Comparator Circuit - Logic Low Problem

[Suraj143]

I am making an IR sensor based black line following circuit for my robot.

I use the below circuit.The circuit works but the logic low output will remain 1.7V which is quiet high the PIC will still detect as logic high.

How to overcome this?

 

[ronv]

The TL074 won't go to ground. Swap it out with an LM324 or LM358.

 

[ronsimpson]

The TL074 won't go to ground. Swap it out with an LM324 or LM358.

AND
You have a resistor+LED pulling up. It will help a little to reverse them (have the LED and resistor go to ground)

 

[audioguru]

Texas Instruments invented and make the TL074 and say its minimum power supply voltage is 7V (because its inputs do not work properly below +3.5V).
The datasheet shows that with the 1.5mA current of your LED its maximum output low voltage is about 3V (then the LED barely lights).
Why didn't you read the datasheet?

 

[Suraj143]

Ok thanks.I changed my IC to LM358 as well.Still no luck. But in computer simulator works fine.

The inverted pin voltage is 4.8V when measured.When the beam crosses from an obstacle the voltage drops to 4.63V.It has a 170mV to sense.Can it done by this LM358?

 

[audioguru]

THE DATASHEET SHOWS YOU WHAT IS WRONG. You did not read the datasheet for the LM358.
It says the Input Common-Mode Voltage Range is 0V to V+ MINUS 2V. The inputs MUST be +3V or less when the supply is +5V.

Set the reference voltage to +2.0V with the pot. Then the output will change when the opto-transistor conducts and causes the inverting input of the opamp to go below +1.99995V. With a 5V supply, the typical voltage gain of the opamp is 100,000.