Vending Machines: How They Know It’s a Quarter

You feed a vending machine a quarter. It accepts it. You feed it a washer of the exact same size. It spits it out. How does it know? It’s not looking at the face of George Washington. It’s tasting the metal.

Electromagnetic Signature

As the coin rolls down the chute, it passes through magnetic coils.

1. Size: Light sensors measure the diameter.
2. Metal Content: The coils induce a magnetic field.
   • Copper, Nickel, and Zinc all react differently.
   • The machine measures the change in inductance.
   • “This object is 24.26mm wide and is made of 91.67% Copper and 8.33% Nickel.” -> It’s a Quarter.

Robotics: The Color Sorter

In FTC games, we often have Red and Blue game pieces mixed together. If you score the wrong color, you get a penalty. We put a Color Sensor in our intake tube.

1. LED: Shines a bright white light on the ball.
2. Sensor: Measures the reflected light (R, G, B values).
3. Logic:
   • if (Red > 200) { Eject(); } (If on Blue Team).
   • if (Blue > 200) { Keep(); } It’s the same logic as the vending machine: Filter the inputs, keep the treasure, reject the trash.