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Some issues in data transfer using light.need help

4 593
dimonga  

1.Transmitter

The basic stages of transmitter are as follows:
USART(serial data) --> FSK modulator-->Led fast switching circuit

The switching circuit is working fine and i have transmitted and received data successfully without modulation.But now i need to add some digital modulation

The issue is that  if i send serial data to LED then there is visible blinking of LED but since i need no flickering therefore i have thought of using the modulation stage to remove the blinking but the problem is that whlie desiging FSK modulator there are 2 methods  have tried

A) Using 555 IC as shown below, but the circuit is not providing the desired frequency also the circuit becomes complex so does the demodulator, so i have discarded this method



B) USING Softmodem in Arduino.

I have tried using arduino as modulator by following the steps as shown on http://learn.linksprite.com/ardu ... ta-communication-a/  but using this modem ,there is still flickering of LEDs when fed to switching circuit.


There is another way to use XR-2206 ic for desiging FSK modulator but it is not available in my region.

What should be done to use FSK modulation in the circuit. Or suggest some another digital modulation technique (note that the message and carrier signal both needs to be digital).

Thanks in advance.


12458  
Why not just wire up a NOT gate and MOSFET driver with a MOSFET. Just set the UART speed high enough so the eye cannot see the flicker. Then at the receiver receive the light signal and use a NOT gate to invert it

12458  
Also why modulation?

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