measurement results. The ADS1115 16-Bit ADC is built around a second-order delta-sigma (ΔΣ) modulator followed by a digital decimation filter.

Delta-Sigma ADC Architecture

Delta-sigma converters operate by oversampling their input at very high speed while shaping the quantization noise to high frequencies for removal by a digital low-pass filter. This results in a high-resolution digital word being produced at a comparatively low data rate than that of a successive-approximation (SAR) ADC which samples and compares in discrete binary steps.

Key Architectural Advantages

• No sample-and-hold amplifier is necessary because the modulator continuously tracks the input signal
• The noise shaping moves the quantization noise outside of the signal band
• The decimation filter performs a built-in anti-aliasing function
• The differential input topology inherently provides common-mode rejection

Why ΔΣ Outperforms SAR for Precision Sensor Work

SAR ADCs can provide high sampling rates (to tens of megahertz) but the resolution of these devices is limited by the accuracy of the comparators used in them and by the matching of the DAC used to compose the samples.

The maximum resolution for a practical SAR ADC is typically about 18 bits. Delta-Sigma converters compromise throughput to gain high resolution and are traditionally used for instrumentation, medical, and industrial measurements at bandwidths <10 kHz.

Full Electrical Specifications

ADS111x Family Comparison

Texas Instruments offers three devices in the ADS111x family sharing the same pinout. Selecting the correct variant avoids paying for features you do not need.

ADS1115 vs ADS1015 — Resolution vs Speed Trade-off

The ADS1015 is the 12-bit sibling of the ADS1115 and is pin-for-pin and software-compatible. The choice depends on the application’s primary constraint.

ADS1115 Pinout — Every Pin Explained

The ADS1115 chip is available in two different package types; specifically, the VSSOP 10-pin and the X2QFN 10-pin package types. The breakout boards provide the same ten allocated pins but label them according to how they are used on the ADS1115 chip. The following pages will discuss: (1) pin functionality, (2) pin wiring requirements, and (3) common wiring mistakes.

Power Pins: VDD and GND

Supply Voltage and Decoupling

The ADS1115 16-Bit ADC can run from 2 V to 5.5V, so you can use it with either 3.3 V (like Raspberry Pi, ESP32, STM32) or 5 V (e.g. Arduino Uno) without needing to level shift the power rail. The I²C logic level is determined by the VDD — refer to Section 3.3 for information on level shifting.

• Place a 100 nF ceramic capacitor close to the VDD pin; length of leads is important.
• Add a 10 µF bulk electrolytic capacitor at the same supply node
• If you have a breakout board that has a separate AVDD pin, connect both the VDD and AVDD pins to the same supply node unless otherwise directed by the breakout board documentation.

Analog Input Pins: AIN0 – AIN3

Single-Ended Mode

When in single-ended mode, an AIN pin is selected to be measured against GND. The chosen AIN pin connects through the internal MUX to the positive input of the PGA, while GND connects to the negative input of the PGA. The ADC outputs a signed two’s complement value of 16 bits; the effective resolution for single-ended measurements is actually 15 bits of measurement range (0 to +32,767 counts) since the sign bit cannot be used.

Differential Mode

Differential mode measures the voltage differences between two AIN pins. This mode is the best choice for bridge sensors (i.e., strain gauges; load cells; pressure sensors) and long cable runs where common mode noise must be rejected. The full range of ±32,767 counts support the full 16-bit signed resolution.

I²C Bus Pins: SCL and SDA

Pull-up Resistor Requirements

I²C is an open-drain bus — both SDA and SCL require pull-up resistors to VDD. The correct resistor value depends on bus speed and total bus capacitance.

Logic Level Compatibility

Both pins on the ADS1115 are referenced to VDD. With a VDD of 3.3V, as in the case of a Raspberry Pi, you can connect I²C devices without level shifting because the SDA and SCL lines are compatible (3.3V logic). With VDD of 5V, as on Arduino Unos, the SDA and SCL pins are tolerant of 5.0V signals on most Arduinos, however caution must be used when using any microcontroller that is only rated for 3.3V such as an ESP32.

ADDR Pin: Configuring the Four I²C Addresses

The ADDR pin selects one of four I²C device addresses, allowing up to four ADS1115 devices to coexist on a single bus. This provides 16 single-ended channels or 8 differential channels from one MCU I²C port.

ALERT/RDY Pin: Comparator and Conversion-Ready

Pin Characteristics

ALERT/RDY is an open-drain output that requires an external pull-up resistor (typically 10 kΩ to VDD). It operates in two distinct modes controlled by the Config register.

Comparator Mode

When operating in Comparator Mode, Upon crossing the user-defined threshold set in the Low and High Threshold registers, the comparator pin asserts a Low signal thus allowing the ADS1115 to operate autonomously as an alarm device without the need for any additional firmware polling required by the ADS1115.

Conversion-Ready (RDY) Mode

The above implementation is to be enabled by setting both the low threshold of Lo_Thresh to 0x8000 and the high threshold of Hi_Thresh to 0x7FFF. Upon setting these two values to their defined limits, an ALERT/RDY low pulse will occur for one full conversion-length cycle every time new data is ready from the ADC. This enables an interrupt driven method of reading data at full 860 SPS sampling rate without the need for any polling wait period.

Programmable Gain Amplifier (PGA) Configuration

Choosing the PGA for the purposes of measurement accuracy is the most crucial decision that you will make when designing an instrument. By choosing the Full Scale Range of your measurement to match the output of the sensor(s) you are using, you’ll maximize the number of usable Least Significant Bits (LSB) and therefore maximize the effective resolution of your measurement.

PGA Gain Settings and Full-Scale Range

Selecting the Optimal Gain for Your Sensor

Matching FSR to Sensor Output

The goal is to choose the smallest FSR that still encompasses the full expected output range of your sensor. A sensor with a 0–100 mV output range should use the ±0.256 V FSR (7.8 µV LSB) rather than the ±4.096 V FSR (125 µV LSB) — the resolution improvement is 16×.

Config Register Deep-Dive

Config Register Map (Address 0x01)

The 16-bit Config register controls all operating parameters of the ADS1115 16-Bit ADC. Write it in two bytes (MSB first) over I²C.

Data Rate Register Values

 Interfacing ADS1115 with Arduino

Hardware Wiring

Arduino Uno and Arduino Mega Pin Connections

Reading Single-Ended Channels

Library Installation and Initialisation

Install the Adafruit ADS1X15 library via the Arduino Library Manager (search: “ADS1X15”). This library supports both ADS1015 and ADS1115 with an identical API.

#include <Wire.h>
#include <Adafruit_ADS1X15.h>
 
Adafruit_ADS1115 ads;  // Default I2C address 0x48
 
void setup() {
  Serial.begin(115200);
  // Set gain: GAIN_TWOTHIRDS = ±6.144V, GAIN_ONE = ±4.096V,
  // GAIN_TWO = ±2.048V (default), GAIN_FOUR = ±1.024V,
  // GAIN_EIGHT = ±0.512V, GAIN_SIXTEEN = ±0.256V
  ads.setGain(GAIN_ONE);  // ±4.096V FSR
  if (!ads.begin()) {
    Serial.println("ADS1115 not found. Check wiring.");
    while (1);
  }
}
 
void loop() {
  int16_t raw = ads.readADC_SingleEnded(0);  // Read AIN0
  // Convert to voltage: raw * FSR / 32768
  float voltage = raw * (4.096f / 32768.0f);
  Serial.print("AIN0: "); Serial.print(raw);
  Serial.print(" counts | "); Serial.print(voltage, 4);
  Serial.println(" V");
  delay(500);
}

Reading Differential Channels

// Differential read: AIN0 minus AIN1
// Returns signed int16: range -32768 to +32767
int16_t raw_diff = ads.readADC_Differential_0_1();
 
// With GAIN_SIXTEEN (FSR = ±0.256V), LSB = 7.8125 µV
float voltage_diff = raw_diff * (0.256f / 32768.0f);
Serial.print("Differential: "); Serial.print(voltage_diff * 1000.0f, 3);
Serial.println(" mV");

Interrupt-Driven Reads Using ALERT/RDY

Configuring the ADS1115 for RDY Mode

Polling the ADS1115 in a tight loop  wastes MCU cycles as well as limiting the system’s throughput. Instead, using the ALERT / RDY pin as an interrupt, the MCU can perform other tasks between conversions and ensures that each sample is read at the same output rate as the ADS1115.

