Category: Streaming

Encouraged by the happy ending of the Swinging Needles project, I decided to revisit an earlier audio spectrum analyzer. This time, instead of programmatically processing analog signals, I used a VS1053 plugin to let the chip do the Fourier stuff.

Before even starting to read actual frequency band values, I wanted to test my sketch by reading the plugin’s default frequency settings from VS1053’s memory. However, some of these readings made no sense at all, up to the point that I suspected a faulty chip. It took me some time to find out that the chip needs a few seconds of audio input before it will tell you something useful, even if it concerns a fixed setting like number of frequency bands.

Once the above mystery was solved, things became very straightforward. What a versatile chip this VS1053 is! While playing a 320 Kbps internet radio station, it can easily handle 14 frequency bands and let an esp8266 at 160 MHz show the results on a 128×64 Oled display. Part of the credits should go to the authors of the libraries that I used.

 

First impression produced by the sketch below; better videos with sound (and colors?) will follow.

 

Here’s an esp8266 demo sketch for a basic internet radio (fixed station, no metadata, no audio buffer), just to show a 14 band spectrum analyzer on a 128×64 SH1106 Oled display. Used pins are for the rather rare Wemos D1 R1, so you’ll probably have to change them.

 

This is the content of the plugin.h file that needs to be in the directory of the sketch:

 

 

 

 

…finally!

It took me some time (and strong coffee), but I finally managed to have the ESP32 version of my Internet Radio drive two vintage style analog VU meters!

 

And here they are…

Web browser controlled prototype with basic display and no matrix keypad attached

Soon after I had purchased a rather obscure VU meter kit, it turned out that the driver board was completely useless because it was mono (Chinese for stereo?).

So I decided to have the ESP32 read the analog (DC-biased) line out signals from the VS1053 mp3 decoder, map the peak-to-peak readings to [0,255] scaled values and send these to the ESP’s DACs for driving the meters. However, I couldn’t figure out how to do that without having to connect the VS1053’s floating audio ground to the system ground, which, so I guessed, would either not work, cause noise or even damage something.

Then I remembered the VU meter plugin for the VS1053, enabling you to read dB levels from a memory register. But these plugin readings are leaking peak dB levels, so I started wondering if it was possible to use them for reconstructing instantaneous dB levels. Not suitable for audio purists, but I wouldn’t mind if the result was convincing. After all, these cheap Chinese meters will never behave like professional VU meters anyway.

So I wrote a simple algorithm with some tuning parameters and functions for scaling and smoothing, calculated resistor values for limiting current to my meters to 0.4 mA max, added (probably unnecessary) flyback diodes to protect the ESP32 from negative voltage spikes, and just gave it a try. Here’s the wiring that I used for the meters.

The first result looked surprisingly good: the needles eagerly followed every move and twist of the music. Since everything is controlled by an algorithm, any desired meter ballistics can be easily simulated without electronics.

For now, further fine tuning seems unnecessary. Besides, a more audiophile approach already crossed my mind: have a FreeRTOS task listen in to the mp3 stream while it’s being sent to the VS1053, and programmatically decode it. That will allow me to extract true dB levels and could even become a replacement for the VS1053 board. Like I recently read in an article about Software Defined Radio (SDR), “software is the new hardware“.

Anyway, music finally looks almost as good again as it did in my youth. Let’s just hope for an analog VU meter revival soon. And how about a global rediscovery of reel-to-reel tapedecks (with analog VU meters, of course)? That would make much more sense to me than the somewhat puzzling comeback of vinyl.

Instead of adapting an existing Internet Radio project to my needs (like support for air traffic control stations), I decided that it would be easier to write my own sketch from scratch. I’m satisfied with the first results, and I learned a lot during this project.

Keypad controlled prototype in radio mode (left) and ATC mode (right)

The radio runs without problems on a Wemos D1 R2, driving an Adafruit VS1053 breakout and a 2.4″ ili9341 TFT display. It can be controlled with a 16-key matrix keypad (the pictures show a Wemos D1 Mini Pro, but its wifi turned out to be too slow for some stations).

The prototype uses almost 500 lines of code for the radio. David Bird’s excellent METAR functions take yet another 500 lines. Too big to post on this page, I’m afraid…

It has the following features (more will be added later):

• Can play mp3 encoded streams from internet radio stations (up to 320 Kbps).
• Built in webserver accepts control commands via a browser.
• Can also be controlled with a 4×4 matrix keypad, using VS1053’s own GPIO pins.
• Offers storage of 40 station presets (grouped in four  bands).
• Displays station name and song title on TFT display and web page.
• Displays a decoded weather report (METAR) when playing an air traffic control (ATC) channel. The first 10 stations in the preset list are reserved for ATC stations (I used David Bird’s excellent functions for METAR decoding).
• A 30 Kbyte ring buffer is used for smooth playback.
• Can play stations with redirected urls.
• Designed to handle chunked transfer encoded streams if necessary (I was unable to test this, because I couldn’t find any station that uses this encoding).
• Stereo dB levels can be read directly from the chip and be used to drive VU meters from PWM pins (or DACs on ESP32).

Below is a flow chart of the initial connection, followed by the streaming process (basically a finite state machine). In practice, it all comes down to determining each incoming byte’s function within the stream by keeping track of some counters and states. Once the actual streaming has started, an incoming byte can be one of the next types:

1. audio byte – will be sent to a ringbuffer that feeds the VS1053 decoder
2. metadata byte – a human readable character from the song title
3. metadata size – an integer; multiplied by 16, it is the following song title’s length
4. CR or LF – used as separators
5. chunk size (if station uses chunked transfer encoding) – size of the next chunk

While still in an early stage of research for my Internet Radio (previous post), I came across Ed Smallenburg’s comprehensive Esp-radio project on github. It’s a very well documented project with a heavily commented sketch.

Instead of proceeding with my own (basic) Internet radio project, I decided to take Ed’s nearly flawless Esp-radio as a starting point, and adapt it according to my personal needs. Most important change will be the addition of two small oled displays for emulating analog VU meters.

There’s also an (even better?) version for ESP32 by the same author. This persuaded me to finally enter the ESP32 world, so now I’m the proud owner of a Wemos LOLIN32 Pro. My hope is that this powerful dual core board will be able to drive the entire setup of radio, TFT touch display, IR remote and VU meter oleds.

Update:

Unfortunately, my Wemos LOLIN32 Pro is from a batch with a faulty serial chip (CP2104). Most of the time, my PC will not recognize the board when I connect it, resulting in the serial chip becoming very hot within 5 seconds. This is my fourth Wemos device, two of which were crap!

However, when the board is recognized, it works fine and I even managed to upload and run the ESP32-Radio sketch. As for performance, I would say that both versions (ESP8266 and ESP32) seem equally satisfying and stable.

Below is a screenshot of the web interface. I removed and changed some buttons from the original version, and added a “now playing” display that updates every two seconds.

My futher plans with an ESP32 based Internet radio will have to wait for the replacement of my board. Planned changes are mainly peripheral and cosmetic, like adding VU-meters and a frequency analyzer. To be continued (stay tuned…)