I want to connect a relay to a PC RS232 (serial) port, than use programming control this on or off. I test the serial port pin 3 voltage allway in high level when I set it low in program. I found some information from internet that the serail port need a interface for its external devices.
Please if you know how is this interface circuit, show me the circuit. simple is the best. for control a LED or a relay.
Thank you all.
Please if you know how is this interface circuit, show me the circuit. simple is the best. for control a LED or a relay.
Thank you all.