OLED Screens (old SPI version)

OLED Screens and SPI Communication

Note: Old Version with SPI

• The following describes the SPI version of the OLED screen
• This OLED is no longer used in our class
• Please see the I2C version of the OLED screen

ITP 348 - Introduction to Physical Computing

Learning Objectives

• Explain what synchronous, serial communication means
• Understand key concepts behind SPI 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 (H) x 48 pixels (W)
• Operates at 3.3v
• Controlled via I2C or SPI 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 allows us to connect up to 16 pins, but we only need to worry about the top 8 pins

Breakout Board Pins

##

OLED	SPI Function	Notes
GND	Ground	Ground
3V3	Power	3.3v
D1 (SDI)	MOSI	Serial data in
D0 (SCK)	SCK	SPI clock
D2 (SDO)	MISO	Unused
D/C	Data / Command	Specify incoming byte as command or screen data
RST	Reset	Active-low reset (3.3v to enable)
CS	CS	SPI chip select (active-low)

</span>

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 two different protocols: SPI or I2C
• We will discuss I2C later in the course

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

What is Serial Peripheral Interface (SPI)?

• SPI is one implementation of serial synchronous communication to send and receive data between devices
• Synchronous: data is sent on regular intervals controlled by a clock
• Serial: one bit at time is sent / received
• Terminology:
  • Photon 2 will be called main
  • OLED (peripheral) will be called secondary

SPI Structure

SPI Structure

• Two data pins for bidirectional communication (one for sending data, one for receiving)
• Data from Photon 2 (Main Out) to OLED (Secondary In) is the MOSI pin
• Data to Photon 2 (Main In) from OLED (Secondary Out) is the MISO pin

Additional Pins

• SPI also includes a CS (chip select) pin, which is used to specify which secondary device is active
  • e.g. if you were controlling multiple OLED screens
• OLED screen includes a D/C pin to distiguish between commands (e.g. clear screen) and data (e.g. display byte 01001011)

Photon 2 - OLED Screen Pin Mapping

see next slide ##

OLED	Photon 2	SPI Function	Notes
GND	GND	Ground	Ground
3V3	3V3	Power	3.3v
D1 (SDI)	MO	MOSI	Serial data in
D0 (SCK)	SCK	SCK	SPI clock
D2 (SDO)	-	MISO	Unused
D/C	Digital Pin	Data / Command	Specify incoming byte as command or screen data
RST	Digital Pin	Reset	Active-low reset (3.3v to enable)
CS	Digital Pin	CS	SPI chip select (active-low)

</span>

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
  • Use: D/C (pin D5), RST (pin D6), CS (pin D7)
• 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