How to Use ADS1115: Examples, Pinouts, and Specs

The ADS1115 is a high-precision 16-bit analog-to-digital converter (ADC) with an I2C interface. It is capable of measuring up to four single-ended inputs or two differential inputs, making it ideal for applications requiring accurate sensor data acquisition. The ADS1115 features a programmable gain amplifier (PGA), allowing it to handle a wide range of input voltages. Its small size and low power consumption make it suitable for portable and embedded systems.

• Sensor data acquisition (e.g., temperature, pressure, light sensors)
• Battery monitoring
• Industrial process control
• Portable instrumentation
• Data logging systems

• Resolution: 16-bit
• Input Channels: 4 single-ended or 2 differential
• Input Voltage Range: ±0.256V to ±6.144V (configurable via PGA)
• Supply Voltage: 2.0V to 5.5V
• Interface: I2C (up to 3.4 MHz)
• Programmable Data Rates: 8 SPS to 860 SPS (samples per second)
• Operating Temperature: -40°C to +125°C
• Low Power Consumption: 150 µA (typical)

The ADS1115 is typically available in an 8-pin package. Below is the pinout and description:

The ADS1115 supports up to four unique I2C addresses, determined by the ADDR pin configuration:

1. Power Supply: Connect the VDD pin to a 2.0V–5.5V power source and the GND pin to ground.
2. I2C Interface: Connect the SCL and SDA pins to the corresponding I2C lines of your microcontroller. Use pull-up resistors (typically 4.7kΩ) on both lines.
3. Input Signals: Connect your analog input signals to the AIN0–AIN3 pins. Configure the ADS1115 for single-ended or differential mode as needed.
4. Address Selection: Set the ADDR pin to configure the I2C address, ensuring it does not conflict with other devices on the bus.
5. Alert/Ready Pin: Optionally, use the ALERT/RDY pin for interrupt-driven applications or to monitor conversion readiness.

• Input Voltage Range: Ensure the input voltage does not exceed the configured PGA range or the supply voltage.
• Bypass Capacitor: Place a 0.1µF ceramic capacitor close to the VDD pin for noise filtering.
• I2C Pull-Up Resistors: Use appropriate pull-up resistors on the SDA and SCL lines to ensure reliable communication.

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 serial communication
  while (!Serial);    // Wait for Serial Monitor to open

  // 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 from 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 results
  Serial.print("ADC Value: ");
  Serial.print(adcValue);
  Serial.print(" | Voltage: ");
  Serial.print(voltage, 4); // Print voltage with 4 decimal places
  Serial.println(" V");

  delay(1000); // Wait 1 second before the next reading
}

• The Adafruit_ADS1X15 library is used for simplicity. Install it via the Arduino Library Manager.
• The default PGA setting is ±6.144V, resulting in a resolution of 0.1875mV per bit.

1. No I2C Communication:

   • Ensure the SDA and SCL lines are connected correctly.
   • Verify that pull-up resistors are present on the I2C lines.
   • Check the I2C address configuration and ensure it matches the software settings.

2. Incorrect Voltage Readings:

   • Confirm that the input voltage is within the configured PGA range.
   • Check for noise or interference on the input signal.
   • Verify the power supply voltage is stable and within the specified range.

3. ADS1115 Not Detected:

   • Ensure the ADDR pin is configured correctly for the desired I2C address.
   • Use an I2C scanner sketch to verify the device address.

• Use an oscilloscope or logic analyzer to monitor the I2C lines for proper communication.
• Double-check all connections and solder joints for continuity.
• Test the ADS1115 with a simple setup (e.g., single-ended input) before integrating it into a complex circuit.

By following this documentation, you should be able to successfully integrate and use the ADS1115 in your projects.