[SOLVED] Circuit design help........................................

[kdg007]

this the circuit i built (transmitter and receiver)for my project,As you can see i kept 1 white LED.Instead of the voltage at R1,i kept frequency generator to give square wave.
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the above picture is the waveform from the lm339 comparator when i used only 1 LED with the single transistor.
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this is the waveform i got from using 1 LED,the signal is not proper.y is it so ? am i missing something ?
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any suggestions would help.thanks

 

[emresel]

Actually i can't understand your question. What is photo1 and photo2? What s the first signal (in photo1 upper signal) and the bottom one?

 

[FvM]

To check for correct operation of your driver circuit, you would preferably measure signals from the driver itself as a fisrt step, e.g. voltage across R7.

A weakness of your darlington driver is the lack of a base-emitter resistor for Q2. A sufficient low ohmic resistor (e.g. 100 ohm) helps to switch of Q2 fast. The square wave frequency can't be seen rom your waveform, so it's impossible to guess if Q7 switching speed matters.

I also think that the photodiode cicruit isn't well designed. The shorted comparator output is just a drawing error, I presume. Operating the photodiode fowward biased is the least sensitive of possible photodiode circuits and also affected by temperature drift.

 

[kdg007]

i redesigned the receiver circuit again.. you are right,there is a mistake according to the calculations.I kept 100k instead 1M..now its working fine.had to tune the input terminals properly .thanks