112 lines
4.2 KiB
Markdown
112 lines
4.2 KiB
Markdown
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# Wave generator Example
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(See the README.md file in the upper level 'examples' directory for more information about examples.)
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This example demonstrates how to implement a software controlled signal generator by utilizing the DAC and Timer Group drivers. All waveforms demonstrated in this example are generated by software.
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Users can connect DAC output channel to their devices and use it as an simple analog signal output source.
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## How to use this example
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### Hardware Required
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* A development board with ESP32 SoC (e.g., ESP32-DevKitC, ESP-WROVER-KIT, etc.)
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* A USB cable for power supply and programming
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* A bunch of cables
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* Target device
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Make sure DAC output pin which is GPIO25 if channel 1 set, GPIO26 if channel 2 set, be connected to target device correctly.
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### Configure the project
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Under example folder, right click and select 'open terminal here'
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Execute following statements in terminal:
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```
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idf.py menuconfig
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```
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In `Example Configuration`, set the following options:
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#### DAC channel Num
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ESP32 DAC contains two channels:
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* **DAC_CHANNEL_1 (GPIO25), selected by default.**
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* DAC_CHANNEL_2 (GPIO26)
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#### Wave form
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This example demonstrates one of the following waveforms:
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* **Sine, selected by default.**
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* Triangle
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* Sawtooth
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* Square
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#### Wave frequency
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About this option:
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This signal generator has a range of frequency is 1kHz to 17kHz. **3kHz selected by default.**
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Modify the frequency will change the number of DAC output points. That will affect the smoothness of curve as well. Those output points are used to calculate the raw value(0~255) of each output point. All of these raw value are stored in an array.
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Based on the given frequency, the number of DAC output points for each cycle can be caluculated by following formula:
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```num_of_output_points = 1000000(us)/(7 us * frequency)```
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For example, with high frequency, 20kHz will results in generating only 10 output points, the curve will be sharp and zigzag.
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On the contrary, 500 Hz, low frequency relatively, will results in many DAC output points and the array cannot stores so many values that it will causes array overboundary.
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In short, there will be less output points per cycle in higher frequency, and more points in lower frequency.
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After got the raw value, the real output voltage can be calculated through following formula (VDD is 3.3V):
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```points_voltage = (VDD * DAC_OUTPUT / 255)```
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The voltage is in range of 0~3300mV.
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#### Enable output voltage log
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**Disabled selected by default.**
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If enabled, expected voltage of each points will be shown in terminal. It's intuitive for debugging and testing. If output example is needed, read **Example Output** chapter below.
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### Build and Flash
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After configure step is done, build project and flash it to the board:
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```
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$ idf.py -p PORT flash monitor
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```
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(To exit the serial monitor, type ``Ctrl-]``.)
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See the `Getting Started Guide` for full steps to configure and use ESP-IDF to build projects.
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## Example Output
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If oscilloscope is available, the target wave will show on oscilloscope after running this example.
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Additionally, if more specific output voltage information is needed, run menuconfig and set "Enable print output voltage" to "Enabled". Then, more information will show as log in terminal.
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For example, set wave frequency, waveform to 3kHz and sine respectively, and also enable print output voltage option. The output information will show in log in terminal as following:
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```
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I (318) Wave generator: DAC output channel: 1
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I (318) Wave generator: GPIO:25
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I (328) Wave generator: Waveform: Sine
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I (328) Wave generator: Frequency(Hz): 3000
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I (338) Wave generator: Output points num: 47
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I (438) Wave generator: Output voltage(mV): 1656
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I (538) Wave generator: Output voltage(mV): 1863
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I (638) Wave generator: Output voltage(mV): 2083
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I (738) Wave generator: Output voltage(mV): 2290
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I (838) Wave generator: Output voltage(mV): 2484
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I (938) Wave generator: Output voltage(mV): 2678
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I (1038) Wave generator: Output voltage(mV): 2834
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I (1138) Wave generator: Output voltage(mV): 2976
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I (1238) Wave generator: Output voltage(mV): 3092
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I (1338) Wave generator: Output voltage(mV): 3183
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....
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```
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`Output voltage` in log means real voltage, in mV, which is output through GPIO by device.
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