The ËœOnline Device Controller (ODC) is a multi-channel hardware administration
system that has been developed to enable the control of equipments and appliances from
any part of the world, through the Internet. The concept of ODC is a relatively new one,
and makes use of Common Gateway interface (CGI), a very powerful technique that was
hitherto used solely for e-mail, database access and other Ëœsoftâ„¢ purposes involving
dynamic web page content. But, through this project we have made an attempt to bring a
very powerful but often unknown and underutilised aspect of CGI; the same technique
used to manipulate our e-mail accounts can equally well be applied to access the parallel
port of the web server, and control hardware through it.
Our project, the ËœOnline Device Controllerâ„¢ allows a remote user to login to the
Web server and control the devices connected to the server. Also provided is the feature
to control the same devices locally, through a Cordless Telephone.
The present product offers the facility to remotely control an ON/OFF device and
an Intensity Variable load, through the Internet, and locally through a Cordless telephone
and is a product of paramount significance in office, industrial and household
Working of the System
A typical scheme of the working of the system can be described as follows.
A remote user can log in from any location in the world to the homepage of the
Web server through the Internet/Intranet via a Web Browser. This request is processed by
the CGI and after security check, the user is presented with the current status of
equipments. Now he can control the equipments as required and he can send the
information through a form or menu. According to the control information received, the
CGI executes the required programs to read/write data to the parallel port (LPT1).
Local control is made possible with a Cordless telephone. The PC and phone
produces their own interrupts. When a key on the keypad is pressed, the arrival of a new
valid DTMF tone will interrupt the PC using the PC Parallel port (using IRQ 7). The
DTMF tone generated from the telephone line is decoded by the DTMF Decoder which
produces the corresponding 4 bit BCD code output which is read by the Microcontroller.
The Microcontroller 89C51 reads the appropriate control signal when interrupted by the
PC (through /INT0 pin of the Microcontroller). This is processed and is sent to the output
port, and to the devices. ON/OFF devices are controlled through the Relay Based Control
circuit and Intensity Variable Loads are controlled via the Triac Based Circuit. The firing
pulse for the Triac is generated by the 8951. To synchronize the firing pulse with the AC
cycle, a Zero Crossing Detector circuit is also used which is connected to another
interrupt pin (/INT1) of the Microcontroller.
After executing the control signals, the actual status of the equipments are read by
sensing the load current by means of a Current Transformer, is fed back through Status
Reading circuit and is read through the input pins of the PC Parallel Port.
Finally, the remote user will receive back the confirmation message that the status
of the devices has been changed as per the control signal sent by him. This completes the
cycle of events.
Full project report download: