Interfacing Arduino with ST7735 display and DS18B20 temperature sensor

This post shows how to implement a simple temperature measurement station using Arduino UNO board and DS18B20 digital temperature sensor.
The Arduino reads temperature (in °C) from the DS18B20 sensor and print its value 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.

The DS18B20 temperature sensor is a 3-pin electronic component (like a simple transistor) from Maxim (formerly Dallas) which uses 1-wire protocol to communicate with master device (microprocessor, microcontroller ….). Each DS18B20 device has a unique 64-bit serial code, which allows multiple DS18B20s to function on the same 1-wire bus and controlled with one master device.
The DS18B20 sensor provides 9-bit to 12-bit Celsius temperature measurement resolution (programmable resolution).

To see how to interface Arduino with ST7735 TFT display, visit the following post:
Arduino ST7735 1.8″ TFT display example

Hardware Required:

  • Arduino board
  • ST7735S (ST7735R) TFT screen
  • DS18B20 temperature sensor    —->   datasheet
  • 5 x 1k ohm resistor
  • 4.7k ohm resistor
  • Breadboard
  • Jumper wires

Arduino with DS18B20 sensor and ST7735 TFT display circuit:
The image below shows project circuit diagram.

The DS18B20 sensor has 3 pins (from right to left): VCC (or VDD), data and GND where:
VCC (VDD): sensor power supply pin, connected to Arduino 5V pin,
data pin: connected to Arduino analog pin 0 (A0) and
GND: connected to Arduino GND pin.

A pull-up resistor of 4.7k ohm is required because the DS18B20 output is open drain.

Arduino DS18B20 ST7735 TFT temperature station

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 DS18B20 sensor code:
The following Arduino code requires 2 libraries from Adafruit Industries:
Adafruit ST7735 display library
Adafruit graphics 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 file.

The previous 2 libraries are included in the main code as follows:

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:

Functions used in the code:
bool ds18b20_start(): used to know if the DS18B20 sensor is correctly connected to the circuit, returns 1 if OK and 0 if error.
ds18b20_write_bit(bool value): writes (sends) 1 bit to the DS18B20 sensor, the bit is ‘value‘ which may be 1 or 0.
ds18b20_write_byte(byte value): writes 1 byte (8 bits) to the DS18B20 sensor, this function is based on the previous function. This function writes LSB first.
bool ds18b20_read_bit(void): reads 1 bit from the DS18B20 sensor, returns the read value (1 or 0).
byte ds18b20_read_byte(void): reads 1 byte from the DS18B20 sensor, this function is based on the previous function. This function reads LSB first.
bool ds18b20_read(int *raw_temp_value): reads the temperature raw data which is 16-bit long (two 8-bit registers), the data is stored in the variable raw_temp_value, returns 1 if OK and 0 if error.

The value of the temperature in degree Celsius is equal to the raw value divided by 16 (in case of 12-bit resolution). The default resolution of the DS18B20 is 12 bits ( ==> thermometer resolution = 0.0625°C).

Full Arduino code:

The following picture shows a protoboard circuit of the project:

Arduino UNO with ST7735S color display and DS18B20 digital temperature sensor

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