> From: Rob Roy <nqsage@HOTMAIL.COM>
>  I was wondering if anyone has wrestled with trying to eliminate rs232
> line drivers and their associated capacitors from a dongle like device
> attached to a PC or similar serial port  I know that I can use a MAX232A
> to convert my 16c5X software UART lines to serial levels and vice versa,
> however I was wondering since resistors and diodes are cheaper and my
> supply voltage is +10v & -10v whether I could condition my input serial
> line with a resistor and a zener like so:
>                 10k
> in>------/\/\/\/\/\---------------------------<PIC
>                                   |   /
>                                ------
>                              /   A        3.3v
>                                  ---
>                                   |
>                                ///

You are not need 10K resistor if you use any PIC's input orther then RA4
that have no
diodes.

> and do something as simple with the output like
>                                  |/---------/\/\/\/\/\/-------<+10v
> PIC>-----/\/\/\----------|
>                                  |\
>                                  |----------/\/\/\/\/\---------<-10v
>                                  |
>                                  |-----<TXD (to RXD input of PC Serial
Port)

2 years ago I've posted here the schematic with single +5 power :
                                  ______ +5v
                            b |/e
PIC--------/\/\/\/-------|       p-n-p tranzistor
output                     |\c
                                  \
                                   |---------------------------  TxD  (to
PC's RxD )
                                   |       4k7      10-100mF
                                    ---/\/\/\/\/--------||-----|
                                                    _\/_  diode
PIC                                                 |
input -----/\/\/\/\---------------------------------------- RxD (to PC's
TxD)


One thing - do not use this at the high speed (38400 and more), use ADM232
(MAX232).


Alex Torres, Kharkov, Ukraine (exUSSR)
altor@chat.ru
2:461/28@FidoNet
http://www.geocities.com/SiliconValley/Lab/6311