#1 Arduino Uno R4 Wi-Fi Board - Using DAC output to dim/fade LED

 

RA4M1 microcontroller has 2-channels of 8-bit DAC and 1-channel of 12-bit DAC. 12-bit DAC has output amplifier and 8-bit DAC doesn’t have output amplifier. The 8-bit DAC output is given to the on-chip comparator as reference voltage. 12-bit DAC output is available on the A0 pin of the Arduino Uno R4 Wi-Fi. The range of the output is from 0 to 3.3V. 12-bit DAC is preferred for smooth LED fading. We can see the DAC output highlighted in green (P014_AN09_DAC) in the below snapshot of the schematic.

Pin (Arduino Connector)	MCU Pin	Functionality	Remarks
DAC0 (A0)	RA0	12-bit DAC, Analog In	True analog output, 0–3.3V, use for LED dimming
D2 – D13	-	Digital I/O, PWM capable	8-bit PWM output, can simulate analog voltage
D9, D10, D11, D12, D13	-	8-bit DAC output via PWM	Simulated analog output (not true DAC)

While using the A0 pin for the 12-bit DAC, unfortunately with the Arduino Core, it uses only 8-bit output and not full 12-bit. So, the maximum analog value of 3.3V on A0 pin will be reached for a value of 255 max. DAC value.

Below is the code for the same:

const int dacPin = A0;        // DAC0 pin

const int minDAC = 100;       // Minimum DAC value for LED to visibly glow

const int maxDAC = 200;      // Maximum DAC value (full brightness)

const int step = 1;          // Increment/decrement step

const int delayTime = 50;      // Delay in ms per step

void setup() {

  // No pinMode needed for DAC

  Serial.begin(9600);

  Serial.println("LED Fading Process");

  analogWrite(dacPin, maxDAC);

  delay(5000);

  analogWrite(dacPin, 0);

  delay(5000);

}

void loop() {

 

  // Fade up

  Serial.println("Fade Up started");

  for (int value = minDAC; value <= maxDAC; value += 10) {

    analogWrite(dacPin, value);

    delay(500);

    Serial.println("Fade up processing\n");

    Serial.println(value);

    }

  // Fade down

  Serial.println("Fade Down started");

   for (int value = maxDAC; value >= minDAC; value -= 10) {

    analogWrite(dacPin, value);

    delay(500);

    Serial.println("Fade down processing\n");

    Serial.println(value);

  }

}

Here is the link to the video from our YouTube Channel Way2Know: