Analog data logging using Arduino

For fast analog data acquisition on an Arduino UNO, you can utilize the analogRead() function, but to optimize it for speed, we can:

1. Use Direct Register Manipulation to bypass the overhead of the `analogRead()` function.

2. Disable ADC interrupts if you're not using them.

3. Set the ADC prescaler to a value that allows faster conversions.

Here’s a code example that shows how to configure the Arduino UNO to acquire analog data very fast:

Fast Analog Data Acquisition Code

const int analogPin = A0;  // Analog input pin
const int numSamples = 1000; // Number of samples to acquire

// Variables to hold ADC results
volatile uint16_t analogData[numSamples];
volatile unsigned long lastMicros = 0;
volatile int sampleIndex = 0;

void setup() {
  Serial.begin(115200);  // Initialize Serial for output
  // Configure the ADC for fast conversion
  ADMUX = (1 << MUX0);    // Select A0 pin (MUX0 = 1)
  ADCSRA |= (1 << ADEN);  // Enable ADC
  ADCSRA &= ~(1 << ADIF); // Clear ADC interrupt flag
  ADCSRA |= (1 << ADATE); // Enable Auto Trigger
  ADCSRA |= (1 << ADPS2) | (1 << ADPS1);  // Set prescaler to 64 (fastest)
  ADCSRA |= (1 << ADSC);  // Start the conversion
  ADCSRA |= (1 << ADIE);  // Enable ADC interrupt

  // Configure the ADC to be in free-running mode
  ADCSRA |= (1 << ADATE); // Enable auto-triggering mode (free running)
  ADCSRB = 0;             // Free running mode

  sei();  // Enable global interrupts
}

void loop() {
  // We acquire data until numSamples is filled
  if (sampleIndex >= numSamples) {
    // Send the data to Serial when done
    for (int i = 0; i < numSamples; i++) {
      Serial.println(analogData[i]);
    }
    sampleIndex = 0;  // Reset for the next acquisition
  }
}

// ADC Conversion Complete ISR
ISR(ADC_vect) {
  if (sampleIndex < numSamples) {
    analogData[sampleIndex++] = ADC;  // Store the ADC result
  }
}

Key Optimizations:

1. Direct Register Manipulation:

   - Instead of using `analogRead()`, this code reads directly from the ADC register (`ADC`).

   - It sets the ADC prescaler to 64 for faster conversion, and uses `ADCSRA` for controlling ADC features.

2. Auto-trigger (Free Running Mode):

   - The ADC is set to continuous conversion mode, so it automatically triggers a new conversion after each one. This eliminates the need for manual triggering.

3. Interrupts for Fast Acquisition:

   - The `ADC_vect` interrupt is triggered every time an analog-to-digital conversion is complete, enabling fast acquisition without delay.

Prescaler Settings for ADC Clock:

The ADC clock in an Arduino UNO can be controlled using the prescaler, which divides the 16 MHz system clock to give the ADC a lower clock frequency. The prescaler is set in the `ADCSRA` register:

- Prescaler of 16 (default): 1 MHz

- Prescaler of 64: 250 kHz (faster, but higher noise)

- Prescaler of 128: 125 kHz (useful for higher precision but slower)

In the example, we used a prescaler of 64, which provides a balance between speed and accuracy.

Data Output:

- The `analogData` array will store all the ADC readings, and once the acquisition of the desired number of samples (`numSamples`) is complete, it sends the data over serial to the PC for analysis.

Notes:

- The code is designed for fast analog data acquisition. You can adjust the `numSamples` for longer or shorter acquisition.

- The resolution of the analog readings will be 10 bits (0-1023) as provided by the standard ADC in Arduino UNO.

- If you need higher speeds, consider moving to a more advanced board, such as Arduino Due or Teensy, which support faster ADCs.