Line Detector Circuit Schematic

Discussion in 'The Projects Forum' started by Teg Veece, Dec 3, 2006.

  1. Teg Veece

    Thread Starter Member

    Mar 14, 2005
    I'm trying to develop a line detection sensor that basically sends back a TTL high signal when the sensor sees a line of a certain colour. I'll probably be using a white strip of insulation tape on a blue floor.

    Active Robots sell one of these sensors for $11 but I'd like to make one myself.

    I'm guessing that it require an IR LED and and tunable IR detector but I'm not too sure how to go about implement this detector. Could anyone provide a circuit diagram or point me in the right direction? Any help at all would be very much appreciated.
  2. beenthere

    Retired Moderator

    Apr 20, 2004

    Here's a site that details making such a robot line follower:

    Just as a note, IR detectors aren't tuneable. You might find filters to limit the IR frequency coming through, but the phototransistors or CDS cells normally used have a response that can't be altered. The possible problem with your tape is that you don't know the reflectivity in the IR region. It could be such that a line-following circuit will want to avoid your track-defining tape because it is invisible in the IR region. This is hard to tell in advance, as manufacturers don't tend to publish what their tape looks like in IR.

    There is an outfit called TAOS that makes a line of photosensors. They are a packaged light-sensitive diode and op amp combo in a TO-92 sized package. Response is from far IR to UV. With these, you might have a shot at a filter to tailor the response. Translucent colored film might do the trick. The TAOS sensors are available from for $1.37 a pop.
  3. n9352527

    AAC Fanatic!

    Oct 14, 2005
    From the picture, it looks like a standard comparator circuit where the output level from the IR sensor is compared to a preset value from the trimmer.
  4. Teg Veece

    Thread Starter Member

    Mar 14, 2005
    Thanks for the replies. I hope to replicate the active robots sensor as much as possible so I think I'll purchase an OPB745 alright.

    Is it just a case of supplying the IR diode of the OPB745 with a forward current then setting up a comparator circuit to go high when the PhotoDalington output voltage reaches a certain value (i.e. whatever value it goes to when the light is reflected off the white insulation tape)? Or is it more complicated than this. Also, is the PhotoDarlington's voltage or current proporational to the wavelength of light ir detects?