Hi everybody, I am building a line following robot but am facing a problem on the detectors since I don't know what type of infrared led and detector I must use. I searched on the net about the IR detector and LED but I found a lot of detectors some how acting as a transistor and some working as a diode…well that’s my schematic for the robot down if anyone have an experience on the line detector please assist me and thanks a lot
Ahmad,

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AY

 

Your post has been up for a day or so without any responses. I cannot comment on the circuit you present without building it myself. I would suggest you try the same and see what happens.

I can add some general advice:

1) IR detection based on simply having an IRED and detector is very susceptible to noise and false signals. I would suggest that you follow the common practice of using a modulated IRED and suitable demodulation for detection . For example, the IRED can be modulated at 38 KHz, which is then sub-modulated at around 1 KHz. Packaged units are available to do the decoding. Units by Sharp and Sony are readily available in the USA at surplus dealers. I have used the Vishay TSOP321XX with good success, and the new units are not much more expensive than the older, surplus units. The TSOP is about the size of a TO-92 transistor.
2) Perform a search on this forum using the term: line follower. There are numerous other threads on the same subject.
3) The following site has good suggestions and sample code for the 12F5XX or 12C series of PICs for IR detection and obstruction avoidance:

http://users.frii.com/dlc/robotics/projects/botproj.htm

4) Last, depending on how much work and innovation you want to do and how much time you have, I recommend you visit this site:

http://www.navfltsm.addr.com/ndb-nav-history.htm

The “four-course radio range” was used for aircraft navigation until the mid-1950's. One could make an analogy between that method and a line follower. For example, the left IRED could transmit one code, and the right IRED could transmit another code. When exactly on the line, the codes would mix, and hypothetically, an error signal proportional to the deviation from the line could be calculated. The biggest problem I can see at the outset would be to get a line that reflected IR a lot better than the background. Since I have never tried any such thing, I have no suggestions to give you, but it seems to me that any line follower based on IR will have to solve that same problem to some extent.

Good luck. John

 

use phototransistor, it does not require modulation

 

take a look at the qrb1134 http://www.junun.org/MarkIII/datasheets/QRB113x.pdf

it does a decent job, has a built in shield and a daylight filter. junun.org sells them for $1.50 but others carry them too. I have several bots that use them and they work fairly well.

yes, you can build your own for much cheaper but note that there are lots of issues about shielding since it has to work via reflections. the '1134 is pretty well designed so you might want to borrow from it's design.

on your circuit. I think you want more than 2 sensors. with just 2 your bot will wander back and forth - how will it know where it is over the line. I suggest at least 3 sensors and many good line followers use 4 or 5. code complexity runs from very simple up to very sophisticated. I'd start by doing a state diagram for the sensor values.

 

you can just use the photoreflectors

 

How would you use more than two? The only thing I can think of is running down the length of the bot, depending on steering method?

I've built a line follower before, and two worked fine...used the right-hand method because it was more like a maze. (we used a variant of the same code for our maze bot, which turned out to be fortunate...our line follower died on competition day so we hot-glued the sensors to our other bot and re-dumped the code...the judges thought it was innovative =D)

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-Ian

 

think about how you use 2. If the left sees a line, turn right and if the right sees a line, turn left. that leads to a zig-zag path and much slower running time. If you had 4 equally spaced across the front of the bot, you would turn less if you saw a line with the inner sensors and thus run a straighter and faster line.

 

Have a look at This line follower. It uses 5 sensors and has a very good explanation of how they work and a circuit diagram. There is also video of it running with just Proportional control and then with Proportional and Differential control. Very informative.

Mike.

 

Thanks for the replies...it seems so obvious now (like most things).

When I did mine I didn't have it hug the line. It assumed that the line was between the sensors and only adjusted itself if it hit a line (using differential drive).

I'll have to build a multiple-sensor bot this year!

Thanks!

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-Ian

 

Halla ahmad, kiffak! isa meni7, salamt le kel lebnam wal mokawma, Alby ma3akom

well i wrote an article about IR proximity sensors.. using nothing but IR leds.. no photo-transistors, ne photo-diodes.. it can belpful to beginers

http://www.ikalogic.com/prox_sensors.php

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Ibrahim Kamal
check my electronics and robotics page: http://www.ikalogic.com/