volatile bool newDataReady = false;
 
void IRAM_ATTR rdyISR() {
  newDataReady = true;
}
 
void setup() {
  Serial.begin(115200);
  ads.setGain(GAIN_ONE);
  ads.begin();
 
  // Enable RDY mode: set Lo_thresh = 0x8000, Hi_thresh = 0x7FFF
  ads.startADCReading(ADS1X15_REG_CONFIG_MUX_SINGLE_0, true); // continuous
  // Wire ALERT/RDY to MCU INT pin with 10k pull-up
  pinMode(2, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(2), rdyISR, FALLING);
}
 
void loop() {
  if (newDataReady) {
    newDataReady = false;
    int16_t raw = ads.getLastConversionResults();
    float v = raw * (4.096f / 32768.0f);
    Serial.println(v, 4);
  }
  // MCU is free to do other work here
}

Interfacing ADS1115 with Raspberry Pi

Enabling I²C and Wiring

Raspberry Pi I²C Setup

1.     Run sudo raspi-config → Interface Options → I2C → Enable

2.     Reboot: sudo reboot

3.     Verify detection: sudo i2cdetect -y 1 — ADS1115 should appear at 0x48

4.     Install Python library: pip3 install adafruit-circuitpython-ads1x15

Python Code with CircuitPython ADS1x15 Library

import board
import busio
import adafruit_ads1x15.ads1115 as ADS
from adafruit_ads1x15.analog_in import AnalogIn
 
# Initialise I2C bus and ADS1115
i2c = busio.I2C(board.SCL, board.SDA)
ads = ADS.ADS1115(i2c)        	# Address 0x48 by default
ads.gain = 1                   	# GAIN_ONE = ±4.096 V FSR
 
# Single-ended channel reads
ch0 = AnalogIn(ads, ADS.P0)   	# AIN0 vs GND
ch1 = AnalogIn(ads, ADS.P1)   	# AIN1 vs GND
 
print(f"AIN0: {ch0.value} counts | {ch0.voltage:.4f} V")
print(f"AIN1: {ch1.value} counts | {ch1.voltage:.4f} V")
 
# Differential read: AIN0 minus AIN1
ch_diff = AnalogIn(ads, ADS.P0, ADS.P1)
print(f"Differential: {ch_diff.voltage*1000:.3f} mV")

Connecting Multiple ADS1115 Devices on One I²C Bus

Instantiating Multiple Devices in Python

import board, busio
import adafruit_ads1x15.ads1115 as ADS
from adafruit_ads1x15.analog_in import AnalogIn
 
i2c = busio.I2C(board.SCL, board.SDA)
 
# Device 1: ADDR → GND  →  0x48
ads_a = ADS.ADS1115(i2c, address=0x48)
# Device 2: ADDR → VDD  →  0x49
ads_b = ADS.ADS1115(i2c, address=0x49)
# Device 3: ADDR → SDA  →  0x4A
ads_c = ADS.ADS1115(i2c, address=0x4A)
# Device 4: ADDR → SCL  →  0x4B
ads_d = ADS.ADS1115(i2c, address=0x4B)
 
# Now read all 16 single-ended channels
devices = [ads_a, ads_b, ads_c, ads_d]
for dev_idx, dev in enumerate(devices):
    for ch_idx in [ADS.P0, ADS.P1, ADS.P2, ADS.P3]:
        ch = AnalogIn(dev, ch_idx)
        label = f"Dev{dev_idx+1}_AIN{ch_idx}"
        print(f"{label}: {ch.voltage:.4f} V")

High-Resolution Sensor Interfacing: Practical Examples

Temperature Measurement via Thermocouple Amplifier

Circuit: Type-K Thermocouple + AD8495 + ADS1115

The AD8495 is a precision thermocouple amplifier that outputs 5 mV/°C with internal cold-junction compensation. This voltage is well-suited for the ADS1115 with the ±0.512 V PGA setting.

ads.setGain(GAIN_EIGHT);  // ±0.512V FSR, LSB = 15.625 µV

int16_t raw = ads.readADC_SingleEnded(0);  // AD8495 OUT → AIN0

float voltage_mV = raw * (512.0f / 32768.0f) * 1000.0f;  // millivolts

float temperature_C = (voltage_mV - 1250.0f) / 5.0f;  // 1250 mV = 0°C offset

Serial.print("Temperature: ");
Serial.print(temperature_C, 2);
Serial.println(" °C");

Strain Gauge / Wheatstone Bridge (Differential Mode)

Specifically, when using a stable voltage source, a Wheatstone bridge produces a small output voltage that varies based on the amount of strain applied. To illustrate, a bridge powered with a 5 V excitation and a 10 kΩ strain gauge may produce an output in the range of 1 mV to 5 mV, depending on the measurement conditions. For this reason, the ADS1115’s differential input is well-suited for handling these small signals due to its built-in programmable gain amplifier (PGA), which allows accurate measurement of low-level voltages.

