Arduino with DHT11 Sensor and ST7789 TFT Display


This post shows how to interface Arduino UNO board with DHT11 (RHT01) digital humidity and temperature sensor.
The Arduino reads temperature (in °C) & humidity (in rH%) values from the DHT11 sensor and print their values 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.

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

About DHT11 sensor:
There are two types of the DHT11 sensor: old type (AOSONG) and new type (ASAIR). The differences between the 2 types are summarized below:

Seeed Studio provides a good module of the new DHT11 sensor (ASAIR version) named “Grove Temperature & Humidity Sensor”, more details in its official page:
Grove Temperature & Humidity Sensor

Hardware Required:

  • Arduino board
  • ST7789 TFT display module (1.3″, 1.54″ …)
  • DHT11 (RHT01) humidity and temperature sensor   —->  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)
  • 4.7k ohm resistor
  • Breadboard
  • Jumper wires

Arduino with DHT11 sensor and ST7789 TFT display circuit:

The image below shows project circuit diagram.

The DHT11 sensor has 4 pins (from left to right):
Pin 1 is power supply pin, connected Arduino 5V pin,
Pin 2: data output pin, connected to Arduino analog pin 2 (A2),
Pin 3: not connected pin,
Pin 4: GND (ground), connected to Arduino GND pin.

A pull-up resistor of 4.7k ohm is required because the DHT11 sensor has an open drain output.

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).

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).

Arduino with DHT11 sensor and ST7789 TFT display 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 DHT11 sensor, it may be installed using library manager (in the search box write “dht” 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 DHT 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.

The 3 libraries are included in the main code as follows:


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