Home appliance control by mobile phone (DTMF)
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The objective of this project is to enable users to remotely control their home appliances and systems using a cell phone-based interface. To access the control unit, the user should send an authentication code along with the required/desired function/action to his/her home control system via GSM. Upon being properly authenticated, the cell phone-based interface at home (control unit) would relay the commands to a microcontroller that would perform the required function/action.
1.2 Problem Statement
The objective of this project is to develop a device that allows for a user to remotely control and monitor multiple home appliances using a cellular phone. This system will be a powerful and flexible tool that will offer this service at any time, and from anywhere with the constraints of the technologies being applied. Possible target appliances include (but are not limited to) climate control systems, security systems, and lights; anything with an electrical interface.
The proposed approach for designing this system is to implement a microcontroller-based control module that receives its instructions and commands from a cellular phone over the GSM network. The microcontroller then will carry out the issued commands. For security purposes, a means of identification and user authentication will be implemented, and will combine caller identification with a password authorization.
1.3 Operating Environment
The control system will include two separate units: the cellular phone, and the control unit. There will therefore be two operating environments. The cellular phone will operate indoors and outdoors whereas the control unit will operate indoors.
The following is a list of assumptions for the project:
1. The user and control unit will establish communication via GSM.
2. All service charges from service provider apply.
3. The controlled appliances will have to have an electrical interface in order to be controlled by microcontroller.
2.1 Review of related literature:
This project has been made by several people, but most of the times a land line phone is being used. If a land line phone is used than a separate ring detector circuit is required for detecting the number of rings and then picking up the phone. It uses an extra relay and we have to enter inside the mechanism of phone.
In our project we have used the auto answer facility which is present in many of the cell phones today, so we escaped from designing the ring detector circuit.
2.2 Present Scenario:
Possible customers for this product would be home improvement contractors, and supply stores. The benefit of this is the end-product can be sold in large quantities and it can be incorporated into the construction of modernize homes. The end-product will be not be sold in retails stores because reconfiguring of the end-product to control different electrical appliances will be complicated and it should only be attempted by trained technicians. Retail stores would also not be a good target for commercialization due to the system requiring a cellular phone plan in order to operate. Advertising through cellular phone providers would be a more feasible option.
2.3. Present and Future Scope:
This product is aimed toward average consumers who wish to control household appliances remotely from their cell phones provided that the appliances are electrically controllable. Example of feasible appliances and applications under consideration include; enable/disable security systems, fans, lights, kitchen appliances, and heating/ventilation/air conditioning system.
Right now we have designed the project for control of two devices but it can be designed for more number of devices.It can be furthur expanded with a voice interactive system facility. A feedback system can also be included which provides the state of a device(whether it is on/off) to the remote user.
3.1 System Specifications:
1. An authenticated user can control two home appliances from any remote place having mobile phone network.
2. Regulated power supply: 5V and 500ma.
3. Relay: 230v AC
4. The system requires two phones out of which the one present at the control unit has to be a cell phone with auto answer facility.
3.2 Block Diagram Description:
Phone on the transmitting side:
The person who wants to switch on/off any device kept at the controller side calls from a phone and, once the call gets picked up, enters the password and tones for a corresponding device. Every key has to be pressed for a minimum amount of time to get it latched at the decoder IC.
Mobile phone on the receiving side:
The mobile phone on the receiver side picks up the phone automatically after 5seconds, and then makes the tones available to the DTMF tone decoder IC through the headphone jack of the phone.
DTMF Tone Decoder IC:
The DTMF tone decoder IC converts the received tones to their respective binary values and then gives them as an input to the microcontroller.
The DTMF tone decoder IC’s internal architecture consists of a band split filter section which separates the low and the high tone of the received tone pair, followed by a digital decode(counting) section which verifies both the frequency and duration of the received tones before passing resultant 4-bit code to the output bus. These 4-bits along with a bit which validates a received tone are given as an input to the port1 of microcontroller.
The five output bits of the decoder IC serve as an input to port 1 of the microcontroller. Then each tone is verified by the programmed microcontroller and once a correct sequence of code is received, output corresponding to the tones sent by the user is made available at the port0, which is connected to relay through a relay driver.
The output from the port0 of the microcontroller is given to the relay driver IC which drives the corresponding relay, to which the home appliances are connected.
One terminal of each appliance is connected to relay and the other terminal is connected to 230v AC. As soon as the relay gets driven by the microcontroller the device gets switched on/off.
3.3 COMPLEXTIES INVOLVED
Under this heading we are going to mention the problems that we faced while building this project:
1. Building a programmer for the microcontroller: There are several kind of microcontroller IC’s available in the market. We first bought Intel’s 8051 IC, but found out that it does not have flash memory, so we were not able to use it. Then we bought Atmel’s AT89s52 and tried to build a programmer circuit for the same. After investing some time on finding a programmer, we learnt that AT89s52 supports In System Programming (ISP) and can be programmed through the parallel port of a PC. Then we found out that a software named AEC_ISP can be used to program our IC. So we built a programmer circuit whose schematic was their inside the software and were successfully able to program our IC.
2. PCB printing: For getting a printed PCB for our circuit we first needed to design a layout. We learnt that in a software named ‘DIPTRACE’ we can draw a schematic of a circuit and then get its layout. So we learnt this software and printed a layout of correct scale to actual components. Learning the software was a complex task.
3. Programming the microcontroller: We programmed the microcontroller many a times and tested it, until we got the final result.