I have two PCs (very old, without usb but rs232 port) that talks via RS232. They send to each other very small bit of info ( one character every 10sec). Now I need to connect additionally two sensors that send data to first PC. I assume no collision for all devices. I have tried to make all devices TTL lvl using MAX232 and it works only for two devices sending data to PC1 (e.g. PC2 and sensor1). When I connect sencond sensor (like on schematic) then there is no communication at all. I guess the MAX232 input in PC1 goes overload for 3 devices. Question - Do you know how to make it right for 3 devices? Maybe tying up Tx pins of both sensors on RS232 lvl and then put it to one MAx232? Any solutions with no use Rs485? (I have no handshakes..)
EDIT: Here is schematic that would do the trick. Reply provided by Wouter van Ooijen.