Pseudostatic Ram (PSRAM)

 

Just got me a second LOLIN D32 Pro v.2, this time with the newer ESP32-WROVER-B module on board. For just € 1,- extra, it has 4x more RAM and 2x more PSRAM. But what is this PSRAM, and could I use it for memory-hungry sketches, like the ones where AI or pathfinding algorithms are involved?

Searching the Internet gave me a first idea of what it is, but more important: I found out how to use it, which luckily turned out to be remarkably simple.

Below is a simple demo sketch that shows how to address PSRAM. It allocates a 1 MB buffer in PSRAM and then starts writing random integers at random positions, reading them back again for control. Make sure that PSRAM is enabled when you compile it, otherwise the ESP32 will panic! (it’s an option in the Tools menu of the Arduino IDE after a WROVER based ESP32 board has been selected).

Note that GPIO pins 16 and 17 are used for communication between ESP32 and PSRAM, so WROVER-based boards will not have these pins broken out.

Also note that content in PSRAM will be lost after the ESP32 loses power (still have to figure out what happens during deep sleep).

My search for information on PSRAM triggered a more general interest in the chip’s architecture. Espressif’s documentation has been very helpful.

 

Swinging Needles

…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.

Mini MP3 Player

This little €4 module filled my entire weekend, mainly spent on finding the right documentation and a library that will work on Arduino, ESP8266 and ESP32. It’s a DFPlayer Mini MP3 Player from DFRobot (or, more likely, one of its many clones).

It can play MP3 and WAV files, stored on an SD card in the onboard card reader or from an attached USB drive. So far, I only tested MP3 files from SD.

You can connect one (4 Ω) speaker to the (quite impressive) onboard mono amplifier. Stereo line output is said to be provided on the DAC_R and DAC_L pins.

The main control method of this player is via commands over the module’s 9600 baud serial port. A subset of most commonly used commands can also be executed by means of two GPIO pins and/or two resistor-sensitive ‘ADKEY’ pins.

I made a false start by testing it on an ESP32 over hardware serial. That didn’t seem to work, so I tried an ESP8266 over software serial. That didn’t work either, and I had reached the point of giving up, assuming it was just another Chinese fake, when I gave it one more try on my good old Arduino Uno. With a quick & dirty 1K resistor for level shifting the module’s RX pin, the example sketch of one of many libraries finally made the little guy play me a song! In the end, it was the power supply that made the difference.

Some important things that I learned so far:

  • The module works best when powered by a stable 5 Volt. My Arduino Uno and Wemos D1 R2 could deliver it from their 5V pin, smaller ESP8266 and ESP32 boards couldn’t. In that case: use a separate 5 Volt power supply.
  • Wiring as suggested here caused a shutdown of my laptop’s usb port! I’m still searching for a way to connect the module to ESP32.
  • The module operates on 3.3 V logic level, so make sure to level shift the connection to the module’s RX pin when using a 5 V microcontoller.
  • Startup noise disappeared after I connected both GND pins from the player to ground.
  • Although it’s for a Flyron FN-M16P module, this excellent manual/datasheet has more and better written information than DFRobot’s own summary. Apparently both modules use the same commands and probably have the same chip.
  • Getting stereo ouput from the DAC pins is still a problem. According to the manual, DAC is enabled on startup, but is it? Explicitely enabling it by sending 0x0000 to memory address 0x1A made no difference while sending 0x0001 instead (supposed to turn it off) started a terrible noise…
  • I tested quite some libraries from github, most of which have issues [update: starting sketches with delay(1000); solved most of them] and seem unnecessarily complicated to me. An exception is this simple and transparent library that is basically just a wrapper for sending serial commands. It can easily be extended with additional methods, even by unexperienced C++ programmers. You just have to lookup the command- and parameter bytes for the desired function in the datasheet and create a new function to send them (see example at the bottom of this page). [update: the author of the library has meanwhile added more commands]
  • The module has an SPK_1 and an SPK_2 pin, with a GND pin in between, which could suggest that it has a stereo amplifier. Although the documentation clearly says it’s mono, someone actually published a wiring diagram with two speakers connected. This person may own a different version of the module, but mine definitely has a mono amplifier. So the two wires of a single speaker should go to the SPK pins.

