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Line detection/electronics help

  1. Nov 4, 2006 #1
    I'm in an electronics class in which we build a sumo bot for our final project. Right now I'm working on the line detection using QRD1114 photo emitters/detectors. The problem is that the transistor is outputting about 2.4 volts (low) and 4.6 volts (high) on a 5 volt input, which is borderline for inputting into the LS family digital logic.

    I received a suggestion that I should use an LM741 op-amp with a low gain (~10) and tie 2.4 volts to the offset, so it nulls the low input and amplifies the high to the 5V rail. On the 741, there are two offset nulls, though I'm not exactly sure how to null out a 2.4 volt signal. Can anyone give any suggestions as to how to achieve this or possibly a better way to approach this problem? Thanks.
  2. jcsd
  3. Nov 4, 2006 #2


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    Staff: Mentor

    What supply rails do you have available? Probably the best way to process the output of the photo sensor would be to use a single-supply comparator, with its reference set between the high and low output voltages of the sensor. Be sure to include some hysteresis in the + feedback path of the comparator.
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