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  • digital inputs and switches

    Rule RE11 states "c. Passive electronics may be used as recommended by sensor manufacturers at the interfaces to the sensors". My interpretation of this is that you will not be able to add an external pull up resistor to a switch.

    It appears to me that you will not be able to wire 3rd party switches to the digital input port on the Modern Robotics Interface Module this year since you need the external pull up for it to work.. Modern Robotics is selling their version of micro switches now so there is a vendor supplied solution.

    Rev Robotics said their Expansion Hub has 10k pull up resistors on their digital input ports so you can use 3rd party switches with a Rev system.

  • #2
    The Modern Robotics Core Device Interface Module does support 3rd party switches on both digital and analog input ports and no external pull up resisters are required as there are internal resistors. A switch can be wired between 5v and signal.

    If you have any questions please contact support@modernroboticsinc.com or call MRI support at (786) 393-6886 (select option 2).

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    • #3
      Originally posted by Modern Robotics Support View Post
      The Modern Robotics Core Device Interface Module does support 3rd party switches on both digital and analog input ports and no external pull up resisters are required as there are internal resistors. A switch can be wired between 5v and signal.

      If you have any questions please contact support@modernroboticsinc.com or call MRI support at (786) 393-6886 (select option 2).
      If there are built-in pull up resistors, did you mean connecting a switch between signal and ground? Not 5V and signal.

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      • #4
        I am also interested in the answers. We are still not registered, so can't ask on official game rules forum yet.
        We were planning to use one of these and just replace switch with toggle switch

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        • #5
          ... one of these
          https://ae01.alicdn.com/kf/HTB1QS_1K...mit-Switch.jpg

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          • #6
            Note: If there is an internal pullup resistor, the Switch should be wired between 0 (zero) V (not 5V) and input.

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            • #7
              The two types of switches typically used in these applications are Single Pole Double Throw (SPDT), and Single Pole Single Throw (SPST). The best one to use is the SPDT like the limit switches available from MRI (http://modernroboticsinc.com/limit-switch-kit) as mentioned by 3805Mentor above but any SPDT switch could be used. This connects to all three pins and requires no additional external components. In this configuration, the signal is tied to ground by the switch when the button is not pressed and tied to 5v when the button is. This setup does not require a pull up/down resistor or an inline series resistor as there is already within the module.
              Common ---> YELLOW
              Normally Open NO ---> RED
              Normally Closed NC ---> BLACK


              If a SPST switch is used a 10K pull down resistor is required by design so that the input pin is tied to 5v when the switch is closed and pulled to ground by the 10k when the switch is open.
              Switch Input ---> RED
              Switch Output ---> YELLOW
              10k pulldown ---> Connecting YELLOW to BLACK

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              • #8
                After reading the replies, I realized the quick test I had done on the digital port of the Modern Robotics Interface Module was done incorrectly, so I started again.

                Using the sample program with no connection on the digital input it reports high. I attached a couple of test leads to the ground and signal. When my hands touched the insulating cover of each of the alligator clips the input went low. Ohm meter touching insulating cover reads infinite. Attaching a Fluke meter between ground and signal makes the input go low and the volt meter reads 3 mV. Using 20 Mohms just as an alternate test not surprisingly also causes the input to go low.

                I grabbed another Interface Module and got the same results.

                The REV digital input stays high and reads 3.3 volts ( 3 mV below power) with the DVM connected between signal and ground on the digital input. (Somewhere between 10k and 4.7k is the transition to false.)


                The internal pullup resistor appears to be an interestingly large value on the MR Interface Module. I don't think it would take much to get false lows.

                Comment


                • #9
                  Originally posted by Modern Robotics Support View Post
                  The two types of switches typically used in these applications are Single Pole Double Throw (SPDT), and Single Pole Single Throw (SPST). The best one to use is the SPDT like the limit switches available from MRI (http://modernroboticsinc.com/limit-switch-kit) as mentioned by 3805Mentor above but any SPDT switch could be used. This connects to all three pins and requires no additional external components. In this configuration, the signal is tied to ground by the switch when the button is not pressed and tied to 5v when the button is. This setup does not require a pull up/down resistor or an inline series resistor as there is already within the module.
                  Common ---> YELLOW
                  Normally Open NO ---> RED
                  Normally Closed NC ---> BLACK


                  If a SPST switch is used a 10K pull down resistor is required by design so that the input pin is tied to 5v when the switch is closed and pulled to ground by the 10k when the switch is open.
                  Switch Input ---> RED
                  Switch Output ---> YELLOW
                  10k pulldown ---> Connecting YELLOW to BLACK
                  You said the digital input ports have built-in pulllup resistors. If so, what is the "internal pullup resistor" value? With the SPST switch in "open" state, the voltage of the digital input pin will be a divider of Vcc. So for example, if the built-in pullup is also 10K, then the digital input pin will have a voltage of 0.5Vcc which is 2.5V. That's not "0" at all. It most likely reads "1".

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                  • #10
                    Mikets, I finally read their post carefully, it just says there is an internal resistance, I think they're talking about the resistance to the input, not a pullup..

                    I didn't see MR's post before posting. Yes, SPDT works, I wasn't thinking about that at all. My post would only apply to SPST.

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                    • #11
                      Originally posted by 3805Mentor View Post
                      Mikets, I finally read their post carefully, it just says there is an internal resistance, I think they're talking about the resistance to the input, not a pullup..

                      I didn't see MR's post before posting. Yes, SPDT works, I wasn't thinking about that at all. My post would only apply to SPST.
                      Hmm, I read it quite differently.
                      no external pull up resisters are required as there are internal resistors
                      In their suggested implementation, although there is no "pullup resistor", there is a pulldown resistor required for SPST. On the SPDT implementation, I would argue it is not a good practice to directly connect a signal pin to Vcc without a resistor. If you are going to have a resistor, I still think it's better to use a pullup resistor on the input pin than a pulldown.

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                      • #12
                        Yesterday I connected a 3rd party SPDT switch to a Modern Robotics Digital Channel, and can successfully read the digital input value.
                        Here are some references "from the source", i.e., Modern Robotics:
                        From http://modernroboticsinc.com/core-device-interface-module-2:

                        Digital Connector

                        Pin 1

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                        • #13

                          I seemed to have accidentally posted prematurely. Continuing my previous post.
                          Here are the specs from http://modernroboticsinc.com/core-de...rface-module-2[INDENT] Digital Connector
                          Pin 1

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                          • #14
                            I seemed to have accidentally posted prematurely. Continuing my previous post.
                            Here are the specs from http://modernroboticsinc.com/core-de...rface-module-2
                            Digital Connector
                            Pin 1

                            Comment


                            • #15
                              OK, this is not a great start to my posting as a new forum member. For some reason unknown to me, when I hit "PostReply", only the first 3 to 4 lines are getting posted, despite the Preview showing everything. Regarding what I was attempting to say - I was able to connect a 3rd party SPDT without external pull up resistors, and the state was correctly reflected in software using the DigitalChannel object. I have more to say, but am worried that I will generate yet another truncated post.

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