Photosensing circuit problem

[reko]

Hello everyone i have been working on a robot that follows a line and had a problem with getting a sensor to work with so i had to lookup designs on the web and found one

my problem here is that i don't understand the concept or got it wrong cause i am installing the parts right now and have a big time problem wheather to put the photo diodes under or both the photo diodes and the iRLEDs under the body in order for them to both send light signal and recieve it via the diode please tell me what i should do ASAP nad if there is an alternative please tell me about it

View attachment 39801

 

[audioguru2]

The photo-transistor turns on when it sees strong IR light relected off white floor or a white line on dark floor. Then the opamp's output goes high and the LED turns off.

Both the IR LEDs and the photo-transistors should be mounted on the bottom, shining on the floor and be shielded so that IR from the IR LED can't shine directly on the photo-transistor.

 

[reko]

thanks very much man i am using a photodiode insted of the photo transistor (LDA) is it ok?

 

[audioguru2]

Your circuit shows and is designed for a photo-transistor.

You will need to change the input resistors to 100k or 1M (try both) for photo-diodes.
Then the photo-diodes need to have their anodes to ground so that they are reverse-biased.
What is a LDA? An LDR is different from a photo-transistor and different from a photo-diode.

 

[reko]

LDR like in photo resistors sorry for the mistake anyway am a newbie as you see so thanks for every thing and i didn't get the reason for increasing the resistance and what did u mean it should be connected to GND it's already one input with the 10k R and the other is to GND

 

[audioguru2]

The load resistance for the photo-diode must be a higher value than for a photo-transistor because a photo-transistor amplifies the photo-current and the photo-diode doesn't amplify.
Here is how it should be wired:

View attachment 39804

 

[reko]

thanks man u really rock