I'm working on a line-following robot with my son. We've found a sensor array on Robot Shop that will help us but .. there's two and I'm not sure which will be the best for us.

The difference between them, as described in this PDF is "The QTR-8A uses a voltage divider for each sensor’s output while the QTR-8RC uses an RC circuit."

What I want to do is detect which sensor the followed line is triggering. All I need is a yes/no. But I'm too new to this to decide which of these two sensors would be best for me.

1 Answer 1


The main difference between the two models, as stated in the PDF you provided, is the output they provide to the MCU.

The QTR-8A will provide an Analog output, requiring a corresponding analog pin on the microcontroller. The QTR-8RC will provide a Digital output, but will allow the same accuracy of the QTA-8A by measuring the discharge time of the capacitor (HIGH to LOW time), with the advantage of higher accuracy due to the use of RC circuit instead of a voltage divider.

Both seems pretty straight forward, but for your needs, the QTR-8RC might seem more compatible, considering the Arduino Uno has 6 analog I/O pins (you didn't mention which Arduino is going to be used, the Arduino Nano has 8 and the Arduino Mega has 16), and that the QTR sensor provides 8 outputs. The way you could accomplish that with QTR-8RC and 8 digital I/O pins is described in the PDF:

  1. Turn on IR LEDs (optional)
  2. Set the I/O line to an output and drive it high
  3. Allow at least 10 us for the 10 nF capacitor to charge
  4. Make the I/O line an input (high impedance)
  5. Measure the time for the capacitor to discharge by waiting for the I/O line to go low
  6. Turn off IR LEDs (optional)
  • Great, easy to understand answer. Thanks @Omer! Dec 7, 2014 at 0:24

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