Raspberry Pi Forums

Hello everyone,
I am new to the raspberry world, I want to make a project where I can control LEDs with a 4-channel relay either to turn them on or off. the user will have the choice to control these LEDs either through SIM800L GSM module or through wi-fi from an android application. the raspberry pi will be working as an access point so that the user can connect with it and give commands through wi-fi. so guys I want to know if it's possible to control them by two methods at the same time. and what are the steps to do that.

I am certain there are experts better qualified than I on here, but here's my two penneth...

yes, this will work, and the Pi can be set to control both at the same time. However, your spec is vague at this point. If you want the Pi to power 4 GPIO pins (high or low) that in turn switch a relay contact - then I would use the output of the Pi GPIO into a transistor switch with a limiting resistor then in turn triggers the relay to switch on or off. if you use this method, you can simply amend the circuit to power two relays via the same transistor switch.

Plenty of circuit diagrams and explanations on the net. But yes, this is possible.

the user will have the choice to control these LEDs either through SIM800L GSM module

It is not a limitation of the RPi or your GSM module, but I understand that some cellular network service providers do not handle 'inbound' data calls to subscriber devices.

So if you were thinking that a cellphone user could 'browse' to your RPi with a web connection and change the state of the relays that is a detail you should check with your cell network provider.