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Sensors - Answer Thread

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  • Sensors - Answer Thread

    Answers to questions posted pertaining to Sensors.

  • #2
    Intelligent Sensors

    Originally posted by FTC5975
    Is the pixy still a permitted sensor like last year?
    Assuming the Following:
    a) it is the sole device on a Device Interface Module (DIM);
    b) it draws less than the 150ma DIM maximum current;
    c) it is in this context only an I2C device
    Would the Pixy still be a permitted sensor?
    See also

    Answer: As long as an intelligent sensor (one that includes an embedded processor) does not provide a programming capacity to the user, it is legal. The Pixy referenced does not provide a programming API for the end user and is an example of a legal intelligent sensor.


    • #3
      USB Sensors

      Originally posted by FTC3491
      Hello from team 3491 FIXIT,
      We are wondering if it would be legal to use sensors that plug directly into the phone through a USB port on the power module. We have tested this and it is fully functional with the FTC_app. There is no asynchronous serial communication on the sensor module so using USB would allows teams to use a multitude of useful sensors. We are especially interested in using a USB webcam and or an HID Mouse.

      Thanks team 3941

      Answer: No. <RE11> only allows sensors that connect to and are powered by the Core Device Interface Module. <RE17> disallows all electronics not explicitly allowed via other rules.
      Last edited by Buckaroo Banzai; 10-10-2016, 12:34 PM. Reason: update title


      • #4
        Simple Interface Circuit Board

        Originally posted by FTC10723
        Would it be legal to have a custom printed / routed circuit board that consists entirely of copper traces, connector pins, and a legal I2C multiplexer? Reading the manual, this seems to be a bit of a grey area between RE14-J and RE17.

        RE11-E allows simple I2C multiplexers, so that is not in question

        RE14-J allows that "sensor wires and their connectors may be extended, modified, custom made"

        RE17 disallows "custom circuits"

        The circuit board would simply provide a more convenient arrangement of plugs to interface with the multiplexer.

        Answer: a simple circuit board that serves only to interconnect other legal electronics is allowed per <RE14>.j.

        Care should be taken to ensure that the circuit board is adequately insulated. In this particular case, the only power for the I2C multiplexer MUST come from the I2C connections available on the Core Device Interface Module.

        It would be prudent to bring a circuit schematic for the interface to all competitions and be prepared to explain the interface to the inspectors.


        • #5
          Passive Electronics with Sensors

          Originally posted by FTC9890
          Is it permissible to connect a passive resistor to a sensor (e.g. a switch) to allow it to be connected to the Device Interface Module? We'd like to use generic limit switches wired as in

          Answer: Yes. <RE11>.b explicitly allows the use of passive electronics at the interface to sensors.


          • #6
            Use of LED paired with sensor

            Originally posted by FTC9881
            Is positioning a white LED next to a light sensor (such as to improve line following sensitivity allowed per RE12?

            Answer: <RE12> does not limit the usage of LEDs. It provides guidance and limitations on how LEDs within a legal robot may be powered. As long as your proposed usage powers the LED in accordance with <RE12> it would be allowed.


            • #7
              Modifying PCB Circuitry

              Originally posted by FTC11190
              We have a purchased sensor that is a collection of discreet sensors combined with an I2C digital I/O interface on a single PCB.

              There is already a feature on the PCB that allows disabling the sensor array via I2C, but we would like to reverse this feature so it powers up disabled and we turn on via I2C. Conveniently this can be done by simply adding a SMT resistor to pullup an unbiased mosfet ... also conveniently there is a 5V input filter cap exactly 0603 away from the gate.

              We wanted to verify that adding a resistor to improve sensor usability is allowed as long as we can justify by schematic that it doesn't violate any safety function of the design.

              Answer: No. The modification describe is not allowed based on <RE15>. The modification is a change to the internal circuitry of the PCB. <RE11>.b allows for passive electronics to be added to sensors, but only at the interfaces to the sensors.


              • #8
                Sensor PCB

                Originally posted by FTC11190
                Thank you for the clarification about adding a resistor to a purchased PCB sensor array. Glad we asked.

