How to use ADS1115 16-Bit ADC Module with Raspberry Pi

Overview
In this comprehensive guide, we will explore the process of integrating an
ADS1115 16-bit ADC module
with the
Raspberry Pi
, a renowned single-board computer developed by the Raspberry Pi Foundation. The ADS1115 breakout board is a high-resolution
analog-to-digital converter (ADC)
that can be used in conjunction with
microcontrollers
and single-board computers such as Arduino, ESP8266/32, STM32, and of course,
the Raspberry Pi
While the Raspberry Pi provides a multitude of
digital I/O pins
, it lacks a
built-in ADC
, which means it cannot directly read analog signals. This can be a limitation for projects that require the interfacing of sensors or devices that output
analog signals
. By incorporating the ADS1115 module, which boasts a
16-bit ADC resolution
, the Raspberry Pi’s ability to handle analog inputs can be vastly expanded. With the ADS1115, the smallest voltage that can be measured is
5V / 65536
=
0.000076V (76uV)
, offering enhanced precision for your projects. If you want more precison up to 0.3uV, you may check
ADS1220 24-Bit ADC
Module.
In the tutorial, we will take a look into the
specifications
and
benefits
of the
ADS1115 module
, illustrate the necessary components and connections for
interfacing
it with the Raspberry Pi, and furnish a sample
Python code
to assist you in initiating this potent ADC enhancement.
Bill of Materials
To thoroughly understand the ADS1115 ADC Module when used with Raspberry Pi, we require the following components:
S.N.
Components
Quantity
Purchase Link

Raspberry Pi 4

Amazon
AliExpress

ADS1115 ADC Module

Amazon
AliExpress

10K Potentiometer

Amazon
AliExpress

Breadboard

Amazon
AliExpress

Connecting Wires

Amazon
AliExpress
ADS1115 Chip
The ADS1115 is a precision, low-power, 16-bit, I2Ccompatible, analog-to-digital converter IC.
Features of ADS1115
16-bit Resolution
Four (4) Channel Single-Ended or Two (2) Channel Differential Inputs
I

C Protocol Interface
Programmable Comparator
Wide Supply Range
Low Current Consumption
Continuous-Conversion Mode
Programmable Data Rate
Programmable Comparator
Single-Cycle Settling
Internal Low-Drift Voltage Reference
Internal Oscillator
Wide Operating Temperature Range
Available in Ultra-Small X2QFN Package
ADS1115 Pin Configuration
The below image shows the pin configuration of the ADS1115 chip.
Pin 1 is the ADDR pin that selects the I2C address for the chip.
Pin 2 is the Alert/Ready pin which serves as a data ready and alert signal.
Pin 3 is the GND terminal.
Pins 4, 5, 6 & 7 are the four (4) ADC input pins. We can use these pins as either four (4) single-ended inputs or two (2) differential inputs.
Pin 8 is the positive power supply pin which accepts 2.0 V to 5.5 V
Pins 9 and 10 are the terminals for the I2C interface, SDA and SCL respectively.
ADS1115 Functional Block Diagram
The below is the functional diagram for the ADS1115 Chip.
Initially a multiplexer selects the input signal. Then, the selected signal feeds into a Programmable Gain amplifier (PGA). The PGA can be programmed to provide amplification of small signals prior to conversion.
Subsequently, the input is converted by a 16-bit Delta Sigma converter. The converter uses its own built-in voltage reference and built-in oscillator in measuring the input signal. Finally, the result of the conversion goes into the I2C interface. Also, a comparator provides a signal to the external interface that the result is ready for fetching.
Typical Connections of the ADS1115
The principle I2C connections for the ADS1115 is shown in the image below.
The ADS1115 interfaces directly to standard mode, fast mode, and high-speed mode I2C controllers. Any microcontroller I2C peripheral, including master-only and single-master I2C peripherals, operates with the ADS1115.
For more information refer to
ADS1115 Datasheet
ADS1115 Module or Breakout Board
The ADS1115 comes with X2QFN & VSSOP package which can’t be used for prototyping. Therefore we need the ADS1115 Module or Breakout Board to use it with Raspberry Pi or Any other Microcontroller.
These modules are widely available from different manufacturers and are very inexpensive. They are breadboard friendly and can be easily used in prototyping and testing applications.
ADS1115 Module Pinout
The ADS1115 Module has a total number of 10 Pins.
Pin. No.
Pin Name
Pin Description

