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What i am making here is a USB lock with smartcard key. The idea is that a phonecard reader made with a PIC micro will be able to store a number of different phonecards into memory. Whenever one of these cards is inserted into the slot, it will activate a 4-ports USB On/Off switch. If the card is removed, the USB ports will be de-activated. [ ]

This is a Protection for Input Ports Arduino Circuit Diagram . During tests or doing some project , we run the risk of accidentally burn Arduino input . A short circuit protection can prevent a lot of problems and is one less worry , especially against accidents . It is simple , you just need a 1k resistor and a zener diode of 5 Volts , which in the case of commercial zener diode , the voltage is closer to 5.1 V and diode is the 5V1 .  Protection for Input Ports Arduino Circuit Diagram