piclist 1995\12\08\202512a >
Thread: Direct RS-232 Connect
www.piclist.com/techref/io/serials.htm?key=rs%2D232
picon face BY : Henry Carl Ott email (remove spam text)



Lee Jones <TakeThisOuTleespamBeGonespamEraseMEFRUMBLE.CLAREMONT.EDU> wrote:

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If you need that negative voltage...

 I slapped together a 16c54 based data logger that would download recorded
data to a PC over the RS-232 port. I wanted to be able to to talk to the
logger with a standard terminal program to set the current date/time and
also to instruct it to do a data dump. I also wanted it small (final design
with an eeprom, I2C RTC, and battery was the size of a match box).
 Data was bi-directional but half duplex. I used the standard current
limiting resister trick for the pc to pic link (with a diode) but then I
used the pc tx line as a negative voltage source for the pic to pc link
(with a resister and a npn transistor). Minor note: anything the pc sends
the pic is echoed back through the bias resister. The circuit worked fine,
(even with the pic running on a 3volt lithium cell) but as mentioned earlier
this is definitely a mickey mouse solution. I would not trust it in
production designs.

Hope this helps a bit.....


carl

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