The ADS1115 is an ultra-compact, high-precision analog-to-digital converter (ADC) that provides 16-bit resolution over I2C. This module is essential for microcontrollers like the ESP8266 or Raspberry Pi that either lack built-in analog inputs or require higher precision than the standard 10-bit ADCs found on many Arduino boards. The purple board variant is a popular, robust implementation featuring an onboard power filter and pull-up resistors.

Specifications

• Resolution: 16-bit
• Operating Voltage: 2.0V to 5.5V DC
• Low Current Consumption: Continuous Mode: Only 150uA
• Programmable Data Rate: 8SPS to 860SPS (Samples Per Second)
• Interface: I2C with 4-pin selectable addresses
• Input Channels: 4 Single-Ended or 2 Differential inputs
• Internal PGA: Programmable Gain Amplifier (up to x16)
• Internal Voltage Reference: Low-drift

Features

• High Precision: Provides 65,536 levels of resolution, allowing for the detection of minute voltage changes that standard 10-bit (1,024 level) ADCs would miss.
• Programmable Gain (PGA): The built-in amplifier allows you to "zoom in" on small signals (as low as +/- 256mV) to use the full 16-bit range for maximum accuracy.
• Differential Inputs: Can measure the voltage difference between two pins (e.g., A0 and A1), which is excellent for reducing noise in sensor readings like load cells or thermocouples.
• I2C Addressable: By connecting the ADDR pin to GND, VCC, SDA, or SCL, you can use up to four of these modules on a single I2C bus for a total of 16 analog channels.
• Comparator Function: Includes a programmable comparator that can trigger the ALERT pin when a specific voltage threshold is crossed, allowing the MCU to stay in sleep mode until an event occurs.

Pin Configuration

• VDD: Power Supply (2.0V to 5.5V).
• GND: Ground.
• SCL: I2C Clock Line.
• SDA: I2C Data Line.
• ADDR: I2C Address Pin (Default GND for address 0x48).
• ALRT: Digital Alert/Interrupt output.
• A0-A3: Analog Input Channels.

Common Applications

• Battery Monitoring: Highly accurate voltage measurement for Li-Po or Lead-Acid battery management systems.
• Sensor Interfacing: Connecting analog sensors (gas, light, pressure) to digital-only microcontrollers.
• Industrial Process Control: Precision monitoring of 4-20mA loops or 0-5V signal lines.
• Portable Instrumentation: Used in handheld multimeters or data loggers where low power and high resolution are required.

Usage Tips

• Voltage Limit: Never apply a voltage to the analog pins (A0-A3) that exceeds VDD + 0.3V. Doing so can permanently damage the chip.
• I2C Pull-ups: The purple boards usually include 10k onboard pull-up resistors for SDA and SCL. If you are using multiple I2C devices, ensure the total pull-up resistance is not too low.
• Noise Reduction: For the most stable readings, place a 0.1uF ceramic capacitor between VDD and GND as close to the module as possible.
• Calibration: While the ADS1115 is very accurate, it is good practice to perform a two-point calibration in your code to account for any small offsets in your specific power supply.
• Note on DAC: While often searched alongside DACs, the ADS1115 is strictly an Analog-to-Digital Converter (ADC); it does not produce an analog output voltage. For DAC functionality, the MCP4725 is a common companion.