At first, let me give a brief introduction about relay to you.
Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal. It acts as a “low voltage controlled switch to control high voltage”, For example, if you want to control power of your washer or air conditioner, which is oftern110v or 220v,by microchip, such as AVR or PIC, it is necessary and safe the make your microchip control the relay first, and then control the power supply of those device with the relay.
With the GSM SMS, it is possible to control the relay remotely. You can send a message via phone to control the relay on&off. With this, it will convenient to control any device wirelessly, especially helpfully on irrigation, smart home, outdoor remote control etc.
So, let’s make such a “SMS control relay” with Arduino, GPRS/GSM and a Relay module.
Step 1: Prepare your tools and parts.
Device Max current(A)
Electric Fan 1
Microwave Oven 8
Air Conditioner Depends on the power, usually <20
The modules I used in this application are as below:
Elecrow GPRS/GSM Shield
Elecrow Relay Shield