Sming ESP8266 – Driving a 1.8 TFT ST7735 chip based display

The ST7735 display controller is one of the available display drivers found driving the 1.8 TFT 128×160 resolution display. This driver/TFT combo is found from several sources like Adafruit and eBay, and has software drivers for Arduino and other platforms.
Still these displays, despite the same name (1.8 TFT 128×160), can come with different controllers from the ST7735 chip, like the Samsung S6D02A1 normally found on displays labelled QDTech, and apparently, there are also versions based on the ILI9163C chip.

Anyway I only have one of these displays and it’s based on the ST7735 chip and so here’s how I’ve connected and used a 1.8 TFT with 128×160 resolution the ESP8266 based ESP-12 board using the Sming Framework. The board needs to be an ESP-12 or other that exposes the ESP8266 SPI hardware pins, and so the ESP-01 is out of the question.

Why Sming framework?
The main reason is that I can use Netbeans on my ESP8266 software build process without touching the Arduino IDE… Reason enough, I think 🙂

The Adafruit ST7735 library
The latest Adafruit ST7735 Library supports the Arduino Boards and Teensy boards, and at compile time, specific code segments are enabled/disabled based on the target architecture. For example, when compiling to an Arduino the __AVR__ compiler time variable is defined. As far as I’m aware, this variable is also set when using the Arduino IDE when targeting the ESP8266 board, so no issues here.

The Sming framework defines the following compile time variable: __ESP8266_EX__, and we can just hack the library to support the Sming framework, or adapt it to be used on all or platforms. Anyway, my version is available here, and as far as my tests go, it works fine: Sming Adafruit ST7735 ESP8266.

The hardware connections:
The Library for the Sming framework uses the hardware SPI pins, so the connections should be the following:

Fixed pins SPI pins (can’t be changed)

  1. D13 – Serial data out -> MOSI/SDA
  2. D14 – Clock

Pins that can be changed and defined on the library constructor:

  1. D4 – CS -> Chip Select
  2. D5 – DC -> Data/Command

Also there is the reset pin from the display, that we can connect to an ESP8266 pin, like RST, for example, but I’ve just connected the pin to VCC (3.3v).

Power

The display is powered up by 3.3V. To do that I needed to put a bit of solder on the back pads near the power regulator, that regulates VCC from 5V to 3.3V so that the regulator is out of the circuit. This is of course because the ESP8266 works at 3.3V, so no need for level conversion and other power source.

Software:

Based on this, and using my ST7735 library on Github, my initialization code looks like:

#include <SmingCore/SmingCore.h>
#include <Adafruit_ST7735.h>
#define TFT_CS    4
#define TFT_DC    5

Adafruit_ST7735 tft = Adafruit_ST7735(TFT_CS, TFT_DC, 0);

...
// And on a main function after boot:
void startMain() {

    Serial.println("----TFT_INIT-----");
    tft.initR(INITR_BLACKTAB);
    Serial.println("TFT Initialized");

    tft.setRotation(1);
    tft.fillScreen(ST7735_BLACK);  
       
    tft.drawLine(160, 12, 0, 12, ST7735_YELLOW);    
    cycle.initializeMs(2000, doScreen).start();
}

And that’s it.

Note: Notice that the ST7735 available examples, use extensively the delay function, and that will make the ESP8266 to reboot.

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