best way to protect the input of a PIC microcontroller

[kiks]

PIC Input protection

What is the best way to protect the input of a PIC microcontroller, for eg if an external micro switch is connected to an input pin? What is common practice and offers good protection.

 

[kender]

PIC Input protection

A small resistor (typically 20R - 100R) in series with the I/O pin would offer some protection. Cheapest protection.
Transient voltage suppressors (TVS) also help against ESD.
Galvanic isolation of the switch with optical or magnetic coupler would offer the most protection.

 

[btbass]

Re: PIC Input protection

The input pin has internal clamping diodes to protect it against voltage excursions, a series current limiting resistor will protect the diodes from exsessive current.
Place a 1nF 200V ceramic cap on the pin to ground where the micro switch connects to the board.
A series current limiting resistor of 100R will offer little or no protection. We use a value of 33K, 0805 placed close to the pin. This protects against 8KV static discharges during EMC testing.
The input impedance of the pin is very high. The 33K will not effect the function of the input.