Objective

The objective for this lab is to understand how to use Espressif DAC driver. Digital to Analog Converter (DAC) is a peripheral that converts digital signals to analog signals. The ESP32 has DAC of 8-bit resolution ranging from 0-255 bit value or 0.0-3.3V. ESP32 has only two DAC channels: channel 1 (GPIO 25) and channel 2 (GPIO 26). Students must generate a triangle wave with channel 1 and sine wave with channel 2.

Tasks	Description
Triangle Wave	create triangle wave with `GPIO 25`
Sine Wave	create sine wave with `GPIO 26`

GPIO Pin	DAC Channel
`GPIO 25`	Channel 1
`GPIO 26`	Channel 2

Digital	Analog
0	0.0 v
...	...
255	3.3 v

Bonus

Undergrad Bonus
- Replace triangle wave with a saw-tooth wave
Grad Bonus
- Modify sine wave to operate @ 10 hertz

ESP32 Pinout

                                        +-----------------------+
                                        | O      | USB |      O |
                                        |        -------        |
                                    3V3 | [ ]               [ ] | VIN
                                    GND | [ ]               [ ] | GND
    Touch3 / HSPI_CS0 / ADC2_3 / GPIO15 | [ ]               [ ] | GPIO13 / ADC2_4 / HSPI_ID / Touch4
CS / Touch2 / HSPI_WP / ADC2_2 /  GPIO2 | [ ]               [ ] | GPIO12 / ADC2_5 / HSPI_Q / Touch5
     Touch0 / HSPI_HD / ADC2_0 /  GPIO4 | [ ]               [ ] | GPIO14 / ADC2_6 / HSPI_CLK / Touch6
                        U2_RXD / GPIO16 | [ ]               [ ] | GPIO27 / ADC2_7 / Touch7
                        U2_TXD / GPIO17 | [ ]               [ ] | GPIO26 / ADC2_9 / DAC2
                     V_SPI_CS0 /  GPIO5 | [ ]  ___________  [ ] | GPIO25 / ADC2_8 / DAC1
               SCK / V_SPI_CLK / GPIO18 | [ ] |           | [ ] | GPIO33 / ADC1_5 / Touch8 / XTAL32
       U0_CTS / MSIO / V_SPI_Q / GPIO19 | [ ] |           | [ ] | GPIO32 / ADC1_4 / Touch9 / XTAL32
                SDA / V_SPI_HD / GPIO21 | [ ] |           | [ ] | GPIO35 / ADC1_7 
                 CLK2 / U0_RXD /  GPIO3 | [ ] |           | [ ] | GPIO34 / ADC1_6 
                 CLK3 / U0_TXD /  GPIO1 | [ ] |           | [ ] | GPIO39 / ADC1_3 / SensVN 
       SCL / U0_RTS / V_SPI_WP / GPIO22 | [ ] |           | [ ] | GPIO36 / ADC1_0 / SensVP 
               MOSI / V_SPI_WP / GPIO23 | [ ] |___________| [ ] | EN 
                                        |                       |
                                        |  |  |  ____  ____  |  |
                                        |  |  |  |  |  |  |  |  |
                                        |  |__|__|  |__|  |__|  |
                                        | O                   O |
                                        +-----------------------+

Example

Here is an example of a single DAC channel doing a square wave.

#include <stdio.h>
#include <math.h>
#include <driver/dac.h>
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
 
/* Create square wave */
void createSquareWave(void *pvParameters){
 
    /* Enable DAC output through channel 1 */
    dac_output_enable(DAC_CHANNEL_1);
    while(1){
        /* Generate square wave */
        dac_output_voltage(DAC_CHANNEL_2, 255); /* DAC max output: 3.3v */
        vTaskDelay(100/portTICK_PERIOD_MS); /* 100ms */
        dac_output_voltage(DAC_CHANNEL_2, 0);   /* DAC min output: 0v*/
        vTaskDelay(10/portTICK_PERIOD_MS); /* 100ms */
    }
}
 
void app_main(void){
    /* Create task */
    xTaskCreate(&createSquareWave, "createSquareWave", 4096, NULL, 5, NULL);
}

Lab Template

#include <stdio.h>
#include <math.h>
#include <driver/dac.h>
#include "freertos/FreeRTOS.h"
#include "freertos/task.h"
 
/* Triangle wave task */
void createTriangleWave(void *pvParameters)
{
    /* Enable DAC channel 1 */
    dac_output_enable(DAC_CHANNEL_1);
    /* create variable to store value */
    static int i = 0;
 
    while (1)
    {
        /* Generate triangle wave */
 
        /* output voltage through channel 1 */
        dac_output_voltage(DAC_CHANNEL_1, i);
 
        vTaskDelay(10 / portTICK_PERIOD_MS); /* 10 ms*/
    }
}
 
/* Sine wave task */
void createSineWave(void *pvParameters)
{
    /* Enable DAC channel 2 */
    dac_output_enable(DAC_CHANNEL_2);
    /* Variables to compute sine wave */
    static int i = 0;
    float val;
    int n = 0;
 
    while (1)
    {
        /* Compute sine wave */
        
 
        /* output voltage through channel 2 */
        dac_output_voltage(DAC_CHANNEL_2, n);
 
        vTaskDelay(10 / portTICK_PERIOD_MS);  /* 10 ms*/
    }
}
 
void app_main()
{
    /* Create tasks */
    xTaskCreate(&createTriangleWave, "createTriangleWave", 4096, NULL, 5, NULL);
    xTaskCreate(&createSineWave, "createSineWave", 4096, NULL, 5, NULL);
}

C helpful functions

For this Lab, there is two additional functions from Espressif that are important to use DAC peripheral. As previously mentioned, ESP32 has 2 DAC channels. The channel is enable by using: dac_output_enable(dac_channel_t channel). dac_channel_t is an enumeration that is provided down below. Please select the correct channel based on the GPIO pin and hardware.

typedef enum {
    DAC_CHANNEL_1 = 0,    
    DAC_CHANNEL_2 = 1,    
    DAC_CHANNEL_MAX,
} dac_channel_t;

Finally, the following function is use to produce a DAC output: dac_output_voltage(dac_channel_t channel, uint8_t dac_value). The DAC output value has a 8-bit resolution, please see the table provide in Objective section.

Additional Links

Authors

Jesus Minjares
- Master of Science in Computer Engineering
Erick Baca
- Master of Science in Computer Engineering

GitHub

Lab 8 Repository