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OLED example

Device

Specification

  • Size: 0.96 inch
  • Resolution: 128 x 64
  • Color: Blue & Yellow
  • Visible angle: 160 degrees or more
  • Support platforms: arduino 51 series, MSP430 series, STM32/2, CSR chip, etc.
  • Ultra low efficiency consumption: normal 0.04 W.
  • Wide voltage support: DC 3.3V-5V
  • Drive Chip: SSD1306
  • Communication Method: IIC, I/O ports only 2
  • No font: take software word

Pins

  • VCC: 3.3V-5V
  • GND: Power Ground
  • SCL: CLK Serial
  • SDA: Serial Data

Circuit

Client environment

  • IDE: Arduino IDE 1.8.10 (on MacOS Catalina 10.15.7)
  • Board: ATtiny3216 breakout board
  • Libraries:
    • Adafruit SSD1306 ver. 2.4.4
    • Adafruit GFX-Library ver. 1.10.7

Networking

I2C address

Check I2C address by the position of 0Ω resister in “Address Select” area at OLED.

position I2C address memo
0x78 0x3C <–
0x7A 0x3A

Pin map

PORT PIN ATtiny3216 OLED Memo
VCC VIN(+5V) +5V: 6-pin FTDI-Serial, 3pin UPDI programmer
GND GND GND Ground: 6-pin FTDI-Serial, 3pin UPDI programmer
PB0 SCL SCL
PB1 SDA SDA
PB2 (7, TXD) 6-pin FTDI-Serial
PB3 (6, RXD) 6-pin FTDI-Serial
PA0 (17, UPDI) 3pin UPDI programmer

OLED connection

Program

Install libraries

Arduino IDE > Tool > Manage Libraries…

  • Adafruit SSD1306 ver. 2.4.4
  • Adafruit GFX-Library ver. 1.10.7

(Optional) Check library source code

Note

Some old sample requires to change the definition of I2C address in Adafruit_SSD_1306.h. However, it seems current library does not require that (there are no field to define I2C address at the header file. )

Library file is located at the place like <the sketch location path>/libraries/Adafruit_SSD1306

Sketch location is at Arduino IDE > preferences > sketchbook location

Arduino Sketch loc

Arduino Sketch loc2

Program (edit example)

Arduino IDE > File > Examples > Adafruit SSD 1306 > ssd1306_128x64_i2c

Change the line arround line no:35

  • Before

    1
    #define SCREEN_ADDRESS 0x3D

  • After

    1
    #define SCREEN_ADDRESS 0x3C

I2C address conversion

“0x78” address on OLED board is 7bit mode + 1 bit R/W#bit at the end.

  • 0x78 = 0b01111000 <- the last bit(0111100”0”) is “R/W#bit”.
  • Wire.beginTransmission(address) in Arduino Wire library (used in Adafruit_SSD1306 display()) requires address parameter in 7 bit.
  • For doing this, dropping the last bit (meaning shift the value one bit to the right)
    • 0b01111000
    • 0b0111100 = 0x3C, dropped the last bit

Ref. Wire library

There are both 7- and 8-bit versions of I2C addresses. 7 bits identify the device, and the eighth bit determines if it’s being written to or read from. The Wire library uses 7 bit addresses throughout. If you have a datasheet or sample code that uses 8 bit address, you’ll want to drop the low bit (i.e. shift the value one bit to the right), yielding an address between 0 and 127. However the addresses from 0 to 7 are not used because are reserved so the first address that can be used is 8.

Write program by UPDI

  • Arduino IDE > Tool
    • Board: ATtiny3216
    • Port: /dev/cu.usbserial-D307RG9Y
    • Programmer: “Serial Port and 4.7k(pyupdi style)”

Then write program by “Upload” function

Outcomes

ssd1306_128x64_i2c

OLED example1

PoTone display, FA2020 :)

PoTone display

Source code

The other tips

  • Pullup resister for I2C

    You must be sure to use external pullup resistors on the SDA and SCL lines if the devices you are connecting do not have those on board (many Arduino/hobby targeted breakout boards do - typically 10k - though these may need to be enabled with a solder-bridge or jumper). The 30k-50k internal pullup resistors are not suitable for I2C pullup resistors; while they were enabled by megaTinyCore prior to version 2.1.0, this was the worst of both worlds: they often did work with the simple test case, leading the developer on their merry way thinking they were all set, only to discover that when they added another I2C device or two, or moved the device to the end of a longer cable, I2C suddenly no longer worked - it’s probably better for it to fail immediately, prompting investigation and subsequent addition of appropriate pullup resistors.

  • SpenceKonde/megaTinyCore#i2c-twi-support - TWI Pins: Switch SCL/SDA pins to the other set by Wire.swap(1) or Wire.swap(0). It looks default(0) means PB0: SCL, PB1: SDA on Attiny3216

References

Last update: April 30, 2021