(See the README.md file in the upper level 'examples' directory for more information about examples.)
## Overview
This example shows the basic usage of outputting continuous voltage by the DAC driver. There are two ways to realize continuous output, one is outputting by DMA transmission and another is by timer interrupt.
While using timer interrupt to output the waves, it actually sets the voltage by `oneshot` API in every timer interrupt callback. Which means the conversion frequency is equal to the timer interrupt frequency. Obviously, the conversion frequency is limited by the interrupt, which relies on the CPU scheduling, thus it can't reach a high frequency in this mode. But it can be used as a supplementary way while the conversion frequency is too low to use DMA mode.
While using DMA to transmit the wave buffers, the digital values are put into a DMA buffer waiting for transmission and conversion, that means the conversion frequency is equal to the frequency that DMA transmitting the data. We can set the DMA frequency directly, and the digital data in the buffer will be sent automatically when the buffer has been loaded into the DMA. So the conversion frequency can reach even several MHz while using DMA mode. But the wave can be distorted if the frequency is too high.
- Note that some ESP32-S2 DevKits have LED on it which is connected to GPIO18 (same pin as DAC channel1), so the output voltage of DAC channel 1 can't go down due the this LED.
* (Optional) An oscilloscope to monitor the output wave
### Configure the Project
You can switch the output method by setting the macro `EXAMPLE_DAC_CONTINUOUS_MODE` to `EXAMPLE_DAC_CONTINUOUS_BY_TIMER` or `EXAMPLE_DAC_CONTINUOUS_BY_DMA`.
There are four waves: sine, triangle, saw tooth and square. These waves are stored in corresponding buffers, and each wave has 400 points as default, which can be modified by `EXAMPLE_ARRAY_LEN`, reduce the point number can increase the wave frequency.
### Build and Flash
Note that as we use the ADC to monitor the output data, we need to set false to `CONFIG_ADC_DISABLE_DAC_OUTPUT` in the menuconfig, otherwise the ADC will shutdown the DAC power to guarantee it won't be affect by DAC.
Build the project and flash it to the board, then run monitor tool to view serial output:
```
idf.py -p PORT flash monitor
```
(Replace PORT with the name of the serial port to use.)
(To exit the serial monitor, type ``Ctrl-]``.)
See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.
## Example Output
This example can output sine wave, triangle wave, saw tooth wave and square wave periodically, each wave will last for 3 seconds.
The DAC channels can be read by ADC channels internally. The ADC read period is 500 ms, the following log is the raw ADC value read from the DAC channels. But since the ADC sample-rate is lower than the DAC output-rate, the sampling value can only indicate that the voltage is changing.
### Timer Triggered Output
You can see sine wave, triangle wave, saw tooth wave and square wave at 50 Hz on the oscilloscope.
```
I (333) dac continuous: --------------------------------------------------
I (343) dac continuous: DAC continuous output by Timer
I (343) dac continuous: DAC channel 0 io: GPIO_NUM_25
I (353) dac continuous: DAC channel 1 io: GPIO_NUM_26
I (353) dac continuous: Waveform: SINE -> TRIANGLE -> SAWTOOTH -> SQUARE
I (363) dac continuous: DAC conversion frequency (Hz): 20000
I (373) dac continuous: DAC wave frequency (Hz): 50
I (373) dac continuous: --------------------------------------------------
