Science Fair Iron Repulsion Electromagnet

I need a compact, student-friendly iron-repulsion electromagnet that can serve as the centerpiece of a science-fair exhibit. The core requirement is a coil system that pushes a small iron slug or plate away with visibly adjustable force.

Key functions to build in: adjustable repulsion strength (a dial or digital control that varies current), wireless or IR remote control for hands-off demos, and a simple safety lock that cuts power instantly if something behaves unexpectedly. Because the device will be handled by middle- and high-school students, absolute electrical safety and clear operating instructions are essential.

To make the project reproducible, I will need:
• A working prototype capable of at least three distinct strength settings and a demonstrable off-site trigger via remote.
• Full schematic, PCB (or perf-board) layout, and BOM with readily available components.
• Firmware or control code (if a microcontroller or Bluetooth module is used) plus a brief comment guide.
• Step-by-step assembly and usage guide, including safety notes that a teacher can follow.

Acceptance criteria: the finished unit must repel a 10 g iron slug a minimum of 3 cm at the highest setting, run safely from a 12 V DC source, and survive continuous operation in five-minute demonstration cycles without overheating.