How to Use ADC0804: Examples, Pinouts, and Specs

The ADC0804 is an 8-bit analog-to-digital converter (ADC) manufactured by Texas Instruments, with the part ID ADC0804LCN. This component is designed to convert analog signals into digital data, making it an essential tool in data acquisition and processing systems. It operates with a single power supply and supports input voltages ranging from 0 to 5V. The ADC0804 features a parallel output for fast data transfer and is widely used in applications requiring precise analog-to-digital conversion.

• Data acquisition systems
• Microcontroller-based projects
• Signal processing
• Industrial automation
• Sensor interfacing (e.g., temperature, pressure, or light sensors)

The ADC0804 is a versatile and reliable ADC with the following key specifications:

The ADC0804 comes in a 20-pin Dual Inline Package (DIP). Below is the pinout and description:

1. Power Supply and Grounding:

   • Connect Vcc to a 5V power supply.
   • Connect AGND and DGND to the ground of the circuit.

2. Reference Voltage:

   • Connect a reference voltage to the Vref/2 pin. For a full-scale input range of 0–5V, connect Vref/2 to 2.5V.

3. Clock Signal:

   • Provide a clock signal to the CLK IN pin. This can be done using an external oscillator or by connecting a resistor to the CLK R pin for an internal clock.

4. Analog Input:

   • Connect the analog signal to be converted to the Vin(+) pin. Ensure the signal is within the 0–5V range.

5. Start Conversion:

   • Pull the WR pin low to start the conversion process.

6. Read Data:

   • Wait for the INTR pin to go low, indicating the conversion is complete.
   • Pull the RD pin low to read the 8-bit digital output from the D0–D7 pins.

• Ensure the analog input signal does not exceed the reference voltage to avoid inaccurate conversions.
• Use decoupling capacitors (e.g., 0.1 µF) near the power supply pins to reduce noise.
• If using the internal clock, select an appropriate resistor value for the CLK R pin to achieve the desired clock frequency.
• Avoid leaving unused pins floating; connect them to ground or a defined logic level.

Below is an example of how to interface the ADC0804 with an Arduino UNO to read an analog signal and display the digital output.

• Connect Vcc to the Arduino's 5V pin and AGND/DGND to the Arduino's GND.
• Connect the Vin(+) pin to the analog signal source.
• Connect the D0–D7 pins to Arduino digital pins 2–9.
• Connect CS, RD, and WR to Arduino digital pins 10, 11, and 12, respectively.
• Connect INTR to Arduino digital pin 13.

// Define ADC0804 pins
#define CS 10    // Chip Select
#define RD 11    // Read
#define WR 12    // Write
#define INTR 13  // Interrupt
#define D0 2     // Digital output pins D0–D7
#define D7 9

void setup() {
  // Configure control pins as outputs
  pinMode(CS, OUTPUT);
  pinMode(RD, OUTPUT);
  pinMode(WR, OUTPUT);
  pinMode(INTR, INPUT);

  // Configure data pins as inputs
  for (int i = D0; i <= D7; i++) {
    pinMode(i, INPUT);
  }

  // Initialize control pins
  digitalWrite(CS, HIGH);
  digitalWrite(RD, HIGH);
  digitalWrite(WR, HIGH);

  Serial.begin(9600); // Start serial communication
}

void loop() {
  // Start conversion
  digitalWrite(CS, LOW);
  digitalWrite(WR, LOW);
  delayMicroseconds(1); // Small delay for write pulse
  digitalWrite(WR, HIGH);

  // Wait for conversion to complete
  while (digitalRead(INTR) == HIGH);

  // Read digital output
  digitalWrite(RD, LOW);
  int digitalValue = 0;
  for (int i = D0; i <= D7; i++) {
    digitalValue |= (digitalRead(i) << (i - D0));
  }
  digitalWrite(RD, HIGH);

  // Print the digital value
  Serial.println(digitalValue);

  delay(500); // Delay for readability
}

1. No Output or Incorrect Data:

   • Verify the power supply connections (Vcc, AGND, and DGND).
   • Ensure the analog input signal is within the 0–5V range.
   • Check the reference voltage (Vref/2) and ensure it is correctly set.

2. Conversion Not Completing:

   • Confirm that the clock signal is present and within the required frequency range.
   • Check the WR and CS signals to ensure the conversion process is being triggered.

3. Noise in Output:

   • Use decoupling capacitors near the power supply pins.
   • Shield the analog input signal from external noise sources.

Q: Can the ADC0804 handle negative input voltages?
A: No, the ADC0804 is designed for unipolar input signals (0–5V). Negative voltages may damage the component.

Q: What is the purpose of the Vref/2 pin?
A: The Vref/2 pin sets the reference voltage for the ADC, determining the full-scale input range. For a 0–5V range, connect Vref/2 to 2.5V.

Q: Can I use the ADC0804 without an external clock?
A: Yes, you can use the internal clock by connecting a resistor to the CLK R pin. Select an appropriate resistor value to achieve the desired clock frequency.