ESP32 Audio Output Using I2S and built-in Digital to Analogue Converters (DACs)

Hey Everyone, we're back with another  video about the ESP32 and audio output. In previous videos, we've covered  using the ESP32's I2S peripherals   along with the built-in Analogue to  Digital Converters for reading audio data. We've also looked at using the I2S peripherals  for directly outputting digital audio signals. In this video, we're going to take a look at  using the built-in Digital to Analogue Converters. We'll use these to output analogue  signals directly from the ESP32. So, there are a few things to note about the  Digital to Analogue Converters on the ESP32. There are two channels available DAC-1 and DAC-2. Both these channels support 8-bit resolution so  we can set them to a value between 0 and 255. The range of the output voltage  is from 0v volts to Vdd. So, typically a range of 0 volts to 3.3 volts. And one big difference from what you may  be used to is that the GPIO pins are fixed. Channel 1 will output on GPIO25 and  channel 2 will output on GPIO26. Basic output using Arduino  code is pretty straightforward. We just use the "dacWrite"  function specifying pins 25 or 26   along with the value that you would like to send. If you want to stick to the IDF functions  this is also very straightforward. You just need to enable the DAC channel  and then call "dac_output_voltage". DAC channel 1 will output on pin 25 and  DAC channel 2 will output on pin 26. Let's have a look at this in action. I've hooked up my multimeter to one of my esp32  dev boards and I'm slowly stepping up the voltage   on the output of the DAC channel. Here you can see a chart of the expected  values versus the measured values. There's a couple of things to note: We don't get zero volts when the output is  set to zero we get around four millivolts. There is a reasonably linear range up to about  1.5 volts where the error is fairly small. And then we increasingly get   differing values from what we expect as  we approach the maximum output voltage. If you're doing anything that requires any  accuracy it's probably worth calibrating   your own device to see what values you get. So, using direct output is pretty good if you  just want to output a slowly changing value. But what If you want to play audio  or generate high-frequency signals. For this, we can use the I2S  peripheral to transfer data using DMA. This will let us queue up samples to be   output letting the CPU get on  with doing other processing. We need to configure the I2S peripheral to  use the built-in Digital to Analog Converters. We need to tell it the sample rate  we want to use and bits per sample. This is slightly strange as only the  top eight bits will be used by the DACs. Initializing the I2S peripheral  is the same as usual. We install the driver - there is one important note here: we can only use I2S0 with the built-in DACs. We also need to set the I2S peripheral into  DAC mode and enable both the DAC channels. Sending data to the I2S  peripheral is straightforward   and follows the same pattern as we've used before. We create a task and within our task wait  for the peripheral to request more data. We can then write more data to the peripheral for output. Now the output from the DAC's won't be  powerful enough to drive a speaker directly   so you'll need an amplifier. I'm using a small breakout board with  an audio amplifier but you can easily   build a simple amplifier from discrete components. Let's have a listen to see how well this works. 🎵Music🎵 There's a bit of noise but that's probably  to be expected when building up a circuit   on a breadboard - we're not  dealing with high-end audio here. What about outputting arbitrary  signals and higher frequencies? I've tried a few experiments  outputting a simple sawtooth   waveform and this is the highest  frequency I was able to achieve. This works out at a sample rate of around 2 MHz  so you can output at fairly high frequencies. So, what have we learned? We can use the built-in  Digital to Analog Converters   to output analogue signals  directly from the ESP32. We can output audio data and we can output  arbitrary signals at reasonably high frequencies. The outputs are reasonably  linear over a range of values   but we are limited to 8-bit resolution so  high-end audio is probably not an option. Apart from that, this is a pretty simple  way to get analogue data out of the esp32. So thanks for watching all the source code is  on GitHub - the link is in the description. If you found this video useful then  please hit the subscribe button. There are more videos in the pipeline  and I'm working on an interesting project   which will hopefully use some of  what we've learned in this video. So thanks again and I'll  see you in the next video!

Channel: atomic14

Views: 11,457

Keywords: ESP32 audio, esp32 i2s, esp32 dac audio, esp32 dac example, esp32 dac pins, esp32 digital to analog converter, audio amplifier, esp32 projects, class-d amplifier, esp32 audio streaming, esp32 audio kit, esp32 audio output, esp32 audio player, esp32 dac audio, esp32 dac audio library, esp32 dac audio example, esp32 dac, esp32 audio recording, esp32 i2s dac, esp32 i2s adc, esp32 microphone, esp32 analog input

Id: lgDu88Y411o

Length: 6min 6sec (366 seconds)

Published: Thu Dec 31 2020

Reddit Comments

[u/dilznick5]

Awesome video! Was looking for something exactly like this a few months back. Saving for the future!