As shown in Fig. 1, Arduino Board 1 and GSM module get ground connection through transistor TIP142 (T1). Also, very little drive current (<5mA) is required from Board 1. A 12V, 2A regulated power supply is recommended. It should be able to deliver 2A of current for the GSM module. An optional battery backup system can be added for additional security in case the burglar decides to turn off the electricity.
House the circuit in a plastic box and place it in a locked wooden cabinet. Make sure the GSM module has good signal strength. The alarm system can also be used to protect warehouses, shops, banks and office buildings.
Software is written in Arduino programming languange. Arduino Uno Board 1 and Board 2 are programmed using Arduino IDE software. Atmega328P on Arduino Uno comes with a pre-programmed bootloader that allows you to upload a new code to it without using an external hardware programmer.
Connect both Arduino boards one by one to the PC and select the correct COM port in Arduino IDE. Compile the program (sketch). Then, select the correct board from Tools→Board menu in Arduino IDE and upload the sketch.
Arduino1.ino sketch is at the heart of the alarm system and carries out all major functions of the circuit. Arduino2.ino sketch is used to reset Board 1 and GSM module by switching off the power for a few seconds via T1. Please refer to source codes for details.
The author’s prototype is shown in Fig. 4.
Download source code
Joy Mukherji is an electronics hobbyist and a small business owner in New York, USA, and Lucknow, India. His interests include designing radio-frequency circuits