A line following robot

We are building a line following robot. We need the robot to follow blue line with white background and blue line with black background. We made it by using LED and LDR to detect the light reflected from the sensors. The robot follows the blue line on white background using blue LED but and on the black background we are using blue and red LED to to detect the blue line but this doesn't work with white background with blue line. Is there way to use LED and LDR so that robot follows the line. We are going to race this robot against other robots so we don't want to use switch to turn off the red LED to make the robot work with white background.

I once had a line-follower robot kit (store-bought). As I recall it had only 2 photosensors, on either side of the line. The line had to be a darker color than the surroundings.

An op amp compared brightness levels from the two photosensors. It alternately sent power to the right or left drive wheel, depending on light hitting the sensors.

I did not test the robot with the line being lighter than the surroundings... But I don't think it would have worked. The two sensors knew how to handle only the one light/dark border situation.

I guess you have unpredictable situations?
So I believe you'll need three photosensors. The middle sensor will detect whether the line is a different color from the sensors.

The moving robot may have trouble initially acquiring a line. You may need to install some advanced logic.

try with color sensor or try the following links I hope it will be helpful for you.

https://www.societyofrobots.com/sensors_color.shtml

https://www.instructables.com/id/Build-your-own-attiny-colour-sensor/?ALLSTEPS

https://www.electronic-circuits-diagrams.com/sensorsimages/sensorsckt3.shtml

for blue black and white there is different voltage drop so check them with DMM and set the reference value for comparator IC

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and its better to use photo diode with white light