Turn an ESP32 into a Browser Oscilloscope

ESP32 Oscilloscope with Web User Interface

Demo ESP32 oscilloscope:

• http://jurca.dyn.ts.si/oscilloscope.html

• https://jurca.dyn.ts.si/oscilloscope.html

The latest changes

The latest release works more smoothly, is more stable, and provides an improved user experience — especially on smartphones.

It no longer includes the HTTP server directly. It now depends on the separate Arduino library ESP32_Multitasking_Network_Suite.

You can install the library through the Arduino IDE or download it from GitHub:

• ESP32_Multitasking_Network_Suite
  https://github.com/BojanJurca/Multitasking-Http-Ftp-Telnet-Ntp-Smtp-Servers-and-clients-for-ESP32-Arduino-Library

  • ThreadSafeFS
    https://github.com/BojanJurca/Thread-safe-file-sytem-wrapper-Arduino-library-for-ESP32

  • LightweightSTL
    https://github.com/BojanJurca/Lightweight-Standard-Template-Library-STL-for-Arduino

• WolfSSL (if HTTPS server is beeing used)
  https://github.com/wolfSSL/Arduino-wolfSSL

About the ESP32 oscilloscope

Esp32 oscilloscope takes up to 736 samples per screen but the sampling rate may not be completely constant all the time since there are other processes, (beside the sampling process itself, especially if you are using Esp32 oscilloscope as a part of other projects) running at the same time. ESP32 may also not always be able to keep up with the desired sampling frequency.

Esp32 oscilloscope displays the samples as they are taken which may not be exatly the signal as it is on its input GPIO. The samples are represented by digital values 0 and 1 or analog values from 0 to 4095 which corresponds to 0 V to 3.3 V.

You are welcome to modify oscilloscope.html to match your needs, meaning, specify which GPIOs are actually used as digital inputs and which as analog inputs, to make some sense of what signals you are about to monitor.

ESP32 oscilloscope was first meant to be just a demonstration of the Multitasking-Esp32-HTTP-FTP-Telnet-servers-for-Arduino (https://github.com/BojanJurca/Multitasking-Esp32-HTTP-FTP-Telnet-servers-for-Arduino) capabilities and is still fully included there, but it seems to be better off on its own. Only functionalities necessary for an oscilloscope to work are used here.

Setup instructions

1. Copy all files in this package to the Esp32_oscilloscope directory.

2. Open Esp32_oscilloscope.ino with Arduino IDE.

3. Find and change YOUR-STA-SSID to your WiFi SSID and YOUR-STA-PASSWORD in Esp32_servers_config.h file to your WiFi SSID and password.

4. Oscilloscope uses LittleFS file system so select one of SPIFFS partition schemas (Tools | Partition scheme | ...).

Some ESP32 boards do not have a flash disk. In this case just comment out the line #define FILE_SYSTEM FILE_SYSTEM_LITTLEFS and ESP32 oscilloscope will use progmem instead of the file system to store the oscilloscope.html file.

1. Compile the sketch and run it on your ESP32 for the first time. Doing this, ESP32 flash disk will be formatted with the LittleFS file system. WARNING: every information you have stored into ESP32s flash memory will be lost.

2. FTP to your ESP32 (By using ftp command line utility or Windows explorer. User name and password are not required) and upload the following files to /var/www/html directory:

• android-192-osc.png,
• apple-180-osc.png,
• oscilloscope.html.

C:\esp32_oscilloscope>ftp YOUR-ESP32-IP
Connected to 10.0.0.3.
220-ESP32 FTP server - everyone is allowed to login
User (10.0.0.3:(none)):
331 enter password
Password:
230 logged on, use "/" to refer to your home directory "/"
ftp> put android-192-osc.png /var/www/html/android-192.png
226 /var/www/html/android-192-osc.png transfer complete
ftp> put apple-180-osc.png /var/www/html/apple-180.png
226 /var/www/html/apple-180-osc.png transfer complete
ftp> put oscilloscope.html /var/www/html/oscilloscope.html
226 /var/www/html/oscilloscope.html transfer complete
ftp>

1. Open http://YOUR-ESP32-IP/oscilloscope.html with your browser.

2. If you're getting inverse analog signals, as it happens on some of ESP32 boards, comment or uncomment compiler directives INVERT_ADC1_GET_RAW and/or INVERT_I2S_READ in oscilloscope.h respectively. If your ESP32 board supports i2s interface (like ESP32 DevKitC, NodeMCU-32S, ...) you can also decide if you want to use it (or not). The benefit of using i2s interface is higher sampling frequency and quality of a single analog signal. The drawback, on the other hand, is that you can not use more than one analog oscilloscope at a time.

Things to consider when analogReading GPIOs

ESP32 has two SARs (Successive Approximation Registers) built-in among which only ADC1 (GPIOs 36, 37, 38, 39, 32, 33, 34, 35 on ESP32 board but other boards (S2, S3, ...) have different GPIOs connected to ADC1) can be used for oscilloscope analogReadings. ADC2 (GPIOs 4, 0, 2, 15, 13, 12, 14, 27, 25, 26 on ESP32 board but other boards (S2, S3, ...) have different GPIOs connected to ADC2) can perform analogReadings only when WiFi is not working. Since oscilloscope uses WiFi, ADC2 GPIOs are not available at this time.