How to use the DAC analog output in an ESP32

The digital-to-analog converter (DAC) is a component that converts a digital signal into a discrete analog signal.

The DAC takes digital numerical values and transforms them into voltage levels. This is particularly useful when you need to control reference voltages, generate custom waveforms, or even work with audio.

Unlike a pseudo-analog signal, such as the one we would get with a PWM, the DAC generates a “true” analog signal. Discrete (“jumping”), but “true” analog”.

The ESP32 and ESP32-S2 include two built-in DACs, allowing you to generate analog signals on two independent channels. These channels are known as DAC1 and DAC2, and can generate voltages in the range of 0 to 3.3 volts.

However, the ESP32-C3 and ESP32-S3 (and this is a real shame) do not include a DAC.

Using the DAC in the ESP32

Using the ESP32’s DAC in the Arduino environment is very simple. We just have to use the dacWrite function.

Let’s see a basic example of how to generate an analog signal using DAC1:

const int raw = 1500 * 255 / 3300;

void setup() {
  // DAC initialization
  dacWrite(DAC1, raw); // Generates a voltage of approximately 1.5V on DAC1
}

void loop() {
  // Nothing needs to be done in the main loop
}

In this example, the dacWrite() function is used to set the voltage value on the DAC1 channel.

The value passed as an argument is a number between 0 and 255, which corresponds to the voltage in the range of 0 to 3.3V. In this case, a voltage of approximately 1.5V is generated.

Generating more complex signals

While generating a constant voltage is useful, the DAC in the ESP32 can also be used to generate more complex waveforms. For example, we can generate a sine wave using a precalculated values table:

const int tableSize = 100;
const uint8_t sinTable[tableSize] = {127, 139, 150, ...}; // Precalculated values

int index = 0;

void setup() {
  // DAC configuration
}

void loop() {
  // Signal generation
  dacWrite(DAC1, sinTable[index]);
  index = (index + 1) % tableSize;
  delay(10); // Controls the frequency of the wave
}

In this example, a precalculated table of values is used to generate a sine wave in DAC1. The index is incremented to traverse the table and generate the waveform.