I would use RS485. There are some excellent line drivers such as the
SN75176 and the MAX485. It is a balanced signal, so you will need two
signal wires. An upside is that you can do bidirectional communications
on the bus. Downside is that you will need to develop your own protocol
to avoid collisions and such.

Hope that helps,

Josh
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Andreas Doktar wrote:
>
> I'm having this design problem:
>
> I have a couple of PIC16F84:s that have to communicate with each other.
> I'm going to use some kind of asyncronous serial protocol. But when the
> PIC:s are about 50 meters from each other, what is the smartest way to
> connect them?
<snip>
> Alt III
> Some kind of bi-directional buffer. Which part would be suitable?

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