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Thread: Line follower sensors

  1. #11
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    For the last two, the robot has to turn to the turn, so there is no ambiguity.
    turn how much?? You are using PD controller!! if you turn the same degree, why do u need a PD controller??

    You DONT need a controller or a PD algorithm if you dont care about the ambiguities. You dont them either if you are using TWO sensors, that too to the edges. You can just use two transistors!!! and yes, you can use a couple of OP amps for a differentiator!!!

    having said this, i would like to know , for the info, these:

    1) the type of sensors used
    2) the type of emitters used
    3) the modulation technique used
    .... I didnt do it ! ....

  2. #12

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    does it give good analog value?? like the area in which receiver is active is quite low, so to use that analog value as amount of error is doubtful...

    as in at one point the error is 1% and within 3mm of a distance it is 100%!!

    I think i should try this out but,,
    give me some more detail about this linefollower please...

    you know keeping a sensor array works very fine, and we know where exactly we are...but if we can apply this logic also in sensor array theory then it will be nice!

  3. #13
    Super Moderator T-1000 docel's Avatar
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    2 sensors....and you need an algorithm??
    and PD???
    Meaning , Microcontroller(s), maybe????
    :lol: :lol: :lol:

    Boy! I'd love to see the 'speed' of that thing....

    Kartikmohta, I think you are just passing time. I do'nt think you have any genuine problem but just want to show off your theoretical knowledge, scourged from the net here and there. The more you say , the more ridiculous you seem.

    You ask something and answer it yourself , with a twist of contradiction to your own ideas. Then you reply that you have already done it. Tomorrow, you'll probably say it won prizes already!
    What are you up to?

    Your problem of the thread is absolute nonsense!

    I suggest that you take time out and concentrate on your studies. Get back here after exams, after you read your own posts in detail, with a free mind.

    Now, I would like to see some 'meaningful' and relevant posts here. Some of the things you say make no sense, and its confusing to people who are just starting. i cannot allow that to continue. You're welcome to a healthy discussion, but enough is enough. Good luck!
    docel
    ^Anything is possible..
    after YOU prove it!!

    http://bangalorerobotics.tripod.com

  4. #14

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    Perhaps this is what Kartik has been trying to suggest...

    http://www.me.iitb.ac.in/~adeshmukh/linefollower.php <Check the video at the bottom>

    Uses the same two sensors - analog value setup with P control as mentioned.

    By "diffused" light, I SUPPOSE Kartik was trying to suggest that you DONT align the emitter and receiver to get maximum reflected voltage but deliberately keep them parallel so that the voltages received give a more linear (only relatively speaking) response, kind of like decreasing the sensitivity of the sensor setup so that direct reflection doesnt overwhelm the receiver. This COULD give analog values that MAYBE can be used for PD control.

    Just my interpretation of whats been going on the forum last few days.

  5. #15
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    yes, pppp, we got the idea alright!!

    But the counter argument was that there are issues to this method!!

    putting it in a simple way -

    we humans have the most sophisticated control systems, i guess. Looking at both sides of the argument -


    *> We see because light gets reflected from the thing we see.

    *> Reflected light is like a torch light pointed out to the thing we want to see - minimum power, and we see only what we want to see. - the line

    *> we feel comfortable with a tubelight illuminating a room, but we dont have to see the minor details - we are just looking for a line!! This situation is ideal when we use a camera for image processing . But a tube light requires much more power than a torch light!!

    *> so we dont have to use a tube light when a torch would do the trick.

    *> try illuminating the whole room with a torch light!! compare this with focusing our target with the torch light!!!

    no more arguments from me on this thread!!!



    :twisted:
    .... I didnt do it ! ....

  6. #16

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    i really dont know, whether we will get good analog output or not, ... but i think i should try this out,

    because the receiver works on an area (it has a lens) so if we get good analog value then that value will give us the 'amount of line' inside the circular area in which the receiver is active...

    and of course, amol bhaiyya has tried it, then there has to be some point in it!

    Man! lot many things to work on!!!

  7. #17

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    @allbits: I guess you got the analogy wrong. A better analogy would be a bright torch with a small beam angle (for the conventional reflective multi-sensor array) and a dim torch with a large beam angle (for the analog sensor design).

    A bright torch with a small beam angle would illuminate the object of interest very nicely. But what will you see when you point the torch slightly away from the object? Nothing ... Darkness. Imagine navigating in a dark room and trying to maintain a predefined path (say by following a line). A slight misalignment of the torchlight leads to a complete loss of information about the direction of the line. Now imagine the same situation with a dim torch but with a larger beam angle. Slight misalignments still show you the line and allow time for correcting your path.

