Beginner 10 — Count five boxes (CTU)

Briefing

A conveyor fills a carton with boxes. Tap START — the MOTOR runs. Each time a box trips the BOX_EYE photo-eye, the counter adds one. After five boxes the carton is full: MOTOR stops and the CARTON_FULL lamp turns on. Tap CNT_RESET to clear the count and lamp so the next carton can begin. A CTU ("Count Up") is a function block just like the TON timer. You declare an instance in VAR, call it with a rising-edge input (CU) and a preset value (PV), and read its .Q output bit when the count reaches PV.

Objectives

• Tap START → MOTOR runs, CARTON_FULL off
• Five BOX_EYE pulses → MOTOR stops and CARTON_FULL turns on
• Tap CNT_RESET → count clears, CARTON_FULL off, conveyor can restart

I/O Table

Your program will be tested against:

All test cases run automatically when you submit. Assertions are hidden until you pass.

1. #1Tap START → MOTOR on, CARTON_FULL off

   A momentary START latches MOTOR on before any boxes are counted

2. #2Five BOX_EYE pulses → CARTON_FULL on, MOTOR off

   Five rising edges on BOX_EYE triggers CTU.Q which stops motor and lights lamp

3. #3Three BOX_EYE pulses → MOTOR still on, CARTON_FULL off

   Fewer than five pulses: counter has not reached PV so conveyor keeps running

4. #4CNT_RESET after full carton → lamp off, conveyor can restart

   After CARTON_FULL, CNT_RESET clears the counter so START latches the motor again