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House of Hundreds II (Smart 3-Digit Subtraction Vault)

Source:

Solve 3-digit subtraction problems (e.g. 523 - 267) on a smart vault keypad. When borrowing is required (3 - 7 cannot be done!), a servo motor physically unlocks 1 Ten bundle into 10 loose Ones.

Categorisation

Props & Materials Required

  • •Smart vault cabinet with 3 drawer compartments (Hundreds, Tens, Ones)
  • •Servo motor (opens Tens-to-Ones borrowing chute)
  • •4x4 membrane keypad
  • •ESP32 controller board
  • •0.96-inch OLED display
  • •DFPlayer Mini MP3 module + 3W speaker

Step-by-Step Instructions

1

Input Subtraction Problem

Key in '523 - 267' on the vault keypad.

2

Ones Column Subtraction Check

Look at Ones: 3 minus 7. Speaker alerts: 'Cannot subtract 7 from 3! We must BORROW 1 Ten!'

3

Servo Unlocks Borrow Chute

Servo motor activates! A drawer opens dispensing 10 loose ones into the Ones cup. Now you have 13 Ones!

4

Complete Subtraction

13 - 7 = 6 Ones! Continue to Tens (11 - 6 = 5 Tens) and Hundreds (4 - 2 = 2 Hundreds). Display: '256'.

Why It Works & Notes

Borrowing (regrouping) in 3-digit subtraction is a major milestone. When the child tries to subtract 7 from 3, a servo motor opening a compartment to convert 1 Ten into 10 Ones makes borrowing physically understandable.