LCD1602 hello on an Arduino Uno

// LCD1602: a greeting on the top line and a seconds counter under it.
//
//   LCD RS -> pin 12    LCD E  -> pin 11
//   LCD D4 -> pin 5     LCD D5 -> pin 4    LCD D6 -> pin 3    LCD D7 -> pin 2
//   LCD VSS, RW, K -> GND     LCD VDD, A -> 5V
//   LCD V0 -> GND here for full contrast (a kit wires a 10k potentiometer)
//
// The display has its own controller, the HD44780, and it is talked to four
// bits at a time on D4 to D7 so that only six pins are used. RS says whether
// the bits are a command or a letter, and a pulse on E says "take them now".
// The LiquidCrystal library does all of that; print() feels like Serial.

#include <LiquidCrystal.h>

LiquidCrystal lcd(12, 11, 5, 4, 3, 2);

unsigned long shown = 0xFFFFFFFF;

void setup() {
  lcd.begin(16, 2);
  lcd.print("Hello, kit!");
  Serial.begin(9600);
  Serial.println("Mokxi Uno: LCD1602 hello");
}

void loop() {
  unsigned long seconds = millis() / 1000;
  if (seconds != shown) {
    shown = seconds;
    lcd.setCursor(0, 1);
    lcd.print("Up ");
    lcd.print(seconds);
    lcd.print(" s");
    Serial.print("up ");
    Serial.print(seconds);
    Serial.println(" s");
  }
}