How to Use Adafruit ADS1115 16-Bit ADC: Examples, Pinouts, and Specs

The Adafruit ADS1115 (Part ID: 1085) is a high-precision analog-to-digital converter (ADC) designed to provide 16-bit resolution for accurate measurement of analog signals. It features four single-ended or two differential input channels, making it ideal for interfacing with sensors, potentiometers, and other analog devices. The ADS1115 communicates via the I²C protocol, ensuring compatibility with a wide range of microcontrollers, including Arduino and Raspberry Pi.

• Sensor data acquisition (e.g., temperature, pressure, light sensors)
• Precision voltage measurement
• Battery monitoring
• Data logging systems
• Industrial control systems

The following table outlines the key technical details of the Adafruit ADS1115:

The ADS1115 has six pins, as described in the table below:

1. Power Supply: Connect the VDD pin to a 3.3V or 5V power source, and the GND pin to ground.
2. I²C Communication: Connect the SCL and SDA pins to the corresponding I²C pins on your microcontroller. Use pull-up resistors (typically 4.7kΩ) on the SCL and SDA lines if not already present.
3. Address Configuration: Set the I²C address using the ADDR pin:
   • Connect to GND for 0x48 (default).
   • Connect to VDD for 0x49.
   • Connect to SDA for 0x4A.
   • Connect to SCL for 0x4B.
4. Optional Alert Pin: If needed, connect the ALERT/RDY pin to a GPIO pin on your microcontroller for interrupt-based alerts.

Below is an example of how to use the ADS1115 with an Arduino UNO to read a single-ended input:

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

// Create an ADS1115 object
Adafruit_ADS1115 ads; 

void setup() {
  Serial.begin(9600);
  // Initialize the ADS1115
  if (!ads.begin()) {
    Serial.println("Failed to initialize ADS1115!");
    while (1); // Halt execution if initialization fails
  }
  Serial.println("ADS1115 initialized.");
}

void loop() {
  // Read a single-ended input (channel 0)
  int16_t adcValue = ads.readADC_SingleEnded(0);
  
  // Convert the ADC value to voltage (assuming default gain ±6.144V)
  float voltage = adcValue * 0.1875 / 1000; // 0.1875 mV per bit
  
  // Print the voltage to the Serial Monitor
  Serial.print("Voltage: ");
  Serial.print(voltage);
  Serial.println(" V");
  
  delay(1000); // Wait 1 second before the next reading
}

• Use decoupling capacitors (e.g., 0.1µF) near the VDD pin to reduce noise.
• Ensure proper grounding to avoid measurement errors.
• Select the appropriate gain setting for your input voltage range to maximize resolution.
• Keep I²C lines as short as possible to minimize signal degradation.

1. ADS1115 Not Detected on I²C Bus

   • Solution: Verify the wiring of the SCL and SDA pins. Ensure pull-up resistors are present.
   • Tip: Use an I²C scanner sketch to confirm the device address.

2. Incorrect Voltage Readings

   • Solution: Check the gain setting and ensure the input voltage is within the selected range.
   • Tip: Verify that the input signal is properly connected and not floating.

3. No Output on Serial Monitor

   • Solution: Ensure the Serial Monitor baud rate matches the Serial.begin() setting in the code.
   • Tip: Check for errors in the code or wiring.

Q: Can the ADS1115 measure negative voltages?
A: Yes, but only in differential mode. The voltage difference between the two inputs must remain within the selected gain range.

Q: What is the maximum sampling rate of the ADS1115?
A: The maximum sampling rate is 860 samples per second (SPS) when configured for the highest data rate.

Q: Can I use the ADS1115 with a 3.3V microcontroller?
A: Yes, the ADS1115 is compatible with both 3.3V and 5V systems.

Q: How do I use the ALERT/RDY pin?
A: The ALERT/RDY pin can be configured to trigger an interrupt when a conversion is complete or when a threshold is exceeded. Refer to the ADS1115 datasheet for configuration details.