    Now I hope its kind of trivial to judge whose 'speed' can be higher :P. As far as the use of microcontrollers is concerned, I don't think it is essential to use them as a PD algorithm can be easily implemented using opamps.

    As for the range of analog values that one can obtain from it, take it from me that the values are high enough for detection. And yes from first-hand experience, the speed of a PD-controlled line-follower can be much higher than that shown in the video link posted by pppp

  8. #18
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    @allbits: I guess you got the analogy wrong. A better analogy would be a bright torch with a small beam angle (for the conventional reflective multi-sensor array) and a dim torch with a large beam angle (for the analog sensor design).
    better?? than what?
    There was no argument on "analogy" in this thread!! and you are the first one to bring in the word "beam angle" (which, I guess, you are meaning something like the "radiation pattern" rather than the angle of beam to the object) - And i never said you were wrong, - since this is your first post!!


    But what will you see when you point the torch slightly away from the object? Nothing
    yes!! that is the point!! you should not see the object when you point it away!!! that is, you should not see the LINE when the light is NOT illuminating the line!!

    A slight misalignment of the torchlight leads to a complete loss of
    information about the direction of the line.
    Yes, it will, but this is the trade off, and the cost you pay for better demarcation.

    I Understand your point something similar to this - A torch in the dark room will let you see only the thing you point the torch at, and if you point the torch wrong, you may not see what you are looking for.

    Where as, a bulb will illuminate the whole room, so that you can see the object even if you are not pointing at it.

    But then, the sensors are not intelligent -

    1) Comparing the methods, you can easily see that the bulb needs to be more powerful (in terms of total light radiated) than the torch, or the sensor needs to be more sensitive.

    2) The confusion was all about "diffused light", and the OP failed to give an convincing explanation of the word "diffused" as he used it. Any waves reaching the sensor are reflected waves. Any waves reaching the sensor, not getting reflected from the line is useless to us.

    3) The thread was NOT about illumination, it was about getting distance value using 2 sensors - whose solutions has illumination issues as part of it.

    The motive of this thread was NOT to have a good discussion on light effects. The initial conditions were drafted in a way to direct the thread to a particular solution, but then, all men have egos (yes, including me twisted: ) which led this thread to this length.

    we can go on for months arguing about this topic, but I guess we can conclude this thread in a healthy manner as well, by putting down the trade offs of each method. And I guess the moderator can do it best, after we have a reply from the OP.

    .... I didnt do it ! ....

  9. #19

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    Where as, a bulb will illuminate the whole room, so that you can see the object even if you are not pointing at it.

    But then, the sensors are not intelligent
    Right ... the sensors are not intelligent. But you are. The sensor will give you different values when it sees different parts of the line. It does not know what it is looking at. You have to make sense out of the sensor values and judge what the sensor is looking at. If you start from a point close to the edge of the line (and on the line) and keep going outwards, you will see a steady (analog) drop in the sensor values.

    About diffused light:
    Pardon me for getting in to discussing the light effects again but I thought these deserved a clarification.
    Diffused light is nothing but reflected light. Its the surface of reflection that matters. This 'diffused light' the thread has been talking about is the result of reflection from irregularities in the surface and hence is low in intensity. And as contrary to somebody's belief in the thread, no surface however smooth the maker claims it is can be smooth enough to not to cause these irregular reflections. You need angstrom-level accuracy to eliminate these irregularities.

    We can't argue out a possible design when it has been experimentally verified.

    It would be helpful if someone could post all possible designs discussed and then we can discuss the pros and cons of each. That would be a good way to end this thread.

  10. #20
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    Right ... the sensors are not intelligent. But you are. The sensor will give you different values when it sees different parts of the line. It does not know what it is looking at. You have to make sense out of the sensor values and judge what the sensor is looking at. If you start from a point close to the edge of the line (and on the line) and keep going outwards, you will see a steady (analog) drop in the sensor values.
    And for this, a directed light is far better, simple and more efficient!! And this was the point I always wanted to convey!!

    Nobody said the other design WONT work. I am saying because I have done it, have made more line followers than all the other robots that i have made - with LDRs, with IR, with illumination, without illumination, and blah - blah.

    The OP posted a question on a line follower with TWO sensors - ( and "filtering" the ambient light while using LDRs!!!! Now I want to know how people do it!) The problem statement was not genuine, the topic was not directed to a healthy discussion either. Line followers and the sensor placement possibilities can always be a good topic for discussion, but not when the constraints are kept like the one in this thread.
    .... I didnt do it ! ....

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