Comments on the following:

1). First comment: If you went to a power and ground plane, you wouldn't need all that EMI stuff. :)

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As I mentioned, I'm doing a new design for a site monitor that keeps track of other modules over an RS485 LAN. It is a communications supervisor and its circuitry is all logic based and its signal speeds are governed by baud rates.

To make the initial production runs go smoothly, I prefer to spend a little extra on safety components. I can always remove them later.

The unit is mostly SMT, double-sided, no ADC/DAC encoding, all logic, no external microcontroller bus, three crystals at 18MHz,4MHz and 32Khz very short lead direct ICs. The only high speed signal traces are the IrDA data when they are active. ALE external clocking is turned off.

I believe in putting ferrite beads on signals leaving the metal case just as insurance to help during FCC emissions testing. Its always easier to remove them and to add them later. The only signals leaving this product are RS232 signals, RS485 LAN, power and an auxilary relay contacts to an optional alarm.

Size 0805 ferrite beads are recommended as more available than 0603. I'm not sure I want to waste the board space with 0805s. I may look for SMT packages with several per unit.

Control panel buttons and ibutton readers are protected from +-15Kv static spikes.

The In-System-Programming (ISP) port has additional protection on the RESET pin that goes to a microsupervisor chip (MAX812). Obviously no ferrite beads there since its a factory-use port.

Three EMI filter chips will be used: on the uC, an IrDA coder, and another PLCC chip. The DC power input goes through a hefty muRata chip filter.

I understand that a power and ground plane would make a lot of problems go away, but its not going to happen on this design. The unit is in a very small aluminum case and is chassis grounded.

aka j