VDD
Power supply: 2.0V to 5.5V

GND
Ground

SCL
Serial clock input: Clocks data on SDA (used for I2C communication)

SDA
Serial data: Transmits and receives data (used for I2C communication)

ADDR
I2C address select (slave)

ALERT/RDY
Digital comparator output or conversion ready

AIN0
Differential channel 1: Single-ended channel 1 input or Negative input

AIN1
Differential channel 1: Single-ended channel 2 input or Negative input

AIN2
Differential channel 2: Single-ended channel 3 input or Positive input

AIN3
Differential channel 2: Single-ended channel 4 input or Negative input
ADS1115 Module Schematic
The schematic diagram shown above is Adafruit’s version of the ADS1115 module.
It follows the typical connection for the ADS1115 chip. The 10K ohms pull-up resistors are installed on the I2C and Alert pins. Also, there is a 1uF capacitor installed between the VDD pin and the GND which serves as a decoupling capacitor.
Interfacing ADS1115 Module with Raspberry Pi
Interfacing an ADS1115 module with a Raspberry Pi 4 is straightforward, as both devices use the I2C communication protocol. In this tutorial, we will guide you through the steps to connect and configure the ADS1115 with the Raspberry Pi 4.
Connect the VCC pin of the ADS1115 to the 3.3V pin of the Raspberry Pi.
Connect the GND pin of the ADS1115 to any GND pin on the Raspberry Pi.
Connect the SDA pin of the ADS1115 to the SDA pin of the Raspberry Pi.
Connect the SCL pin of the ADS1115 to the SCL pin of the Raspberry Pi.
You may connect the A0, A1, A2, and A3 pins of the ADS1115 to the sensors or devices whose analog values you want to read. In this example, we will use a 10K Potentiometer that can be connected to A0 Pin of ADS1115.
ADS1115 Python Library Installation
Before moving to the Python programming part, we need to install ADS1115 Library on Raspberry Pi.
Open a terminal window on your Raspberry Pi. Run the following command to install the ADS1x15 Python library.

sudo
pip3
install
adafruit
circuitpython
ads1x15
Python Code to Read Analog Value using ADS1115 & Raspberry Pi
Here is the Python Code to interface ADS1115 16-bit ADC Module with Raspberry Pi. The code will read analog value from Pin A0 fed using the potentiometer. You may use a
ADC Calculator
to manually calculate the ADC Value.
Copy the following code and paste it on the Thonny IDE editor window.

import
board
import
time
import
busio
import
adafruit_ads1x15
ads1115
as
ADS
from
adafruit_ads1x15
analog_in
import
AnalogIn
# Initialize the I2C interface
i2c
=
busio
I2C
(
board
SCL
board
SDA
)
# Create an ADS1115 object
ads
=
ADS
ADS1115
(
i2c
)
# Define the analog input channel
channel
=
AnalogIn
(
ads
ADS
P0
)
# Loop to read the analog input continuously
while
True
:
(
"Analog Value: "
channel
value
"Voltage: "
channel
voltage
)
time
sleep
(
0.2
)
Run the Code and you can see the following readings in Thonny Shell.
If the potentiometer is rotated to full position, the Thonny Shell shows 3.3V as full voltage.
If the potentiometer is rotated to zero position, the Thonny Shell shows 0V as voltage.
Python Code to Read Multiple Analog Values
The ADS1115 has 4 channel input. Hence, it can read 4 different analog values at the same time.
The following Python Code will read the multiple analog values from 4 different ADC pins A0, A1, A2, A3.

import
board
import
busio
import
adafruit_ads1x15
ads1115
as
ADS
from
ad