hi... im posting the ckt diagram. jus the main ckt of FP module and GSM module. The relay is a 5V relay and is activated and deactivated by microcontroller through pin P1.6... I have made this ckt and used two different MAX 232 ckts. The FP module ckt is working fine, bt again the GSM part is not transmitting any thing. There is no voltage on pin 3 of the DB9 connector(with is connected to the GSM module)...
Ny help???
Thanks
There is no need for optocoupler. U can directly connect relay through transistor. Make confirm whether your relay is working or not. Below circuit diagram will help for u and it will confirm whether relay is working or not through the LED which is connected across the relay.