Introduction to Python and Microcontrollers

LCD1602 Display

Display static text and a live-updating counter on an LCD1602 character display, controlled over I2C.

New Concepts

• Character LCD displays

LCD1602

The LCD1602 displays 2 rows of 16 characters — letters, numbers, symbols, and ASCII text.

Driven directly, the LCD1602 needs many pins. This kit’s module adds a PCF8574 I2C-to-parallel backpack, converting those many parallel pins down to just SDA/SCL — its default address is 0x27 (or 0x3F on the PCF8574A variant).

Component List

---

Circuit

Wiring Diagram

Disconnect all power before building the circuit. Reconnect once verified.

Connections:

• LCD1602 SCL → GPIO13
• LCD1602 SDA → GPIO14
• LCD1602 VCC → 5V
• LCD1602 GND → GND

Schematic Diagram

Code

File: 04_output/code/IIC_LCD1602.py Modules: 04_output/code/I2C_LCD.py, 04_output/code/LCD_API.py

import time
from machine import I2C, Pin
from I2C_LCD import I2cLcd

i2c = I2C(scl=Pin(13), sda=Pin(14), freq=400000)
devices = i2c.scan()
if len(devices) == 0:
    print("No i2c device !")
else:
    for device in devices:
        print("I2C addr: "+hex(device))
        lcd = I2cLcd(i2c, device, 2, 16)

try:
    lcd.move_to(0, 0)
    lcd.putstr("Hello,world!")
    count = 0
    while True:
        lcd.move_to(0, 1)
        lcd.putstr("Counter:%d" %(count))
        time.sleep_ms(1000)
        count += 1
except:
    pass

How to Run

Online

1. Open Thonny → 04_output/code/.
2. Right-click I2C_LCD.py and LCD_API.py → Upload to / — wait for both to finish uploading.
3. Double-click IIC_LCD1602.py.
4. Click Run current script — “Hello,world!” appears on row 1, and a counter increments on row 2 once per second.

---

Code Explanation

Scan the I2C bus

i2c = I2C(scl=Pin(13), sda=Pin(14), freq=400000)
devices = i2c.scan()

scan() checks every possible address and returns a list of devices that respond — useful since the LCD’s I2C address depends on which backpack chip variant it uses (0x27 vs 0x3F).

Create the LCD object

for device in devices:
    print("I2C addr: "+hex(device))
    lcd = I2cLcd(i2c, device, 2, 16)

Builds an I2cLcd for whichever address was found, configured for 2 rows × 16 columns.

Position the cursor and write text

lcd.move_to(0, 0)
lcd.putstr("Hello,world!")

move_to(column, row) positions the cursor (0-indexed); putstr() then writes a string starting there.

Update one line repeatedly

while True:
    lcd.move_to(0, 1)
    lcd.putstr("Counter:%d" %(count))
    time.sleep_ms(1000)
    count += 1

Moving back to the start of row 2 each loop and overwriting it lets the counter update in place rather than scrolling the screen.

---

Key Concepts

• I2C bus scanning: i2c.scan() discovers devices and their addresses without hardcoding them
• I2C-to-parallel backpacks: chips like the PCF8574 let an otherwise pin-hungry display (LCD1602 normally needs ~16 pins) run over just 2 wires
• Cursor-addressed displays: move_to() + putstr() is the basic pattern for placing text anywhere on the screen

See Class I2cLcd for the full API reference.

Further Exploration

• Display your own text on the screen. What happens if the text is too long to fit on the screen?
• Make the text scroll

Back to Module

Adapted from Python_Tutorial.pdf Project 20.1

This site is open source. Improve this page.