Explore LVGL on NuttX RTOS - Rotary Encode Demo

Introduction

This tutorial will explain how you can develop a simple application with Apache NuttX RTOS and the LVGL graphics library. But first, let me show you the board we'll be using.,

The ESP322432S028 board is based on the ESP32 Wrover SoC, built from SunStore. This low-cost development board aims to create graphical applications such as stream desks, analyze charts, visualize data sensors, etc. Additionally, this board has a low-cost built-in RGB LED, SD card slot, GPIO connections, LDR, and speaker output.

Our application will demonstrate how to use a rotary encode to control the value of the gauge and show the current percent.

Before we start, follow these steps to set up your machine.

Hands-on

First, let's understand what a quadrature encoder is (Figure 2) it's an encoder with two output channels, one of which is offset by 90 degrees electrical signal or a quarter cycle. The allowed out-of-phase signal identifies the direction in which the shaft is rotating (clockwise or counterclockwise).

Looking more closely you notice this model has five pins:

• +: positive voltage
• GND: negative voltage
• SW: switch output
• DT/CLK: signal output

Notice on the back of the board that you should find something similar to Figure 3. We will use the connector labeled CN1. The connection with the encode will be disposed of like this:

• + to 3.3V
• GND to GND
• DT to GPIO 22
• CLK to GPIO 27

It's important to inform you that, you may need a JST connector 4 vias.

Schematic

The schematic should follow the connection below (Figure 3):

Configuring NuttX

Download NuttX and Apps

$ mkdir nuttxspace
$ cd nuttxspace
$ cd git clone https://github.com/apache/nuttx
$ cd git clone https://github.com/apache/nuttx-apps apps

Download the App and create a copy into apps/examples

$ git clone git@github.com:halyssonJr/NuttX-Tutorial.git
$ ls
apps    nuttx    NuttX-Tutorial
$ cd NuttX-Tutorial/
$ cp -R lvgl_encoder ../apps/examples

Select the board configuration

$ cd nuttx
$ make distclean
$ ./tools/configure.sh esp32-2432S028:lvgl
$ make menuconfig

Enable the Quadrature Encoder Peripheral

System Type --->

ESP32 Peripheral Selection --->

[*] Pulse Counter (PCNT / QE) Module

• Exit and move down to "Pulse Counter (PCNT) Configuration" :

• Select "Enable PCNT Unit 0" and setup as below:

Enable the Generic Quadrature Encoder Driver

Device Drivers --->

[*] Sensors Driver Support --->

[*] Qencoder

Enable the Demo

Application Configuration --->

Examples --->

[*] LVGL Encoder demo

After setup, go back to the main menu and save the configuration.

Compile and Flash

$ make bootloader
$ make -j8
$ make download ESPTOOL_PORT=/dev/ttyUSB0 ESTOOL_BINDIR=.

Once this part is complete, let's interact with NSH to start the application, you can use picocom, minicom, or another software for your preference. Type ? to access the help commands and built-in apps. You will see three applications available (nsh, sh, and lvencon). To run our application type: lvencon

$ picocom -b 115200 /dev/ttyUSB0

NuttShell (NSH) NuttX-12.4.0
nsh> ?
help usage:  help [-v] [<cmd>]

    .           cp          exit        mkdir       rmdir       umount      
    [           cmp         expr        mkrd        set         unset       
    ?           dirname     false       mount       sleep       uptime      
    alias       dd          fdinfo      mv          source      usleep      
    unalias     df          free        pidof       test        xd          
    basename    dmesg       help        printf      time        
    break       echo        hexdump     ps          true        
    cat         env         kill        pwd         truncate    
    cd          exec        ls          rm          uname       

Builtin Apps:
    lvencon    nsh        sh         
nsh> lvencon
Arc value = 0

Now, we can play with our application. Have fun!