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HELP:Line Follower Robot

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sambhav:
hi...

I am doing a project...Its a robot and 1 of its missions is a Line follower. it follows a black line on a white surface.. this is done by using 2 IR reflective sensors (TCRT9000) at the bottom very close 2 surface.
The Ckt is very simple.
The outputs go low when the LED/IR Detector pair is
positioned over a black surface and high when positioned over a white surface.These outputs r given to the microcontroller.

But the problem we r facing is that the o/ps of the sensors is very low.
when on black surface, we got around 20mv(should be ideally zero). however on a white surface the o/p we got was around 150 mv(ideally should have been equal to supply voltage i.e. 5v).
So we cannot give these directly to the microcontroller. what can be the problem..??how do we separate the two levels..??
Also,.. would changing the sensors solve the problem..?? if yes.. can u suggest any other IR sensors which cud b used..??

Thank you.

Admin:
just for reference:
http://www.societyofrobots.com/schematics_infraredemitdet.shtml

what resistor values are you using? i think you just need to increase the resistor (that is in series with your IR sensor) to 10kohms+

Militoy:
Your 20mV level should already be interpreted as a logic 0 (low) - and you may well get an acceptable "high" level by changing your resistor value - but ideally, to get a good active logic low (or high) interface from a reflective IR sensor, its output should be buffered using an op-amp. Here is a link to the application notes for the sensor you're using - even if you're not able to make use of their performance charts, looking over the application circuits should help you.

http://www.datasheetarchive.com/search.php?q=TCRT9000&sType=part

(Click on the icon under "Information" for the data sheet)

sambhav:
The resistor values i m using is 180ohm in series with IR Tx. and 15k ohms in series with the receiver and 5v supply. do i still need to increase it..??

Admin:
hmmmm interesting . . . since the voltage out seems to be low, probably means that the sensor isnt getting enough light.

ok a few things to try:

1) shine a bright light on the sensor and see how how the value goes up . . .

2) make sure the infrared LED is connected properly - they are bipolar, so the long end needs to be connected to the 5V (stupid check :P)

3) what kind of black line do you have? just because it is black in visible light doesnt mean it is black in IR. in the datasheet, read page 4 where it talks about 'Black on white paper.' Drawing ink will cause the results you have just described. try different black objects and see what happens. (for example, in IR, snow is black.)

4) theres a small chance the IR emitter is broken - cover up just the emitter with black electrical tape and check the voltage output

5) try a 50kohm resistor and check the outputs

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