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line following robot

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hi friends,
i am planning to do a line following robot as my final year project.
i thought of using infrared sensors , because i heard that phototransistors won't work well in daylight. could you please send the circuits and also about placing of sensors.also tell me what kind of strip will reflect IR rays. waiting for your suggestions.



New Member
Phototransistors for the visible spectrum will be messed up by daylight unless you put something around it to block out the light. IR sensors can be messed up a little by daylight, though they are not as prone. If you were to modulate an IR signal to be reflected from the surface that would eliminate most any interference.

It's hard to say exactly what reflects IR and what doesn't, it's often about the same as the visible spectrum, ie white objects reflect it and black absorbs it, but you can set up a test circuit with an IR led and sensor to see how much it actually reflects.


Phototransistor are affected by day light, but you can easily create a small window or tube to prevent stray light from entering your detector except from the ground. You can also modulate your IR light source so that you can then bandpass your frequency and prevent the stray light at other frequencies from affecting your measurement.


New Member
You can use the CNY-70 sensor

it is an integrated infrared diode with a photo transistor. The receiver has a small optic filter (lent).

I used them for bilding a line follower and it worked perfectly. The only thing is that you must have a potenciometer for regulating the compare point because of the enviormental light. Anyway this sensor is mounted with a small plastic protection so it is no so critic.

Anyway, if you want to avoid problems with light in a 100% you can transmit a modulated signal of some KHz (the PIC can do it alone, you don't need an external modulator) and than use a filter for detecting the KHz signal (a simple first order filter with an Operational Amplifier should be enought). This mechanism allows you to avoid perfectly the external light because it is only a DC offset.


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