Beacon SensorThe beacon sensor was a combination low pass and high pass filter that let both beacon signals into the Arduino. We used the interrupt pins and counted the number of rising edges per interval of time in order to determine frequency.
One bug we encountered was that the sensor would sometimes read a lower frequency than anticipated on the edges of the IR beam. So sometimes when looking for the 3k signal it would read 850Hz while turning. We somewhat this in the code by ignoring the first few reads of a 850Hz signal.
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Tape SensorThe tape sensor was a simple circuit attached to LM 393 Schmidtt trigger that read a logical high when it was over tape and a low when it was not. The tape sensor had a very small range of operation - it only worked well when placed 10-20mm above the ground. If it was too close it would always sense that it was off the tape and if it were too far it would always sense that it was on the tape (no IR being reflected back into the phototransistor)
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The tape sensors - one on the right and one on the left with outputs in the final row
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Other notes
We breadboarded all of our circuits in order to make them easy to modify and add to in case we messed up. Although we never needed to change the circuit components after they were added anyways