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  • Sensors - Answers

    Answers to questions about Sensors.

  • #2
    Originally posted by FTC3805
    Question: We have Sharp IR distance sensors.

    https://www.pololu.com/product/2464

    https://www.pololu.com/product/2450




    These require 5 volt power. Are we allowed to use the 5 volt power port to power these sensors?

    The spec sheet does not show the signal output exceeding 3.3 volts, so they do not need level shifting.

    Even if an analog signal did exceed 3.3 volts, RevRobotics has stated to me that exceeding 3.3 volts on the analog input pin will not damage the Expansion Hub, the signal will just be clipped to 3.3 volts.


    Answer: There is nothing in the rules that prohibits connecting sensors to the 5V power ports on the Rev Expansion Hub.
    Last edited by Harold Oxley; 09-22-2017, 04:56 PM.

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    • #3
      Originally posted by FTC3805
      Question: A simple passive voltage divider of 2 resistors is all that is required to make a level shifter for 5 volt output analog devices. My interpretation of the game manual seems to indicate that this would have to be a recommendation explicitly stated by the manufacturer to be legal.



      Answer: Unless explicitly suggested by the manufacturer, this voltage divider would be considered a custom circuit and not allowed per <RE17>
      Last edited by Harold Oxley; 09-22-2017, 04:56 PM.

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      • #4
        Originally posted by FTC7244

        Subject: 12V Sensors

        Q: In rule <RE11> it states Compatible sensors from any manufacturer may be connected to the Core Device Interface Module or REV Expansion Hub. Does this mean we can use a 12V sensor that is powered by the Rev Expansion Hub, and with the sensors outputs into the sensors ports of the hub?


        A: There is nothing in the rules that would prohibit the usage of a 12v sensor. However, there is a high likelihood that the sensor would not be compatible with the REV Expansion Hub as the allowed Logic Level Converter is explicitly 5v to 3.3v

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        • #5
          Originally posted by FTC11411

          Subject: Is the CMUcam5 Pixy sensor legal?

          The CMUcam5 Pixy (http://cmucam.org/projects/cmucam5) sensor was deemed legal last year. Is it still considered a legal sensor this year?

          From RE11:


          This would seem to be a compatible sensor as it connects through I2C (among other interfaces).


          A: Yes. The CMUcam5 Pixy is an allowed sensor. Be aware that you will need to use Logic Level Converters for the i2c connection.

          Comment


          • #6
            Originally posted by FTC11411

            Subject: NXT Light Sensor

            Q: Over the summer, the kids experimented with using an NXT light sensor connecting to the analog port of the Modern Robotics Core Device Module. They perused the Lego NXT documentation and used resistors to get an analog signal readable from Java. They were doing this with an eye towards using this with the REV Robotics Expansion Hub this year as well as creating a video and sharing their code and how they did it with the community. While they didn't complete testing with the REV Robotics Expansion Hub (the first one we ordered had a hardware fault and had to be returned for a replacement), they believe they would be able to connect it to an analog port of the expansion hub.

            In looking over the rules, it would seem that this is not allowed this year as there is the definition of legacy sensors:


            A: Your understanding is correct. The NXT light sensor is a part of the family of Legacy Sensors and must be connected to a Core Legacy Module per <RE11>.g. Additionally, the usage of the resistors at the interface would have to be recommended by the manufacturer to be an allowed usage of passive electronics per <RE11>.c

            Comment


            • #7
              Originally posted by FTC9761

              Subject: I2C to SPI Bridge

              Q: There is a type of sensor we want to use that is only available in SPI. No I2C version is available from any manufacturer. There is an I2C to SPI bridge / converter available that works basically like a level-shifter: you plug the I2C cable from the REV module in one side and the SPI cable from the sensor in the other side. It doesn't change the sensor data, only the communications protocol. Except for being SPI the sensor would otherwise be legal. Would using the I2C to SPI bridge be allowed?


              A: Under the current rules, an I2C to SPI bridge would be considered to fall into the general category of "Additional Electrons" as covered by <RE17> and would not be allowed.

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