I2C LCD Screen

I2C LCDs

LCDS Output Screens

• Let’s introduce the humble LCD

Liquid Crystal Display (LCD)

LCDs

• Output device that display text in rows and columns
• Can be use for simple graphics, but primarily for text
• Relatively cheap
• Passive, low power

LCD Pixels

LCD Come in Many Different Sizes and Colors

Basic wiring

Basic Wiring

• The standard wiring of an LCD uses 16 wires (requiring 12 pins on the Photon 2)!
• The condensed wiring use 12 wires (requiring 8 pins on the Photon 2)!
• Writing code to communicate with the LCD is challenging (more on that later)

Basic wiring Condensed

Basic wiring Condensed

• 4 pins for power (2 for LCD, 2 for backlight
• 4 pins for controlling LCD
• 8 (or 4) pins for data (the text you want to display)

Parallel LCD

• There are 8 pins for data when operating in parallel

• Let’s say you want to display the letter Q

• The letter Q is represented on a computer by the binary string 01010001

• Each bit will be transmitted on a separate data pin

Serial LCD

• Thankfully there is a better solution!
• What is a serial communication?
• What serial protocols have used so far?

What is Synchronous Communication?

• Data pin and clock pin

• Clock is an oscillating square wave
• On rising (low to high) or falling (high to low) edge, the receiver samples (“read”) data line

Serial, Synchronous Communication

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 Transmission

I2C Transmission - Part 1 Address

I2C Transmission - Part 2 Data

I2C Addresses

• Since multiple devices might be connected on the same two wires, many devices are “listening” to the communication
• Each device is given a 7-bit address to distinguish it from anyone devices
  • 0000000 - 1111111 (binary)
  • 0 - 127 (decimal)
  • 0x0 - 0x7F (hexadecimal)
• These addresses are often fixed and specified on the hardware device

I2C vs SPI

I2C	SPI
Uses 2 wires	Uses 4 wires; more devices means even more wires
Uses more power	Uses less power
Lower transfer speed	Higher transfer speed
Standardized	Multiple “versions”

I2C Serial Backpack

I2C Serial Backpack

• A “backpack” is a component that is added on another device
• The I2C backpack (black-colored logic board) translates the 8 pin parallel communication to 2 pin serial communication
• The blue potentiometer can be used to adjust the contrast
• Jumper on the left acts like a removeable switch to control LED backlight

Serial I2C LCD Wiring

LCD	Photon 2	Function	Notes
GND	GND	Ground	Ground
VCC	VUSB	Power	must be 5v
SDA	SDA	data line
SCK	SCK	clock

Special Notes

• SDA and SCL lines need pullup resistors (4.7k or 10k) to 3V3 (not VUSB)
  • Particle documentation reference
• VCC on LCD goes to VUSB (otherwise it will be very light and hard to read)

Exercise 1

• Download project: Go to https://tinyurl.com/ProjectZipGH
• Paste the following link into the top right https://github.com/reparke/TAC348-Making-Smart-Devices/tree/main/_exercises/week13/ultrasonic_start
• Connect I2C LCD and run example code
• Recommended library for the Photon 2:
  • LiquidCrystal_I2C_Spark

Exercise 2

• Connect ultrasonic range finder and displace distance to object on LCD
  • Trigger: D3
  • Echo: D4
• Use RGB LED to alarm: green for n

Credit

• Sparkfun
• Sparkfun
• Sparkfun