Digital Temperature Sensor
We used LM35 analog temperature sensor which provides change on voltage level for change on temperature. Arduino analog input pin convert the analog voltage to digital value using its internal ADC.
We used MQ-135 gas sensor as somke detector. Digital pin will provide digital output in case of smoke detection.
SIM900 GSM Module
SIM900 GSM module communicate with the system via SMS from user. GSM module connected with Arduino using software serial interface. Check the below reference for interfacing GSM module with Arduino.
Below circuit shows 2 separate power supply unit for Arduino and GSM module to make sure each module get enough current. 4 Line LCD connectivity is same as 2 line LCD connectivity. Temperature sensor conected with analog input pin and smoke sensor connected with digital input pin. Red LED indicate the alarm status.
8 volt rechargeable battery is connected with the power supply to run the system in case of power failure.
Please check the below video tutorial for details