Interfacing Arduino with DHT11 sensor and ST7735 TFT display
Interfacing Arduino with DHT11 sensor and ST7735 TFT display
This post shows how to interface Arduino UNO board with DHT11 digital humidity and temperature sensor.
The Arduino reads temperature (in °C) & humidity (in rH%) values from the DHT11 sensor and print their values on ST7735 TFT display.
The ST7735 TFT used in this project is a color display which has a resolution of 128×160 pixel and it communicates with the master device using SPI (Serial Peripheral Interface) protocol.
To see how to interface Arduino with ST7735 TFT display, visit the following post:
Arduino ST7735 1.8″ TFT display example
And for interfacing Arduino with DHT11 sensor, see the post below:
Arduino interfacing with DHT11 sensor and LCD
Hardware Required:
- Arduino board
- ST7735S (ST7735R) TFT screen
- DHT11 (RHT01) humidity and temperature sensor —-> datasheet
- 5 x 1k ohm resistor
- 4.7k ohm resistor
- Breadboard
- Jumper wires
Interfacing Arduino with ST7735 TFT and DHT11 sensor circuit:
Project circuit diagram is shown below.
The DHT11 sensor has 4 pins (from left to right):
VCC: connected to Arduino 5V pin,
Data pin: connected to Arduino analog pin 0 (A0),
Not connected pin,
GND: connected to Arduino GND pin.
A pull-up resistor of 4.7k ohm is required because the DHT11 sensor output is open drain.
The ST7735S shown in project circuit diagram has 8 pins: (from right to left): RST (reset), CE (chip enable), DC (or D/C: data/command), DIN (data in), CLK (clock), VCC (5V or 3.3V), BL (back light) and Gnd (ground).
Normally the ST7735 display works with 3.3V only, but many boards of this display have a built-in 3.3V regulator (AMS1117 3V3) like the one shown in the circuit diagram. This regulator supplies the display controller with 3.3V from 5V source.
All Arduino UNO board output pins are 5V, connecting a 5V pin directly to the ST7735 display board may damage its controller circuit. To avoid that, I connected each control line of the display to the Arduino board through 1k ohm resistor.
So, the ST7735 display is connected to the Arduino board as follows (each one through 1k resistor):
RST pin is connected to Arduino digital pin 8,
CS pin is connected to Arduino digital pin 9,
D/C pin is connected to Arduino digital pin 10,
DIN pin is connected to Arduino digital pin 11,
CLK pin is connected to Arduino digital pin 13.
Arduino with ST7735 display and DHT11 sensor code:
The following Arduino code requires 3 libraries from Adafruit Industries:
The first library is a driver for the ST7735 TFT display, download link is below:
Adafruit ST7735 display library
The 2nd library is Adafruit graphics library which can be downloaded from the following link
Adafruit graphics library —-> direct link
The 3rd one is for the DHT11 sensor:
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 the other library files.
The previous 3 libraries are included in the main code as follows:
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#include <Adafruit_GFX.h> // include Adafruit graphics library
#include <Adafruit_ST7735.h> // include Adafruit ST7735 TFT library
#include <DHT.h> // include DHT library
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The ST7735 TFT display is connected to Arduino hardware SPI module pins (clock and data), the other pins which are: RST (reset), CS (chip select) and DC (data/command) are defined as shown below:
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#define TFT_RST 8 // TFT RST pin is connected to arduino pin 8
#define TFT_CS 9 // TFT CS pin is connected to arduino pin 9
#define TFT_DC 10 // TFT DC pin is connected to arduino pin 10
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The definition of DHT11 data pin and the initialization of the DHT library:
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#define DHTPIN A0 // DHT11 data pin is connected to Arduino analog pin 0
#define DHTTYPE DHT11 // DHT11 sensor is used
DHT dht11(DHTPIN, DHTTYPE); // initialize DHT library
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Rest of code is described through comments.
Full Arduino code:
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/*
* Arduino interface with ST7735 color TFT (128×160 pixel) display and
* DHT11 digital humidity and temperature sensor.
* This is a free software with NO WARRANTY.
* http://simple-circuit.com/
*/
#include <Adafruit_GFX.h> // include Adafruit graphics library
#include <Adafruit_ST7735.h> // include Adafruit ST7735 TFT library
#include <DHT.h> // include DHT library
#define TFT_RST 8 // TFT RST pin is connected to arduino pin 8
#define TFT_CS 9 // TFT CS pin is connected to arduino pin 9
#define TFT_DC 10 // TFT DC pin is connected to arduino pin 10
// initialize ST7735 TFT library
Adafruit_ST7735 tft = Adafruit_ST7735(TFT_CS, TFT_DC, TFT_RST);
#define DHTPIN A0 // DHT11 data pin is connected to Arduino analog pin 0
#define DHTTYPE DHT11 // DHT11 sensor is used
DHT dht11(DHTPIN, DHTTYPE); // initialize DHT library
void setup(void)
{
tft.initR(INITR_BLACKTAB); // initialize a ST7735S chip, black tab
tft.fillScreen(ST7735_BLACK); // fill screen with black color
tft.drawFastHLine(0, 50, tft.width(), ST7735_BLUE); // draw horizontal blue line at position (0, 50)
tft.drawFastHLine(0, 102, tft.width(), ST7735_BLUE); // draw horizontal blue line at position (0, 102)
tft.setTextColor(ST7735_WHITE, ST7735_BLACK); // set text color to white and black background
tft.setTextSize(1); // text size = 1
tft.setCursor(4, 16); // move cursor to position (4, 16) pixel
tft.print(“ARDUINO + ST7735 TFT”);
tft.setCursor(22, 33); // move cursor to position (22, 33) pixel
tft.print(“+ DHT11 SENSOR”);
tft.setTextColor(ST7735_GREEN, ST7735_BLACK); // set text color to green and black background
tft.setCursor(25, 61); // move cursor to position (25, 61) pixel
tft.print(“TEMPERATURE =”);
tft.setTextColor(ST7735_YELLOW, ST7735_BLACK); // set text color to yellow and black background
tft.setCursor(34, 113); // move cursor to position (34, 113) pixel
tft.print(“HUMIDITY =”);
tft.setTextSize(2); // text size = 2
// initialize DHT11 sensor
dht11.begin();
}
char _buffer[7];
// main loop
void loop()
{
// read humidity
byte humi = dht11.readHumidity();
// read temperature
byte temp = dht11.readTemperature();
// print temperature (in °C)
sprintf(_buffer, “%02u.0”, temp);
tft.setTextColor(ST7735_RED, ST7735_BLACK); // set text color to red and black background
tft.setCursor(29, 78);
tft.print(_buffer);
tft.drawCircle(83, 80, 2, ST7735_RED); // print degree symbol ( ° )
tft.setCursor(89, 78);
tft.print(“C”);
// print humidity (in %)
sprintf(_buffer, “%02u.0 %%”, humi);
tft.setTextColor(ST7735_CYAN, ST7735_BLACK); // set text color to cyan and black background
tft.setCursor(29, 130);
tft.print(_buffer);
delay(1000); // wait a second
}
// end of code.
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The following picture shows a protoboard circuit of the project:
