operation of the home appliances is proposed. The telephone, acting as a remote controller, generates a DTMF signal corresponding to each dialed digit which is converted to a BCD code
by the Telephone interface circuit. This is given as input to the transmitter module which is then used to control various home appliances through a receiver module. Data processing stages of the transmitter and receiver modules have been implemented using digital components, thereby avoiding possible use of conventional devices like monostable multivibrators. Due to the fully
digital nature, the proposed design is less complex and hence the implementation is cost effective.
With the advancement in science and technology, human
beings have developed a tendency to make their everyday life amply luxurious with the aid of technology. This has led to the development of many sophisticated gadgets and equipments
that assist them partially/fully in their daily activities. Operating all such electronic/electrical instruments in a modern house might be difficult for the elderly as well as disabled people. Our primary motivation to build a simple and low cost system which remotely operates all the home appliances stems from
this point. We integrate our system with a standard telephone set so that the telephone can be used for the dual purpose of telephony and remote controller for various home appliances. The proposed system mainly consists of 3 modules, viz.,
telephone interface circuit, transmitter and receiver. The transmitter module is in turn made up of a digital data processing
block and a wireless (infrared) transmitter block and the
receiver module is made up of a wireless (infrared) receiver block, digital data processing block and a decoding block. In the scheme, a telephone receiver acts as a remote terminal
to provide input Dual-Tone Multi-Frequency (DTMF) signals
to the telephone interface circuit which converts them to
corresponding 4 bit Binary Coded Decimal (BCD) codes. The
transmitter generates an 8 bit frame using this BCD code to
facilitate asynchronous communication. The receiver decodes
the received signals after checking for any transmission errors (single bit) in the frame. These decoded bits act as control signals for the operation of home appliances.
The system employs an asynchronous type of communication
 in which the transmitter and receiver clocks are
independent. The receiver clock does not have any prior
information regarding the phase of the transmitter clock . This leads to the problem of choosing the correct sampling
instants at the receiver . Hence the data is transmitted in the form of frames instead of individual bits. Each such frame consists of start bits, information bits, and stop bits . This is explained in detail in the subsequent sections.
When the system is idle, the data processing block of
the transmitter gives constant logical high output. Since the transmitter consumes more power in transmitting logical high than logical low, the output of data processing block is negated before transmission to save power in the idle state. The
receiver module also senses this and remains idle whenever
the transmitter is transmitting continuous logical low. The
reception of a start bit changes the state of the receiver from an idle to an active state. It then has to sample the remaining data bits in the frame at proper sampling instants. Most of
the standard hardware schemes involve the use of monostable
multivibrators at the receiver to recover the data bits following the start bit. The monostable multivibrators commonly rely
on variable components such as resistance and capacitance
values, as well as they often account for a major part of
the propagation delays associated with the receiver. We have extended this treatment to a fully digital design that presents more challenging tasks including a digital...