Electronic Identification and Personal Information card using 8951 Microcontroller

WORKING

Card: – We can divide the cord in three major parts one receiving section, two processing section, three transmitting section. The receiving section receives the data & send to processing unit decides about the output for received data, now the output data sent to the transmitting section.

Receiving section: – In this section we are use IR sensor 1738 which detects the infra red light of switching rate 38Khz, as it detects this light its output gets low or we can say that its O/P is active low. The output of 1738 switches between TTL leaves (5V or 0V) according to the condition of the light incidenting on the sensor.

Although the O/P voltage level of 1738 follows the TTL logic but it cannot sink or source much current so we need an amplifier with higher input impedance to reduce the current drawn from 1738. Hence we use first BC548B connected with 1738’s O/P in common collector configuration which amplifies the sourcing current now to produce high sinking current we cascade this stage with another BC548B working in CE (common emitter) configuration which produce an output signal of high sourcing & sinking capacity but because of its characteristics it inverts the I/P signal. Hence to convert the signal in to its original form we again use the same ckt. cascaded with previous one, produces O/P same as it comes from sensors (1738).

Now this serial data is applied at the pin no. 10 of the microcontroller from this pin microcontroller reads the data, test for the condition using software & send the output (serial output) at pin no.11, flow chart shows the structure of the software we developed.

Here we see that some other components are connected with microcontroller there function are explained below.

12MHZ X-tal, microcontroller requires this produce the 12 MHz clock for the functioning of micro controller the two 33 pF capacitors supports the OSC. ckt.

Pin 40 of the micro controller is positive supply pin hence connected with +5V,

Pin 20 is grounded.

Pin 9 of micro controller is use to reset the micro controller the capacitor (10?F) & resistor (10K) network connected at this pin provide the switch on reset to micro controller to avoid mail functioning of unit when switched on or on battery replacement. One push to on switch is also provided to manually reset the micro controller.

Transmitting Section: – as we know that sensors only detects 38 KHz IR signal so we modulate the 38KHz signal by microcontroller’s O/P bit stream the combination of these two produces the bursts of 38Khz.

To perform this we use IC555 in astable mode & components are selected such that it produces a 38KHz pulse train of duty cycle 25%.

The ckt. works as the charging of capacitor (which decide the on time) is done by the 1K resistor & 6.8K resistor although another resistor of 22K is connected but due to the diode connected in series with this resistor, it does not affects in charging because during charging diode gets reverse biased so behave as open circuit. During the discharging of capacitor the 6.8K resistors gets disconnected from the ckt. due to the reverse biasing of diode connected with this resistor.

Now to modulate these pulses we apply the modulating signal at the pin 4 of IC this pin is used to reset the IC hence when ever we apply a low pulse at this pin the IC’s O/P immediately switch to low state & remain at that state until the pulse does not changes its state.

As we know that sensor O/p is active low hence we send the bursts for ‘0’ logic but the insertion of zero logic at pin 4 of IC will reset it hence we apply the signal at pin 4 after inverting the signal through transistor BC548B.

PC Unit: – The transmitting & receiving unit of this section work in same way as in card but here we use the PC to show the details.

In our project we are using the serial port to communicate with PC & as we know that on serial communication mode it uses the RS232 standard for which logic 1 is assigned to a voltage less than –3V & logic 0 to greater than +3V because Rx.,Tx. Sections & microcontroller provides the O/P at TTL level, we use here MAX232 as level converter which have two TTL to RS232 converter & two RS232 to TTL converter hence the O/P of serial port available at pin3 is applied to one of the two RS232 to TTL converter & I/P to serial port is fed through TTL to RS232 converter.

Applications

1. This card can be used for ATM, Credit Card, Driving License etc.
2. Automatic Doors.
3. Attendance Counting.
4. Security System.
5. Infra Red Data Exchanging.
6. Reservation systems with railways & airways.
7. For sending important data through Card.

Limitation

1. It requires a battery source.
2. A separate Infra Red Card reader required.

Future Enhancement

1. We can replace the devices with SMD, which will reduce the size of card.
2. We can use photocells to dispense with battery source.
3. We can store images for identification of card holders.

References

1. Micro Processor Architecture by Ramesh S. Gaonkar .
2. Op Amp by Gaikwad.
3. Micro controller by K. J. Ayala.
4. Integrated Electronics by Millman & Hawlkiwas.