Ir photoreflectors for line following
Hai all...
I am building a line following robo now, and going to use Fairchild QRB1134 IR Photoreflectors.The data sheet is attached.
Some body pls tell me the connection diagram of the photoreflector with the micro and the logic behind line following.
Thanks in advance...
JABIR
connection diagram is shown in the datasheet. but how to follow a line you ask? well there are lot of ways. it all depends on how many sensors you got? if you have only one then you must ensure that the sensor sees black and if it looses it hi must make some turns to find it again.
if using 2 then the black line has to be between them at all times so when a sensors sees black robot must turn. same goes for 3 sensors.
connect the led to its power source through resistor!
then connect the photo transistor as you wold a resistor to ADC pin and read the voltage. also add a 100k resistor from that pin to GND (as i assume you connect the transistor between vcc and ADC.
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Hai ..
Thanks for help.
I have five sensors. so did u pls tell me the best configuration ?
and i am a newbie in electronics,ops: so u pls tell me a simple circuit without that ADC. If it is must, will u tell me the part number..?? :roll:
Pls explain with a schematic.
Regards
JABIR
well i suppose you are driving on a level ground. then put them all in a line perpendicular(on 90 degrees) with the black line. the distance between the sensors should be (robots width-3) / 5 (let say your bots width is 10 cm, then the distance is (10-3)/5=1,4cm).
then as i said before connect the internal LEDs to GND and vcc via 330ohm resistor. the receiver part should be connected like this:
C(white) to Vcc(+5v)
E(blue) to your micro-controllers input(analogue input is the best but i guess digital will do just fine also).
all E's are connected to DIFFERENT inputs.
and then hope it works
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Hi guys
Does any one know of a similar device that would detect a dot about 0.002 inch?
could you tell me how big it is in mm's. i cant picture a dot in inches. but if it's big enough most of the sensors can find it when positioned just right.
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a 2 mil (.002") dot is about .05 mm. some how, I don't think that's what you mean. with out magnification optics, I don't think it's going to be vary easy.
Is this still for line following? because that just doesn't make any sense to me.
there's no way you can find that dot with or without lenses or optics. only with a microscope i think. the beam of light is just too big (1mm) for that dot and the surface around the dot reflects more than the dot so the sensor doesn't see the dot.
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This sensor is designed to use for very short ranging distance. It is not useful for IR array for tracking the line. You can use the one as sensors of odometry to measure speed of wheels for PID control but do not use for other purpose of robots.
I recommend you to make your own IR array. To try search with keyword IR array for mobile robots.
Best
that's rather odd, I have 2 robots that use them to find a white line and avoid it. I guess all this time it's just been my imagination that they actually work. what's more odd is that they seem to be a standard sensor for line followers. Glad you straightened me out. I'll have to go tell the whole world to stop using them.
From the data-sheet:Originally Posted by philba
"The QRB1133/1134 consists of an infrared emitting diode and an NPN silicon phototransistor mounted side by side on a converging
optical axis in a black plastic housing. The phototransistor responds to radiation from the emitting diode only when a reflective
object passes within its field of view. The area of the optimum response approximates a circle .200” in diameter"
If it is a converging optical axis, then the field of view and hence the 'distance ' should be restricted. The reason it "works at any distance" may be due to the ambient light reflections rather than the internal LED light. This is not clear anywhere in the post. Nor is it clear if modulated light was used.
Usually, Line followers are just light reflection sensing setup. I sometimes wonder: why the expensive and hard-to-find reflective sensor?
A simple circuit using an LDR would, and are in many a place, work fine with a slit aperture!
The .200" diameter can be simulated/fabricated easily. The Mouse chopper wheel sensor module can be adopted for this by cutting and aligning the LED-photo transistor, similar to the QRDxxxx.
Please make clear something else
I gave you a general view point of how to build IR array for line follower in my knowledge but you can use the sensor to do so. I know somebody used the sensor for cheap line follower when they used only two sensor to detect left or right of line. Let see, if you do that so your robot would go in zic-zac line because you never know where is exactly central point between two sensors (normally 2 cm). So it is not precise feedback for PID control.
Try to design your own IR array with amplifier, cutter,... and using Lagrange intepolating polynominal to find the error of central point of IR array with line to adjust your PID to control you robots.
Good luck!
Uh, if you look at what i said, I never said I have 2 sensor line followers. The bots are minisumos and avoid the ring edge via those sensors. I don't disagree that 2 sensors isn't enough but that has nothing to do with the actual sensor type.
That sensor is used in quite a few robot designs to detect lines including many line following robots. I am directly disputing your comment that the QRB is not usefull for line following. The facts do not support your assertion.
People often put several of those sensors in a line (4-5) and create a very decent line sensing array. They are a bit large though. I have seen them used in numerous line-following competitions. I don't know if they are running off of ambient or not (I suspect not) but they work quite well.
frankly, a line follower doesn't need that sophisticated control.
Last edited by philba; 9th May 2006 at 05:18 PM.
with the QRBs, you mount them about 100-200 mils from the surface so the reflections work. I doubt they are being driven off of ambient light in that configuration. I used a digital camera display to watch them and there is ir illumination coming from them.
The aren't that expensive but i agree you can do cheaper. I built a 5 sensor array using surface mount IR Leds and phototransistors. I made my own PCB and light mask but total cost was less than a dollar. still, that is beyond most bot builders.
The reason why PTs are better than LDRs is that they are dead easy to interface to microcontrollers. No ADC, no comparators, just a pull-up resistor and a digital input pin per PT. for larger arrays, a shift reg can be used to reduce the pin requirements.
I might not indeed understand your purpuse at the first time. With Sumo competition, you can use only one sensor to detect black or while edge. You can borrow it from LEGO stuff which they have a lot available.
But you said that IR array for line-follower does not need sophisticated control is absolutely wrong. It is only simle for very simple scenario and low qualified competition where you do not need to adjust speed of robots, control robot to follow complicated line, opening and closing gate, passing turnel, going down stair... and something more. If you do that, you need very good imput of IR array so you need to apply your mathematical knowledge somewhere as I told about Lagrange Polynominal. You can go to robocup.dtu.dk to see how much is different from competitions you have seen.
Cheers,
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