Laser usage counter

Introduction

This project is a counter to monitor usage of a CO2 laser. The principle is to count time when the laser is firing, but not when the head is just moving around.

Monitoring laser activity

Laser is controlled by a 5V TTL signal at 1 kHz PWM modulated. We use a button library and its intrinsic debouncing algorithm to know if the laser is firing or not, without being bothered by low PWM duty cycles (it's stable even with a PWM duty cycle of 0.5%).

There is a little trick: the debouncing algorithm considers the button as released as soon as the input indicates it, but it considers it's a valid press only if pressed continuously for 50 ms. And physical buttons are pulled up by a resistor and connected to ground when pressed. So we will keep that logic for the laser PWM: it will constantly be seen as pressed (=off) but as soon as a PWM pulse is seen, it will be considered as released (=firing) and will return to pressed state only if the PWM has completely stopped for the last 50 ms. We add to the laser "button" an internal pull-down when we declare it as ESP32 is featuring pull-downs, so the counter is stopped when there is no input connected.

Timers

Callbacks linked to button pressed/released will pause/resume a timer. The timer will call a callback every second to update the display. When the timer reaches one full minute, its value (in minutes) is written to EEPROM. We don't write more ofter, otherwise it would wear the EEPROM.

Board

Lilygo TTGO T-display

• Screen: 135x240
• http://www.lilygo.cn/prod_view.aspx?Id=1126
• https://f6czv.fr/en/documentation-on-esp32-and-the-ttgo-t-display

It is based on an Espressif 32 aka ESP32, integrating Wi-Fi and Bluetooth.

ESP32 EEPROM

• https://randomnerdtutorials.com/esp32-save-data-permanently-preferences/
• https://espressif-docs.readthedocs-hosted.com/projects/arduino-esp32/en/latest/api/preferences.html

T-display External flash

• W25Q32 (32M-bit)

GPIO 5V tolerant?

We connect directly the 5V TTL of the Openbuilds BlackBox toolhead PWM pin to pin 27 of the TTGO.

This should be fine as per https://www.letscontrolit.com/forum/viewtopic.php?t=8845

Do not use the 4th pin, it's 0-10V, way too much, unless a resistor divisor is used!

Arduino Board

There are a few TTGO boards in the ESP32 platforms but not the T-display, neither in Arduino IDE nor in Platform.io. See

• https://github.com/Xinyuan-LilyGO/TTGO-T-Display#quick-start
• platformio/platform-espressif32#209
• Xinyuan-LilyGO/TTGO-T-Display#61

Current conclusions are

Board (4Mb flash version):

• Arduino-cli: --fqbn esp32:esp32:esp32:PSRAM=disabled,FlashSize=4M
• Platform.io: platform = espressif32, board = esp32dev

note: If you use Linux, don't forget to give permission for communication with USB.

Libraries

TFT_eSPI

Lilygo provides a configured fork of TFT_eSPI in its TTGO-T-Display repository. It corresponds to the following commit of the official Bodmer/TFT_eSPI and the following configuration in User_Setup_Select.h:

-#include <User_Setup.h>           // Default setup is root library folder
+// #include <User_Setup.h>           // Default setup is root library folder
...
-//#include <User_Setups/Setup25_TTGO_T_Display.h>    // Setup file for ESP32 and TTGO T-Display ST7789V SPI bus TFT
+#include <User_Setups/Setup25_TTGO_T_Display.h>    // Setup file for ESP32 and TTGO T-Display ST7789V SPI bus TFT

We will use latest official Bodmer/TFT_eSPI with TTGO T-display settings from User_Setups/Setup25_TTGO_T_Display.h declared via compilation flags, so we don't need to touch the library files and we follow the same method as this platformio.ini example.

Button2

Lilygo provides files of Button2 in TFT_eSPI/examples/FactoryTest in its TTGO-T-Display repository. It corresponds to v1.0 of the official LennartHennigs/Button2.

We will use latest official LennartHennigs/Button2.

TickTwo

We will use sstaub/TickTwo to control the timer, as it provides convenient functions for ESP32 to suspend/resume the timer and call callbacks at predefined intervals.

includes

TFT_eSPI includes the Adafruit_GFX but for easy use, we include the Free_Fonts.h which defines short names for the fonts.

Arduino-cli

Prerequisites

$ ./arduino-cli-0setup

Compilation and flashing

$ ./arduino-cli-compile
$ ./arduino-cli-upload

Platform.io

Prerequisites

Everything needed is defined in ./platformio.ini

See https://docs.platformio.org/en/latest/platforms/espressif32.html for details.

Compilation and flashing

source ~/.platformio/penv/bin/activate
pio run
pio run --target upload
deactivate

Help wanted

It could be cool to make a nice case. like this one:

check this issue for more details: #1

Issues

• Does not boot properly when powered via 5V pin, until reset by button.
• TODO: Platformio settings: set proper flash size (default is 4Mb, should be possible to set 16Mb with board_upload.flash_size = 16MB and board_upload.maximum_size = 16777216)