The 16×2 LCD uses parallel mode in 4-bit wiring: RS, E, and four data lines map to specific Uno GPIOs matching the LiquidCrystal constructor in firmware. Backlight may be on a transistor switch for dimming or power saving.
Typical assignments
Exact pins follow the repo sketch—document your build on paper. RS and E control command versus data mode; D4–D7 carry nibbles. Contrast on Vo uses a 10k pot between 5 V and ground.
- RS: Register select—commands vs character data.
- E: Enable strobe for each nibble transfer.
- D4–D7: Upper four bits of the 8-bit interface in 4-bit mode.
- Backlight: Often transistor-switched LED+ pin, not a GPIO data line.
Avoiding conflicts
Do not assign LCD lines to SPI reserved pins used by the Ethernet shield. DHT22 data pins must also stay clear—see DHT22 data wiring.
Display content
What appears on each row is firmware-defined in LCD local display format.