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help me for sensor circuit for lone follower

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hai, i made a sensor circuit for line follower using lm324 comparator,i have a lot question about it,plz expalin it, i attached diagram of comparartor circuit, i want a maximum output (4to 4.5),pin 3 i put high resistance,the output is 3.7 without turn on the led(D1), D2 is LDR, if i turn on D1 the comparator output doesnot chang(only vary 3.7 to 3.6), what is the working condition of ldr in this circuit? otherwise plz explain the working condition of this circuit.plz


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New Member
huy pavithrams,

apparantly you are providing 2.5 volts to D2, are you sure it works fine at that value? looking at the circuit diagram that you've provided, i'm quite doubtful whether it is an LDR because it doesn't appear to be a resistance! i think you are using a solid state detector. they are phototransistor or some such king of stuff. if this is the case then you must check if it works after changing the bias i.e. invert the flow of current through it! maybe its a pnp device which you may be treating as an npn or vice versa!

what is the gain of the amplifier which you are using as the comparator? you can set the gain to a higher value to get a better variation in output voltage!

you can also use R6 to calibrate the difference value, i.e. you can turn the LED off and then vary the resistance of R6 to bring a zero at the output.

i think you are getting a 3.6V even LED is off, you must set this to zero through R6. after that you must change the gain to some other value, perhaps 45 times the current value because you said that the value changes from 3.6 to 3.7. this means the opAmp is giving a difference of 0.1 in the outputs. after you bring the initial value to zero volts (through R6) you must get a 0.1V with LEd turned on! by setting the gain to 45 times the current value, you can get 0.1Vx45 = 4.5V at output!

you can also put another transistor directly after the D2, i.e. between the pin2 of LM34 and the sensor, to make a darlington pair, which can greatly enhance the results. just google darlington pair if you aren't already familiar with the name. darlingtons are simple to implement...

hope it proves helpful! :)
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