How to Use ADS1118 - ADC: Examples, Pinouts, and Specs

The ADS1118 is a high-precision, 16-bit analog-to-digital converter (ADC) manufactured by Texas Instruments. It features an integrated programmable gain amplifier (PGA) and operates over an I2C-compatible interface. This versatile component is designed for precision measurement applications, offering low power consumption and support for multiple input channels. Its compact VSSOP package makes it ideal for space-constrained designs.

• Temperature sensing (e.g., thermocouples, RTDs)
• Battery monitoring
• Portable medical devices
• Industrial process control
• Data acquisition systems

• Resolution: 16 bits
• Input Channels: 4 single-ended or 2 differential
• Input Voltage Range: ±0.256 V to ±6.144 V (configurable via PGA)
• Supply Voltage: 2.0 V to 5.5 V
• Interface: I2C-compatible
• Conversion Rate: Up to 860 samples per second (SPS)
• Operating Temperature Range: -40°C to +125°C
• Power Consumption:
  • Active Mode: 150 µA (typical)
  • Power-Down Mode: 0.5 µA (typical)
• Package: VSSOP-10

The ADS1118 is available in a 10-pin VSSOP package. Below is the pinout and description:

1. Power Supply: Connect the VDD pin to a stable power source (2.0 V to 5.5 V) and the GND pin to ground.
2. Analog Inputs: Connect the analog signals to the AINx pins. Configure the input mode (single-ended or differential) in the device's configuration register.
3. I2C Interface: Connect the SCL and SDA pins to the corresponding I2C lines of your microcontroller. Use pull-up resistors (typically 4.7 kΩ) on both lines.
4. Data Ready Signal: Optionally, use the DRDY pin to monitor when a conversion is complete.
5. Configuration: Program the ADS1118 via the I2C interface to set the desired gain, data rate, and input channel.

• Input Voltage Range: Ensure the input voltage does not exceed the configured PGA range or the device's absolute maximum ratings.
• Bypass Capacitor: Place a 0.1 µF ceramic capacitor close to the VDD pin for power supply decoupling.
• Thermocouple Applications: The ADS1118 includes an internal temperature sensor for cold-junction compensation, making it suitable for thermocouple measurements.
• I2C Address: The default 7-bit I2C address of the ADS1118 is 0x48.

Below is an example of how to interface the ADS1118 with an Arduino UNO to read a single-ended input:

#include <Wire.h>

// ADS1118 I2C address
#define ADS1118_ADDRESS 0x48

// Configuration register settings
#define CONFIG_REGISTER 0x8583  // Single-ended AIN0, ±4.096V, 128 SPS

void setup() {
  Wire.begin();  // Initialize I2C communication
  Serial.begin(9600);  // Initialize serial communication for debugging

  // Configure the ADS1118
  Wire.beginTransmission(ADS1118_ADDRESS);
  Wire.write(CONFIG_REGISTER >> 8);  // Send MSB of configuration register
  Wire.write(CONFIG_REGISTER & 0xFF);  // Send LSB of configuration register
  Wire.endTransmission();
}

void loop() {
  int16_t adcValue;

  // Request conversion result
  Wire.requestFrom(ADS1118_ADDRESS, 2);
  if (Wire.available() == 2) {
    adcValue = (Wire.read() << 8) | Wire.read();  // Combine MSB and LSB
  }

  // Convert ADC value to voltage (assuming ±4.096V range)
  float voltage = (adcValue * 4.096) / 32768.0;

  // Print the voltage to the serial monitor
  Serial.print("Voltage: ");
  Serial.print(voltage, 4);  // Print with 4 decimal places
  Serial.println(" V");

  delay(500);  // Wait 500 ms before the next reading
}

• The configuration register value (0x8583) sets the ADS1118 to read from AIN0 in single-ended mode, with a ±4.096 V range and a data rate of 128 SPS.
• Modify the configuration register value to change the input channel, gain, or data rate as needed.

1. No I2C Communication:

   • Ensure the pull-up resistors (4.7 kΩ) are connected to the SCL and SDA lines.
   • Verify the I2C address (0x48) matches the ADS1118's default address.
   • Check the wiring between the microcontroller and the ADS1118.

2. Incorrect Voltage Readings:

   • Confirm the input voltage is within the configured PGA range.
   • Verify the configuration register settings for the desired input mode and gain.
   • Ensure proper grounding and shielding to minimize noise.

3. Device Not Responding:

   • Check the power supply voltage (VDD) and ensure it is within the specified range.
   • Verify the I2C clock frequency does not exceed 400 kHz.

Q: Can the ADS1118 measure negative voltages?
A: Yes, in differential mode, the ADS1118 can measure negative voltages relative to the reference input.

Q: What is the maximum sampling rate of the ADS1118?
A: The maximum sampling rate is 860 samples per second (SPS).

Q: How do I use the internal temperature sensor?
A: Configure the ADS1118 to read from the temperature sensor by setting the appropriate bits in the configuration register. The temperature data is returned in the conversion result.

Q: Can I use the ADS1118 with a 3.3 V microcontroller?
A: Yes, the ADS1118 operates with supply voltages as low as 2.0 V, making it compatible with 3.3 V systems.

Q: Is the ADS1118 suitable for battery-powered applications?
A: Yes, the ADS1118's low power consumption (150 µA in active mode) makes it ideal for battery-operated devices.