Coins counter

FT1235 transmitter and a FT1236 receiver will works like a anti-shoplifting system. Every coin have each weight with different speed in free fall through electromagnetic coils.
FT1236 Receiver, with microprocessor’s help  can  detect the electromagnetic field changes when it is crossed. Whith arduino, for example, we have different intruments that can help us, like analogic input, interrupt ecc..
My challenge is understand how magnetic field of this wireless power kit change with different value of coins and make something like a funny moneybox with a lcd display.