· Micro-controller based telephone Answering Machine.

ABSTRACT:

The aim of this project is to build a simple telephone answering machine that is controlled by a micro-controller. The system is developed using the 8051 micro-controller as CPU, inbuilt flash memory, an IC (APR9600) to record and playback voice and relays.

The working of this answering machine is very similar to that of any other classical answering machine. When the telephone is not picked up after a specified number of rings, the control is transferred to the answering machine that performs the following functions:

· The call is taken - the phone line is in the off-hook state.
· A recorded message is played back informing the caller to leave a message.
· The caller's message is recorded.
· The telephone line is disconnected.

The various components of this system are:
· Ring-detector circuit
· Relay circuit for taking the call and disconnecting the same
· A voice recording and playback circuit

The functioning of the various parts of the system are given below:

The system uses a monostable flip-flop as the ring detector circuit to detect incoming calls. After a pre-defined time delay, if the handset of the phone is not picked, the answering machine circuit takes over. The monostable circuit's output is given to the micro-controller and if it detects an on-hook state after the delay, the micro-controller triggers a relay that releases the hook switch in order to simulate the off-hook state.

Then a message is played to the caller asking him/her to leave his message. The message record/playback of the voice recording IC is controlled by the micro-controller. Programming the m-controller via the ports lets the user playback and record messages through the APR9600. The caller's message is then recorded using the voice recording IC. After the message has been recorded, the hook switch is released by the relays.

The ring detector circuit meanwhile continuously monitors the arrival of any incoming call and the micro-controller transfers control to the answering machine circuit via the relays if the need arises.

· Study of Wavelet Transforms For De-noising Applications:

ABSTACT:

One major advantage afforded by wavelets is the ability to perform local analysis. Wavelet analysis is capable of revealing aspects of data that other signal analysis techniques miss, aspects like trends, breakdown points, discontinuities in higher derivatives, and self-similarity. Furthermore, because it affords a different view of data than those presented by traditional techniques, wavelet analysis can often compress or de-noise a signal without appreciable degradation. This project aims at comparing the performances of the different wavelets used: Daubechies wavelets, Symlet wavelets, coiflet wavelets, Haar wavelet, Bi-orthogonal wavelet and Meyer wavelet. The criterion for performance comparison is the mean square error obtained after de-noising the image.

· Wireless LAN Standard 802.11b

As a part of a summer project, I implemented the modulation schemes used in the standard for wireless LANs 802.11b. This SIMULINK implementation was focused on the modulation schemes Packet Binary Convolution Coding and Complementary Code Keying. These two modulation techniques are of immense importance as they have made available two transmission rates namely, 5.5 and 11 Mbps.