CarBytes - MAX232 circuit

[David Cooley]

At 04:27 PM 11/10/1999 +1100, you wrote:
>In fact the latest incantation of Carstens interface uses a MAX232
>and a resistor and diode to combine the Tx and Rx ALDL TTL voltages.
>Carsten's original circuit had two transistors and a zener (diode),
>and I think that is was a problem, as the zener's voltage may have to be
>selected for the particular vehicle - anyway, he didn't think it was such
>a good idea (probably got too many emails asking why it didn't work!).
>
>So, are the transistors necessary (in Andrew's)? I suspect not (but I have
>not built either of these circuits) - I was just clarifying the confusion.

They give a more stable system.  The resistor/diode circuit presents more 
of a load to the bus and can cause some serious instability.
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David Cooley N5XMT Internet: N5XMT at bellsouth.net
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