OLED Screens and I2c Communication

OLED Screens and I2C Communication

ITP 348 - Making Smart Devices

Learning Objectives

• Explain what synchronous, serial communication means
• Understand key concepts behind I2C protocol
• Identify OLED configuration parameters by reading through datasheet and software library
• Implement OLED screen in a device

Improving Output

• Serial monitor is fine for debugging, but we need better output to build a device

• Let’s introduce one output device

  Introducing Organic Light-Emitting Diodes

OLEDs

OLEDs are more complex than regular LEDs and be manufactured to be thin and bendable

• OLEDs are used in high end TVs, monitors, and phones
• OLEDs are more expensive than regular LEDs

Our Micro OLED has two components

OLED screen

• Blue text on black screen
• 64 pixels (W) x 48 pixels (H)
• Operates at 3.3v
• Controlled via I2C protocol (more on this later)
• 31 pins (!)

Breakout Board

• Custom circuit board that provides access to (“breaks out”) the very delicate small pins on the screen
• This breakout board also enables the communication protocol that allows us to use only 2 pins to connect to the Photon 2

Communication

• Communicating with the screen directly is complicated but we can use a library to simplify
  • This is similar to installing software on your computer to communicate with your printer (software driver)
• Photon 2 can communicate with the screen using a protocol called I2C

What is Synchronous Communication?

Synchronous Communication

• Clock pin and data pin(s)
• Clock is an oscillating square wave
• Receiver reads data signal on clock rising edge (low to high)
• Synchronous: data sent on regular intervals controlled by a clock
• Serial: one bit at time is sent / received

I2C

• Inter-integrated Circuit (I2C) is a protocol to allow a central device to communicate with multiple “peripheral” chips
• Serial
• Synchronous
• Only two pins
  • Data (SDA)
  • Clock (SCK)

I2C Cable

• Sparkfun uses a custom cable and connector for its I2C devices called Qwiic
• Instead of connecting individual wires, you can connect a single cable
• Black (GND)
• Red (3.3v)
• Blue (SDA)
• Yellow (SCK)

I2C

• Advantages
  • Uses only 2 wires (other protocols require 4 or more)
  • Standardized across many components
• Disadvantages
  • Uses more power than some other protocols (e.g. SPI)
  • Lower transfer speed than some other protocols (e.g. SPI)

Photon 2 - OLED Screen Pin Mapping

OLED	Photon 2	Purpose	Notes
GND	GND	Ground	Ground
3V3	3V3	Power	3.3v
SDA (Blue)	SDA	Data	Serial data
SCL (Yellow)	SCL	Clock	Synchronization clock

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OLED Library

• We need a library to handle much of the complex communication with the OLED
• To install a library, go to the command palette and type Install Library
• Install the OLED library: SparkFunMicroOLED

Lab

• Connect OLED and install library
• Run sample code; Modify sample code to display Hello world!
• Finally, create an Etch A Sketch using the OLED screen with two potentiometers (to draw) and one button (to reset)
• Library code
• Library guide
• Datasheet

Lab - Etch-a-Sketch

Credit

• Photo by Sparkfun
• Photo by Sparkfun
• Images created with Fritzing
• Photo by Mika Baumeister on Unsplash