DTMF Controlled Home Automation System: In this project, we have designed a system that is able to control electrical appliances wirelessly with the help of a mobile phone. The automation system basically reads different frequencies from a mobile phone keypad and those different frequencies are then decoded and then used to control different electrical equipment’s attached.
The frequency generated from the mobile’s keypad is fed into a decoder which then decodes the frequency and generates an output which is then driven into the base of a transistor. This turns on the transistor and the electrical appliances attached to it! Each keypad generates a different frequency which then simultaneously turns on the component depending on the value decoded.
The approach was divided into 3 phases. Firstly, we accurately read the frequencies from the keypad of a mobile phone. This was done by connecting the mobile phone with an AUX cable and feeding the signals from the cable into the decoder. Secondly, we used the Dual Tone Multiple Frequency (DTMF) decoder to convert the frequencies we got from the mobile phone into the base of the BJTs. Thirdly, we used the BJTS to run the appliances connected according to what frequency was provided to us as input.
The major issue that was faced was with the IC ULN2003A. The outputs of this IC were connected to the three relays that were used to control the appliances. The output of this IC turned out to be quite low on receiving the signal. So we replaced this part of the circuit with the transistors and connected the LEDS,Fan and buzzer to the collector of these transistors.
We learned that different frequencies generated by the mobile key pad can be used very conveniently to control switches using a DTMF. We used NPN transistor to make a switching circuit. This Model can be applied on a larger scale to operate devices which require 220V AC supply. This model can further be improved by using a Bluetooth or Wifi module to transmit dial tone frequencies wirelessly to the decoder.
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