[ Wiring for Arduino Uno, with SoftSerial on pins 10 and 11; don’t forget the 1K resistor! ]

 

The location of files and their names is also very important because of the way commands address them. All information can be found in the datasheet, but here’s a summary:

  • The SD card’s maximum size is 32 GB. It must be FAT or FAT32 formatted.
  • There can be up to 3000 .mp3 (or .wav) files in the root directory of the SD card, named 0001.mp3 to 3000.mp3.
  • The root can have up to 99 subdirectories, named 01, 02, … 99. Each of these subdirectories can hold up to 255 files. Their names must start with 001, 002, … 255,  but you can append decriptive titles to these files, e.g. 007_James_Bond_Tune.mp3.
  • You can have a special subdirectory in the root named MP3. This can hold up to 3000 files, named 0001.mp3 to 3000.mp3.
  • You can also have a subdirecory ADVERT in the root. Special commands are available for making tracks in this folder interrupt currently playing tracks from the MP3 folder (for advertisement puposes). The rules for the MP3 subdirectory apply here as well.
  • Don’t create subdirectories inside subdirectories.
  • The module does not actually use file- or directory names, but the order of files and directories in the SD card’s FAT. The previously mentioned naming conventions just try to give you control over that order. If you properly organize your audio files in a folder on your PC first, and then copy that entire structure to a freshly formatted SD card, then (in theory) the FAT order should match the file- and directory numbering. See also this tool

Apart from adding some extra functions to the above mentioned library, I still have to find out how to reliably receive and read the module’s response to commands and queries. Once that I’m in full control over this (for its price) remarkably versatile module, it will be useful for a couple of ‘talking’ projects that I have in mind. Probably just mono and not ESP32 driven, but anyway: lots of fun for just €4.

 


Here’s an example of a function that I added to the DFPlayerMini_Fast library. Calling play_in_dir(2, 5) will play file 005.mp3 in subdirectory 02.

Using an existing function as a template, I first added my new function to the DFPlayerMini_Fast.cpp file:

Then I added these two accompanying lines to the DFPlayerMini_Fast.h header file:

and (inside the code for the class):

 

Explanation: according to the datasheet, the 10 (hexadecimal) bytes that have to be sent (by the sendData() function) to play track 005.mp3  in directory 02 are:

7E FF 06 0F 00 02 05 xx xx EF

7E FF 06 are the first three bytes for every command. The following 0F is de code for ‘play a file in a direcory’, the following 00 means ‘no confirmation feedback needed’ and is followed by the two parameters for the desired directory- and file number: 02 and 05. Then comes xx xx which are two checksum bytes that will be calculated and replaced by the findChecksum() function of the library before the command is sent by sendData(). Finally, every command has to be closed by EF.

As you can see, my newly added function play_in_dir() takes two parameters only, corresponding with two bytes in the command sequence. All other bytes of the sequence are either fixed or calculated by the findChecksum() function.

 

 

Dual Core Business

Almost a year after finishing my ESP8266-based Internet Radio project, I still have had no idea why running that sketch on the much more powerful ESP32 produces a heavily stuttering sound, resembling Michael Palin in “A Fish Called Wanda”.  So I wondered if I could solve this problem by dividing the audio streaming process between the ESP32’s two cores: filling the audio buffer on one core, and feeding the VS1053 decoder from that buffer on the other core.

Thanks to its builtin FreeRTOS, pinning a task to a specific core of the ESP32 is easy:

1. Put the code for the task in a function, wrapped in an endless for (;;) { } loop.

2. Create a task handle for the task in the main section of the sketch:

3. Create the task, specifying which function it should execute on which core:

 

(Since there was nothing in my loop() function (yet), I put a delay(1000); command in it. The loop() function runs on core 1, and I didn’t want it to claim too much of that core’s processor time.)

So my Radio sketch will have two independent tasks running on different cores: one that listens to the radio station’s audio stream for filling the circular buffer, and one for feeding the VS1053 decoder with bytes from that buffer. Both processes maintain their own pointer for accessing the circular buffer and the code guarantees that they will never catch up with the other process’ pointer. So there is no need to use a semaphore.

However, my first step into the dual core business produced an error. A ‘watchdog timer’ had become nervous and halted the ESP32. It turned out that including the following line in both functions solved at least that problem (bug?):

 

Now the ESP32 no longer crashed, and it actually produced sound. But alas, it was Michael Palin again…!

I can’t think of any reason for this behaviour. The serial monitor shows that the ESP32 has no problem filling the 30 Kbyte circular buffer, so feeding the VS1053 seems to be the bottleneck. I swapped cores for both tasks, but that didn’t help.

UPDATE: Meanwhile, I had become so desperate about finding a solution that I renamed the project “dESPeRadio“. But then, during a sleepless night, I wondered if the ESP32 might perhaps need a different policy for filling the circular buffer. The chunks it reads from the WiFi client per loop cycle have an upper size limit of 1024 bytes, in order to prevent the VS1053 from running dry during the process. But I didn’t specify a lower size limit.

