[Lab] simple 5.5V<->3.3V interface for 1-wire

[Peter Sjoberg]

On Mon, 2012-12-24 at 11:57 -0500, Richard Guy Briggs wrote:
> On Mon, Dec 24, 2012 at 11:41:01AM -0500, Peter Sjoberg wrote:
> > what's the safest way to read 5V with raspberry pi's 3.3V
> > unbuffered input short of buying some chip?
> 
> A voltage divider will easily do that.
> 
> ------+
>       \
>       / 10k
>       \
>       /
> 5V    +----------
>       \
>       / 18k
>       \        3.3v
>       /
> ------+----------
> 
> Use proportionately higher values if there is too much loading on your data
> line.
> 
I know enough basic electronics to know about a resistor voltage divider
about but I forgot one important detail in my question - bidirectional.
I don't think I can send 3.3V out and get 5V and if I put >5V with
resistor somewhere I above I have to think a bit about values, currents
and so on to not interfere with the signal.

/ps