I'd like to connect R-Pi serial to PC's RS232 port without IC (such MAX3232), using only diode (thus block negative voltage to 0V), voltage divider resistors, and common BJT.
For TXD (RX from R-Pi perspective): Using my USB-to-RS232 adaptor, measured voltage level for logic high is 7.5V, 6.85V after 0.65V diode voltage drop, so I'll use 270:220 ohm resistor for 3.07V (for 10 mA current) - 3.36V (no current, no voltage drop) divided voltage. Current is limited to about 10 mA with 490 (270+220) ohm resistance.
For RXD (TX from R-Pi perspective): Borrowing power from DTR line, switch it using BC557 PNP transistor (DTR to collector; emitter to RXD) with base connected to R-Pi's TX in series with 680K resistor (for limiting drawn current to 0.5 mA).
My question is: will this work? (I'm not sure whether impedance of the connected pins will affect this simple circuit). Thanks in advance for your response.