PIC18F4550 Microcontroller with SSD1306 OLED and BME280 sensor

This post shows how to build a weather station using PIC18F4550 microcontroller and BME280 barometric pressure, temperature and humidity sensor from Bosch Sensortec.
The PIC18F4550 mcu reads temperature & humidity & pressure values from the BME280 sensor and print them (respectively in °C & RH% & hPa) on SSD1306 OLED display (128×64 pixel).
The BME280 is a digital barometric pressure, temperature and relative humidity sensor from Bosch Sensortec. In this project it’s used in I2C mode.
CCS C compiler is used in this project.

The SSD1306 OLED used in this project is also configured to work in I2C mode, make sure that your display is configured to work in I2C mode, some displays need jumper placing or some soldering.

To see how to interface PIC18F4550 MCU with SSD1306 OLED display (I2C mode), take a look at the following project:
Interfacing PIC18F4550 with SSD1306 OLED

And to see how to interface PIC microcontroller with BME280 sensor using CCS C compiler, visit this post:
BME280 pressure, temperature and humidity sensor with PIC MCU

Hardware Required:

  • PIC18F4550 microcontroller     —->  datasheet
  • SSD1306 OLED display with 128×64 pixel resolution
  • BME280 sensor module (with built-in 3.3V regulator and level shifter)   —->  BME280 datasheet
  • 5V source
  • Breadboard
  • Jumper wires

Weather station using PIC18F4550, BME280 sensor and SSD1306 OLED

PIC18F4550 with SSD1306 OLED and BME280 sensor circuit:
The image below shows project circuit diagram.

Hint:
The BME280 chip works with maximum voltage of 3.6V (supply voltage range is from 1.71 to 3.6V) which means we’ve to use a 3V3 voltage regulator to supply it from a 5V source.
Also, if we’re working with a 5V system (development board, microcontroller …) like the PIC18F4550 microcontroller, we’ve to use a voltage level shifter (level converter) which converts the 3.3V (comes from the BME280 chip) into 5V (goes to the PIC18F4550) and vice versa. This level shifter is for the I2C bus lines (clock and data).
The BME280 module shown in project circuit diagram has a built-in 3.3V regulator and level shifter.

BME280 PIC18F4550 SSD1306 OLED weather station circuit

All the grounded terminals are connected together.

Generally, the BME280 module has at least 4 pins because it can work in SPI mode or I2C mode. For the I2C mode we need 4 pins: VCC, GND, SDA and SCL where:
VCC is the supply pin, it is connected to +5V,
GND (ground) is connected to circuit ground (0V),
SDA is I2C bus serial data line, connected to PIC18F4550 pin RB0 (#33),
SCL is I2C bus serial clock line, connected to PIC18F4550 pin RB1 (#34).

The SSD1306 OLED display is connected to the circuit as follows:
SSD1306 OLED GND goes to circuit ground,
SSD1306 OLED VDD is connected to circuit +5V,
SSD1306 OLED SDA pin (serial data) to pin RB0 (PIC18F4550 hardware I2C SDA pin),
SSD1306 OLED SCK pin (serial clock) to pin RB1 (PIC18F4550 hardware I2C SCL pin),
SSD1306 OLED RES pin (reset) to pin RB2.

The SSD1306 OLED display DC pin is connected to VDD which means I2C slave address of the device is 0x7A. If the DC pin is connected to ground (GND) then the I2C slave address becomes 0x78.

The SSD1306 OLED and the BME280 sensor are connected to the same I2C bus (slave devices), SCL and SDA pins of the two devices are connected to SCL (RB1) and SDA (RB0) pins of the PIC18F4550 (master device).
The I2C slave address of the SSD1306 OLED differs from the one of the BME280 sensor, this difference allows the master device (PIC18F4550) to talk to one of them (only one at a time).

In this project the PIC18F4550 microcontroller runs with its internal oscillator @ 8 MHz, MCLR pin is configured as an input pin.

PIC18F4550 with SSD1306 OLED and BME280 sensor C code:
The following C code is for CCS C compiler, it was tested with version 5.051.

To be able to compile the C code below with no error, a driver for the SSD1306 OLED display is required, its full name (with extension) is SSD1306OLED.c, download link is the one below:
SSD1306 OLED CCS C library download

For more information about this driver, visit the following post:
SSD1306 OLED Library for CCS C compiler

Also, another library for the BME280 sensor is required, its full name (with extension) is BME280_Lib.c, download link is below:
BME280 CCS C library download

after the download of the 2 library files, add both of them to project folder or CCS C compiler drivers folder.

Programming hints:
The BME280 I2C address and the reset pin of the SSD1306 OLED display are defined in the C code as shown below:

The driver files of the SSD1306 OLED display and the BME280 sensor are included in the code using the following 2 lines:

As any other I2C device, the BME280 sensor has an I2C slave address which may be 0xEC or 0xEE. This address depends on the connection of the SDO pin (used for SPI mode as serial data out or MISO), if the SDO pin is connected (directly or through resistor) to VCC (3.3V) the address will be 0xEE, and if it’s connected to GND the address becomes 0xEC.

The default I2C address of the library is defined as 0xEE and my device I2C address is 0xEC.
In the code, the definition of the I2C slave address is as shown below:

The BME280 sensor is initialized with the function BME280_begin(MODE_NORMAL) which returns 1 if ok and 0 if error. In the code the initialization of the sensor is as shown below:

Reading the values of temperature, humidity and pressure is done as shown below.
Note that the library returns the temperature in hundredths °C which means we’ve to divide it by 100, it returns the humidity in relative humidity percent (rH%) in 1024 steps which means we’ve to divide it by 1024 and it returns the pressure in Pa, to get the pressure in hPa we’ve to divide it by 100.

Temperature and pressure values are displayed on the SSD1306 OLED screen.
If there is a problem with the BME280 sensor (for example wrong device address) the screen will display Connection Error.

1 bar = 10000 Pa = 100 hPa. ( 1 hPa = 100 Pa)
Pa: Pascal
hPa: hectoPascal

Rest of code is described through comments.

Full CCS C Code:

The following small video shows the result of my hardware circuit:

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