For the ESP8266 this was OK, but the EP32 is so fast that, after it has rapidly filled the circular buffer, there will never be more than just a couple of free positions in the next loop cycle. All following cycles will therefore be very inefficient, causing so much overhead that the VS1053 actually runs dry in a very regular time pattern – the stuttering.

So I added just one single line for skipping the fill cycle if there’s less than 512 bytes of free buffer space available and uploaded the sketch without much hope, because so many ‘good’ ideas had failed before. What followed was complete silence…, which then turned out to be the pause between two movements of  Brahms’ fourth symphony! Then the music started in clean and, above all, uninterrupted sound!

The radio has been running non-stop now for a couple of hours. It looks like I finally have a solid and stable foundation for further development of my dESPeRadio on ESP32. Although using two cores isn’t necessary, it will be nice way to explore FreeRTOS.

In order to keep the code clean and readable, all future features and controls will be implemented as (optional) includible header files. I’ll make the full code available in my first github repository soon, so if you’re interested, stay tuned.

Plans for additional control options, apart from the already implemented keypad, are:

  • ☑ an embedded web server
  • ☐ the touch screen overlay of my display
  • ☐ IR remote
  • ☐ rotary encoders for volume, bass and treble

Other plans:

  • ☑ add VU meters (I love the analogue ones!)
  • ☐ use a FreeRTOS queue instead of a circular buffer

 

 

 

 

 

LOLIN TFT-2.4 Shield

Here’s a well designed new display from Wemos Electronics. They call it a (D1 Mini) Shield, but instead of going on top of a Wemos D1 Mini (Pro), it lets you plug in the Mini at the back of the 2.4″ TFT touch screen display, leaving all GPIO pins accessible, thanks to double header rows. Very useful!

This table shows the internal pin mapping when used as a shield. For TFT_LED, TFT_RST and TS_CS, this mapping can be changed by closing solder bridges at the back of the display.

The default pin mapping leaves I2C pins D1 and D2, as well as D4, A0, TX and RX available for other purposes. With my Wemos Mini Pro v2 plugged in, this shield has become my first choice for battery powered esp8266 projects that require a display.

 

 

 

But there’s more. All pins are also broken out to a breadboard-friendly header and to a TFT connector. Connecting the display to a D32 Pro (that has the same TFT connector) now requires only one (special) cable! The picture shows the connector’s pinout.

 

The 320×240 display uses the well-proven ili9341 chip, for which I already wrote a lot of sketches, both for esp8266 and esp32 boards. The XPT2046 library can be used to drive the touch screen.

I tested several sketches on a plugged-in Mini Pro, as well as a TFT cable-connected D32 Pro, and everything worked fine. Example sketches on the Wemos site use Adafruit’s ili9341 library, but I prefer the much faster TFT_eSPI library.

This is a well-thought product that makes wiring very convenient and stable. Recommended!

 

 

Quest for Fire

By no means a gamer myself, I’ve always been interested in the math behind the graphics in video games. A previous post showed how simple clouds can be produced by the Diamond-Square algorithm, running on an esp8266. That algorithm can generate maps and landscapes as well.

Another visual effect on my todo list was algorithmically simulated fire.

 

The video shows my first attempt on a small TFT display. I had to write a relatively simple algorithm, because it needs to run on a microcontroller. Some further experimenting with the color palette, weighting factors and randomization, as well as adding Perlin noise, will hopefully result in a more realistic fire. I also plan to add a rotary encoder for regulating the ‘fire’.

 

Visual memory

Soon after my start with Arduino, I bought an external 32KB EEPROM, just in case a future project would need more memory than the board’s modest SRAM. But when I finally needed it for a sketch, I realized that the 300 KByte RAM of my 480×320 TFT display could be used for this purpose as well.

I had used pixels as memory before in visualisations of IFS fractals, where I made each pixel keep track of the number of times it was ‘hit’ by the iteration process, and then color it accordingly. Recent examples are this autumn inspired version of Barnsley’s Fern and this conifer-like fractal, based on an example on Ken Brakke’s IFS page. Both fractals were produced by an esp8266 on a 320×240 TFT display (ili9341).

Using a display as external memory for projects brings memory intensive algorithms, like the A* path search algorithm for my 15-Puzzle project, within reach of Arduino and ESP boards. The only prerequisite is that your display library lets you read single pixel values. Bonus: leaving the display’s backlight on will show a ‘brain scan’ of the sketch in progress.

 

ESP32 – mixed feelings

 My ESP32 boards: LOLIN32 Pro, LOLIN32 Lite, LOLIN D32 and LOLIN D32 PRO 

After a false start with ESP32 (my LOLIN32 Pro had an overheating CP2102 chip*), I’m gradually becoming more familiar with ESP8266’s big brother. However, experience with 4 different boards (all with rev. 1 chips) still leaves me with mixed feelings. My personal balance so far:

Pros:

  • The specs and features are impressive, especially given its low price
  • Control over its two cores via FreeRTOS works great
  • It has a fair number of GPIOs (unlike the ESP8266)
  • Sketches run very fast. Great for my fractal sketches!
  • No longer needs yield() commands to prevent it from crashing

Cons:

  • It’s sensitive to solderless wiring (probably because of its high bus speeds)
  • The 4 different boards I tried all had problems feeding power-hungry peripherals
  • I’m experiencing some unexplicable issues, especially when driving TFT displays

Tips for troubleshooting:

  • Provide your ESP32 with enough power. Some USB outlets will not deliver enough juice, especially not through low quality USB cables
  • Use an external power supply for power-hungry connected devices, otherwise (at least) SPI may become unstable
  • Consider using contact spray for unstable solderless projects
  • Don’t use heavily used breadboards
  • Never use a hammer (though working with ESP32 can be frustrating…)

So will my ESP8266 boards start gathering dust from now on? Certainly not before I manage to run a turbo version of my beloved What’s Up sketch on the ESP32. I just can’t wait to watch those plane icons slide more smoothly over the map. Bodmer’s TFT_eSPI library offers enough speed for that, but I keep having issues with it when used in the What’s Up sketch on ESP32.

* The issue was reportedly caused by a design flaw. After I had received a LOLIN32 Lite for replacement, I discovered that using a longer USB cable (2+ meter) fixed the problem!

Newton fractal

Here’s another famous fractal that I wanted to try on Arduino: the Newton fractal. It’s named after Isaac Newton’s iterative method for finding roots of functions. The classic example applies the method to function f(z) = z3 – 1 , where z is a complex number. This function has three roots in the complex plane.

classic newton fractal

The sketch that produced this picture loops over the pixels of a 480×320 display, mapping each of them to a complex number z0, that will serve as the initial value for Newton’s iteration process:

zn+1 = zn – f(zn) / f'(zn)

The basic color of a pixel (red, green or blue) depends on to which of the three roots the process converges. Its color intensity depends on the number of iterations that were needed to reach that root within a pre-defined precision. It’s just that simple!

Apart from playing with different color mappings (always essential for producing visually appealing fractals), I wanted to use modified versions of Newton’s method, as well as to apply them to different functions. The Arduino core has no support for complex calculus, and a library that I found didn’t even compile. So I wrote a couple of basic complex functions and put them in a functions.h file. There must better ways, but it works for me.

Once you have a basic sketch, the canvas of complexity is all yours!

 

 

f(z) = z4 – 1

 

This is my functions.h file. It must be in the same folder as the fractal sketch.

 

And here’s the Newton fractal sketch. Note the #include “functions.h” on the first line.

 

 

Small Talk

Two years ago, I used an Emic2 module for a couple of TTS (text-to-speech) projects. Despite its flexibility (someone even made it sing Bohemian Rhapsody here), the Emic2 sounds quite ‘robotic’ when used for direct TTS conversion. Not the best choice for a Talking Alarm Clock project, unless you like to wake up next to Stephen Hawking… (no offense).

So I considered to compose full sentences out of spoken language fragments, stored in mp3 format on my VS1053 breakout’s SD card. Then I discovered this google_tts library on github. It takes a text string as input and returns a link to a correspondig mp3 file in the Google cloud. You can specify one out of 30 languages, as well as a voice (both male and female).

I tried it, and the result is fully satisfying. The sketch starts with retrieving the local time for my location, provided by a simple api on my server. Then it fills a string variable with a natural language sentence like “The current time is <hr> hour and <min> minutes” (in Dutch in my sketch). Next, this string is processed by the library and the resulting link is sent to translate.google.com. The returned mp3 data is streamed to the VS1053 chip and sent as analogue audio to the amplifier.

This project is definitely going to replace my alarm clock. From now on, a soft female voice will wake me up in the morning, reading the current time and weather forecast, before telling me to stay in bed for a while. So glad I didn’t use the Emic2…

Here’s a basic sketch (current time only). You can ignore warnings when compiling it for esp32: it’ll run just fine on esp32 boards.