Just a couple additional notes, since I'm an electrical engineering student and happened to be wiring the sensor up today.
- The sensor acts like a switch that closes when it sees a white object. It's using transistors inside rather than a mechanical switch, but as far as the wiring is concerned it acts just like a limit switch (except that it needs +12V power). Like a limit switch, it has a "normally open" and "normally closed" output; one output will be high when it sees a light object, the other will be high when it sees a dark object. Look at the sensor datasheet for all the gory details.
- The digital sidecar has built-in pullup resistors, which means that unless you connect the GPIO pin to ground, it will have a value of 5V. This means you don't need any additional circuitry to hook up the photoswitches. See the Digital Sidecar datasheet for more information.
- The attached schematic tries to show the whole picture. Note that you could just as easily connect the black wire to the GPIO pin, it's just a matter of whether you get a "1" for dark or a "1" for light. (My apologies if I mixed up LO and DO on the schematic. Let me know and I'll fix it.)
- The part number is 42EF-D1MNAK-A(2). The 2 isn't given, but it's apparently part of the number based on Rockwell's part selection tool. If you haven't found it already, a CAD model (STEP) is available on Rockwell's site.
To those wondering how you program these things: it's a switch - a digital input - a 1 or a 0. Once you calibrate it, it will have one value when it's over the carpet and the other value when it's over the tape. All you have to do is read the sensor value to determine if you're on the tape or not.
If you have questions about how to follow a line, look at this
white paper from NI, or ask
an FLL student.