In this update, we want to demonstrate how easy it is to get common devices up and running on Giant Board. By using a U-Boot device tree overlay that enables common interfaces like I²C and SPI, you can easily leverage CircuitPython to communicate with a great number of devices. In this brief overview, we will pull data from an Adafruit BMP280 sensor and render it on an Adafruit OLED FeatherWing display.
The display is a 128x32 OLED screen and the BMP280 is a temperature
and barometric pressure sensor. We plan to use both devices via I²C,
which is easy to setup. All Giant Board images come with most of the
interfaces disabled, so we’ll need to enable I²C using one of the
provided device tree overlays. You can do that simply by editing the
text file located at
/boot/uboot/uEnv.txt. You will want to:
When you’re done, it should look something like the image below.
Once you have made those edits, a simple reboot will bring up the I²C
interface. To verify this, you can type
ls /dev/i2c-*. You should
see two I²C buses:
I2C-1. If you see both buses,
everything should be set for the CircuitPython steps below.
We went over to Adafruit’s learning guides to get some basic sample code. We recommend testing each of these examples individually, to verify that both devices are working, before you combine them into a single project.
The basic code pulled from Adafruit’s BMP280 CircuitPython examples should produce the following output:
That code should be nearly identical to the following:
from time import sleep as wait import board # import digitalio # For use with SPI import busio import adafruit_bmp280 # Create library object using our Bus I2C port i2c = busio.I2C(board.SCL, board.SDA) bmp280 = adafruit_bmp280.Adafruit_BMP280_I2C(i2c) # OR create library object using our Bus SPI port #spi = busio.SPI(board.SCK, board.MOSI, board.MISO) #bmp_cs = digitalio.DigitalInOut(board.D10) #bmp280 = adafruit_bmp280.Adafruit_BMP280_SPI(spi, bmp_cs) # change this to match the location's pressure (hPa) at sea level bmp280.sea_level_pressure = 1013.25 while True: print("\nTemperature: %0.1f C" % bmp280.temperature) print("Pressure: %0.1f hPa" % bmp280.pressure) print("Altitude = %0.2f meters" % bmp280.altitude) wait(2)
The next step is to test the OLED FeatherWing to make sure that it, too, is working as intended. We used the sample code here, which should display three dots on the screen, as shown below:
The code itself looks like the following:
# Basic example of clearing and drawing pixels on a SSD1306 OLED display. # This example and library is meant to work with Adafruit CircuitPython API. # Author: Tony DiCola # License: Public Domain # Import all board pins. from board import SCL, SDA import busio # Import the SSD1306 module. import adafruit_ssd1306 # Create the I2C interface. i2c = busio.I2C(SCL, SDA) # Create the SSD1306 OLED class. # The first two parameters are the pixel width and pixel height. Change these # to the right size for your display! display = adafruit_ssd1306.SSD1306_I2C(128, 32, i2c) # Alternatively you can change the I2C address of the device with an addr parameter: #display = adafruit_ssd1306.SSD1306_I2C(128, 32, i2c, addr=0x31) # Clear the display. Always call show after changing pixels to make the display # update visible! display.fill(0) display.show() # Set a pixel in the origin 0,0 position. display.pixel(0, 0, 1) # Set a pixel in the middle 64, 16 position. display.pixel(64, 16, 1) # Set a pixel in the opposite 127, 31 position. display.pixel(127, 31, 1) display.show()
Once you have confirmed that both devices are working, you can use them together to display sensor data – pulled from the BMP280 – on the OLED FeatherWing. To make this easier, we found another example from Adafruit that shows how to display text on the OLED FeatherWing. Using that code as a guide, we ended up with the Python program at the very end of this update. That program displays nicely formatted temperature, pressure, and altitude information on the FeatherWing’s OLED screen:
From here you can customize the program to include the time, CPU usage, RAM usage, or anything else you’d like to display. CircuitPython simplifies the use of external hardware so that you can stay focused on your actual project. When prototyping, this allows you to make a great deal of progress in a short period of time.
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from time import sleep as wait import subprocess from PIL import Image, ImageDraw, ImageFont # Import all board pins. from board import SCL, SDA import busio # Import the SSD1306 module. import adafruit_ssd1306 # Import the BMP280 module import adafruit_bmp280 # Create the I2C interface. i2c = busio.I2C(SCL, SDA) # Create the SSD1306 OLED class. # The first two parameters are the pixel width and pixel height. Change these # to the right size for your display! display = adafruit_ssd1306.SSD1306_I2C(128, 32, i2c) # Alternatively you can change the I2C address of the device with an addr parameter: #display = adafruit_ssd1306.SSD1306_I2C(128, 32, i2c, addr=0x31) # bmp280 class bmp280 = adafruit_bmp280.Adafruit_BMP280_I2C(i2c) # change this to match the location's pressure (hPa) at sea level bmp280.sea_level_pressure = 1008.46 # Clear the display. Always call show after changing pixels to make the display # update visible! display.fill(0) display.show() # Create blank image for drawing. # Make sure to create image with mode '1' for 1-bit color. width = display.width height = display.height image = Image.new('1', (width, height)) # Get drawing object to draw on image. draw = ImageDraw.Draw(image) # Draw a black filled box to clear the image. draw.rectangle((0, 0, width, height), outline=0, fill=0) # Draw some shapes. # First define some constants to allow easy resizing of shapes. padding = -2 top = padding bottom = height-padding # Move left to right keeping track of the current x position for drawing shapes. x = 0 # Load default font. font = ImageFont.load_default() while True: draw.rectangle((0, 0, width, height), outline=0, fill=0) draw.text((x, top), "Temperature: %0.1f C" % bmp280.temperature, font=font, fill=255) draw.text((x, top+10), "Pressure: %0.1f hPa" % bmp280.pressure, font=font, fill=255) draw.text((x, top+20), "Altitude: %0.2f m" % bmp280.altitude, font=font, fill=255) # Display image. display.image(image) display.show() wait(2)
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