                Just to be 100% clear we are allowed to design a pcb that combines an array of individual sensors, passive components and connectors and use i2c voltage sensor to read the sensors. We understand it can only be powered from device interface module, we need a schematic to explain its composition to inspectors and it cannot have any component that is programmable ... also it should be well insulated

                Answer: Yes. Also, make sure to pay attention to current capacity for any signals routed through the circuit board. The circuit board traces should be designed to ensure sufficient current capacity.


                • #9
                  Custom Sensor PCB

                  Originally posted by FTC6081
                  Is it legal for a team to use a sensor if it is a manufactured sensor mounted on a custom printed circuit board containing only passive components as recommended by the sensor manufacturer?

                  Answer: Yes. Be prepared to show a schematic of the circuit to the inspectors and discuss/describe the design as part of the robot inspection process.


                  • #10
                    Sensor w/ Embedded Laser

                    Originally posted by FTC4137
                    Is Adafruit's time-of-flight distance sensor:
                    The rules say that "compatible sensors from any manufacturer are allowed"; on the other hand, it contains "a very tiny invisible laser source".

                    Answer: No. Lasers of any form are not allowed per <RE12>


                    • #11
                      Custom Sensor Design

                      Originally posted by FTC7090
                      We are hoping to design and use an array of discreet, passive components as a rudimentary sensor. We would be using an array of resistors and switches to pass a voltage value into the CDIM. Would this be allowed under the rules? Thank you!
                      Answer: It appears that you are describing building a voltage divider network controlled by a set of switches. As described, the design is a custom circuit and does not meet the use of passive components as allowed in <RE11>.b


                      • #12
                        LED in Adafruit Color Sensor

                        Originally posted by FTC6282
                        Is it legal to use the LED included on the Adafruit TCS34725 ( color sensor? If not, will be sufficient to just ground the LED pin with a soldered wire rather than take up a slot on the CDIM? (The schematic: Thank you!

                        Answer: If the LED is being used as intended (i.e. as a light sources for reflected light sensing) it may be used. Grounding of the LED control pin is also acceptable


                        • #13
                          3rd Party Quadrature Encoders

                          Originally posted by FTC11115
                          The rules clearly specify which motors to use, but they don't mention anything about encoders.

                          My team is using the encoder ports of the motor controller to do telemetry on passive wheels and arm joints. We were unable to find I2C encoders and the Tetrix optical encoder isn't a good choice in their application.
                          Is it possible to use any 3rd part quadrature or 2-sensor encoders such as:


                          We would need to make a connector to only get the 5V, GND and channels A + B to the motor controller, but it should be compatible.

                          Team #11115 - Gluten Free

                          Answer: The sensors themselves are allowed. Connecting them to the motor controllers is not allowed. Current rules only allow 3rd party sensors to be connected to the CDIM (<RE11>).


                          • #14
                            Double Throw Switch

                            Originally posted by FTC11260
                            Our team would like to use a switch wired to a digital input port of the DIM. We want to use it to switch between red and blue versions of autonomous code. I told them we could use a touch sensor since it is a switch, but they would like to use the switch. It would be wired with a 10-50K resistor inline with the 5 volt wire to reduce current flow. Is this legal? Thanks for your reply.

                            Team # 11260

                            Yes, as long as the switch is wired as a sensor to a CDIM as allowed in <RE11>.a


                            • #15

                              Originally posted by FTC11100
                              "The team would like to use either a touch sensor (switch/digital sensor) or a potentiometer (analog sensor) to set parameters for the robot. That is, we would like to use a potentiometer to set a time delay for autonomous in situations where our alliance partner's robot may cross our robot's path. Rather than create multiple programs that delay 5-seconds, 10-seconds, ... for both red and blue. We would like to have a potentiometer that we can adjust (0 to 15 seconds) before each match to set the time delay. Is this legal?"

                              Answer: Yes, as long as the potentiometer is wired to a CDIM as allowed in <RE11>