A simple capacitive security card system

A simple and reliable capacitive security card system is designed, fabricated and tested. It consists of capacitive card reader system, an integrator, rectifying circuit, an 8051 microcontroller and LED indicators. Initially rectangular patterns of different lengths are being recognized successfully. The patterns on the security card are scanned with a thin conducting plate, which is the part of the reading system, when card is inserted in the reading system. The variations in the heights of the patterns are being converted into voltages with the help of an integrator. Output of the integrator, after rectification, is converted to digital form and fed to the microcontroller. These data are compared with the data stored in the memory of the microcontroller. The designed system is capable of recognizing up to five columns (patterns) in a single row with a maximum number of 99999.