Wireless Data Encryption
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Joined: Apr 2010
29-05-2010, 12:03 AM
in this project and implimentation need to designe a circuit which contains a micro controller which Sends the serial data through its serial port every time after resetting. Then it sends the data by RF using DTMF tones.
Now after transmitting the data micro controller wait for some time and then again transmit it.
Information transmission by IR:-
These informationâ„¢s are pre feeded into the microconrollers ROM and by using infrared LED in the following way :-
As we know that sensors only detects 38 KHz IR signal so we modulate the 38KHz signal by microcontrollerâ„¢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 ICâ„¢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 Ëœ0â„¢ 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.
Reception of IR data:-
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 1738â„¢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 to the MAX232 because serial port of pc which follows the RS232 standard hence we use a Level Converter between port and Buffer Amp.
The level converter converts the TTL signals in to RS232 signals.
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