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House of Hundreds I (Smart 3-Digit Addition Cash Register)

Source:

Insert play bank notes (₹100, ₹10, ₹1) into a cash register with IR slot sensors. The machine adds 3-digit amounts (e.g. ₹245 + ₹138) and demonstrates carrying over when 10 Tens become 1 Hundred.

Categorisation

Props & Materials Required

  • •Cardboard cash register housing with 3 bill slots (Hundreds, Tens, Ones)
  • •3x IR slot sensors (detects bills inserted)
  • •3-digit 7-segment LED display
  • •ESP32 / Arduino controller
  • •DFPlayer Mini MP3 module + 3W speaker

Step-by-Step Instructions

1

Insert First Amount

Insert two ₹100 notes, four ₹10 notes, and five ₹1 coins (₹245). Display shows '245'.

2

Insert Second Amount to Add

Insert one ₹100 note, three ₹10 notes, and eight ₹1 coins (₹138).

3

Watch Carrying Over Action

5 ones + 8 ones = 13 ones! The machine beeps: '10 Ones regroup into 1 Ten!' Tens display increments by 1.

4

Final Sum Announcement

Display shows total '383'. Speaker narrates: '245 + 138 = 383 rupees! Addition completed with 1 carry over!'

Why It Works & Notes

3-digit addition carrying over (regrouping) is hard when abstract. Physically feeding ten ₹10 notes into a slot and seeing the machine convert them into one ₹100 bill makes carrying over crystal clear.