Noise Averaging Strategy

// 64-sample averaging to reduce noise floor by ~8x (1/sqrt(64))
const int NUM_SAMPLES = 64;
long sum = 0;
for (int i = 0; i < NUM_SAMPLES; i++) {
    sum += ads.readADC_Differential_0_1();
    delay(1);  // ~1 ms between samples at 860 SPS
}
int16_t averaged = (int16_t)(sum / NUM_SAMPLES);
float grams = (float)averaged * GRAMS_PER_COUNT;  // calibrate GRAMS_PER_COUNT

Current Sensing with a Shunt Resistor

Low-Side Current Measurement

Connect a low-resistance shunt resistor (10 mΩ – 100 mΩ) in series with the load return path. Measure the differential voltage across the shunt with the ADS1115 16-Bit ADC AIN0/AIN1 differential input and the ±0.256 V PGA setting.

Battery Voltage Monitoring with Resistor Divider

For voltages above VDD, a resistor divider scales the battery voltage to within the ADS1115 input range. Use precision 0.1% resistors to maintain the accuracy the 16-bit ADC provides.

 Noise, Accuracy, and Signal Integrity

Effective Resolution vs Nominal Resolution

The ADS1115 is a 16-bit ADC. Realistically, the effective number of bits (ENOB), for a certain data rate and environment (e.g. the PCB), will vary. For example, if you had an ADS1115 with a data rate of 860 SPS in a typical prototype environment, you would typically get around 14-15 ENOB. However, if you reduce the data rate to 8 SPS (the max decimation filter depth), it is possible to achieve an ENOB up to approximately 15.5.

PCB Layout Best Practices

Critical Layout Rules

• Place a 100 nF (X7R) ceramic decoupling capacitor as close as possible (within 2 mm) to the VDD pin.
• Add a 10 µF bulk capacitor (either tantalum or electrolytic) at the point where power enters the ADS1115 circuit.
• Keep the AIN traces as short as possible. Every millimeter contributes approximately 1 pF of capacitance (the longer the trace, the higher the capacitance).
• Do not route any digital signals (e.g., SDA, SCL, PWM, clock lines) in parallel with the AIN traces.
• Mount the ADS1115 16-Bit ADC close to the connector for the sensor and away from any switching voltage regulator.
• Use a solid analogue ground plane below the ADS1115, connecting to the digital ground plane at a single point only.
• For high-impedance source AINs (> 10 kΩ), place a 100 nF capacitor between AIN and GND to filter out RF interference

Software Noise Reduction Strategies

// Exponential Moving Average (EMA) filter
// alpha = 0.1 gives more smoothing; alpha = 0.5 tracks faster changes

float ema = 0.0f;
const float alpha = 0.1f;

void loop() {
  float raw_v = ads.readADC_SingleEnded(0) * (4.096f / 32768.0f);
  ema = alpha * raw_v + (1.0f - alpha) * ema;
  Serial.println(ema, 4);
  delay(10);
}

Troubleshooting Common Issues

Conclusion: When to Use the ADS1115

Summary Decision Matrix

Key Takeaways

• The ADS1115 outputs 16-bits of resolution up to 860 samples per second from a 2-5.5V power supply via I²C
• The PGA FSR should always be selected to match your sensor’s output range for maximum effective bits.
• Bridge sensors should be connected to the ADS1115 in a differential mode because single ended mode will lose the sign bit (i.e. the 15th bit).
• A maximum of four ADS1115 devices can be connected together with an I²C bus because they share the ADDR pin for a total of 16 channels.
• Increase real-world ENOB and analog performance by decreasing the sample rate, increasing the decoupling capacitors, and implementing software averaging of multiple samples.
• The Adafruit ADS1X15 Arduino and CircuitPython libraries use the same API for both platforms, making it easier to migrate from one platform to another.

Frequently Asked Questions