Interfacing Arduino with DS3231 RTC and ST7789 TFT

This tutorial shows how to make a digital real time clock using Arduino UNO and DS3231 RTC module where time & date can be set with two push buttons connected to the Arduino board and they are printed (with RTC chip temperature) on ST7789 TFT display.

The ST7789 TFT module contains a display controller with the same name: ST7789. It’s a color display that uses SPI interface protocol and requires 3, 4 or 5 control pins, it’s low cost and easy to use. This display is an IPS display, it comes in different sizes (1.3″, 1.54″ …) but all of them should have the same resolution of 240×240 pixel, this means it has 57600 pixels. This module works with 3.3V only and it doesn’t support 5V (not 5V tolerant).

TFT: Thin-Film Transistor.
SPI: Serial Peripheral Interface.
IPS: In-Plane Switching.
IIC (or I2C): Inter-Integrated Circuit.

To see how to interface Arduino with ST7789 TFT display, visit this post:
Interfacing Arduino with ST7789 TFT Display – Graphics Test Example

Hardware Required:

  • Arduino board
  • ST7789 TFT display module (1.3″, 1.54″ …)
  • DS3231 module   —->  DS3231 datasheet
  • 4 x 3.3k ohm resistor (+1 if the display module has CS pin)
  • 4 x 2.2k ohm resistor (+1 if the display module has CS pin)
  • 2 x push button
  • 3V coin cell battery
  • Breadboard
  • Jumper wires

Interfacing Arduino with DS3231 RTC and ST7789 TFT:
Project circuit schematic diagram is shown below.

The ST7789 display module shown in project circuit diagram has 7 pins: (from right to left): GND (ground), VCC, SCL (serial clock), SDA (serial data), RES (reset), DC (or D/C: data/command) and BLK (back light).
Connecting the BLK pin is optional. The back light turns off when the BLK pin connected to the ground (GND).

Arduino DS3231 RTC ST7789 TFT display

As mentioned above, the ST7789 TFT display controller works with 3.3V only (power supply and control lines). The display module is supplied with 3.3V (between VCC and GND) which comes from the Arduino board.

All Arduino UNO board output pins are 5V, connecting a 5V pin to the ST7789 TFT display may damage its controller.
To connect the Arduino to the display module, I used voltage divider for each line which means there are 4 voltage dividers. Each voltage divider consists of 2.2k and 3.3k resistors, this drops the 5V into 3V which is sufficient.

If the display module has a CS pin (Chip Select) then it should be connected to Arduino digital pin 10 through another voltage divider.

So, the ST7789 TFT display is connected to the Arduino board as follows (each one through voltage divider):
RST pin is connected to Arduino digital pin 8,
DC pin is connected to Arduino digital pin 9,
SDA pin is connected to Arduino digital pin 11,
SCL pin is connected to Arduino digital pin 13.

Other pins are connected as follows:
VCC pin is connected to Arduino 3V3 pin,
GND pin is connected to Arduino GND pin,
BL (LED) pin is connected to Arduino 3V3 pin (optional).

The DS3231 RTC module SDA (serial data) and SCL (serial clock) pins are respectively connected to Arduino A4 and A5 pins (ATmega328P hardware I2C module pins).
The DS3231 RTC chip is supplied with 5V from the Arduino board.

The two push buttons which are connected to Arduino digital pins 6 and 7 are for setting time & date of the clock.

Arduino with DS3231 RTC and ST7789 TFT code:
The following Arduino code requires 3 libraries from Adafruit Industries:
The first library is a driver for the ST7789 TFT display which can be installed from Arduino IDE library manager (Sketch —> Include Library —> Manage Libraries …, in the search box write “st7789” and install the one from Adafruit).

The second library is Adafruit graphics library which can be installed also from Arduino IDE library manager.
The 3rd library is for the DS1307 RTC, it may be installed using library manager (in the search box write “rtclib” and choose the one from Adafruit).

The 3 libraries can be installed manually, first download them from the following 3 links:
Adafruit ST7789 TFT library    —->  direct link
Adafruit graphics library        —->  direct link
Adafruit RTC library              —->  direct link

After the download, go to Arduino IDE —> Sketch —> Include Library —> Add .ZIP Library … and browse for the .zip file (previously downloaded).
The same thing for other library files.

Hints:
The 3 libraries are included ( & Arduino Wire library) in the main code as follows:

The ST7789 TFT module pins (CS, RST and DC) connections are defined as shown below (even the display module has no CS pin but its definition is required by the Adafruit ST7789 library):

The other display pins (SDA and SCL) are connected to Arduino hardware SPI module pins (digital pin 11 and digital pin 13 respectively for MOSI and SCLK).

The Adafruit ST7789 library is initialized with this line:

And the TFT display is initialized using the following command:

The two push buttons are defined in the code as:

Functions used in the code:
bool debounce (): this function is for button B1 debounce, returns 1 if button is debounced.

void RTC_display(): displays day of the week, date and time on the display.

byte edit(byte parameter): this function is for setting the real time clock, returns the edited parameter.

Rest of code is described through comments.

Full Arduino code:

Arduino with ST7789 color TFT display and DS3231 RTCC module

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