5 Replies Latest reply on Feb 28, 2017 5:06 AM by j-man

    Eliminating Signal Noise via PSoC HW

    j-man

      Hello everyone,

         

      First time posting so I'll do my best to explain this the best I can. We have an application that uses a Pull-Up Resistor pin-out to a control button that has a wire that can span 50+ feet. Since this wire can get quite long, it is prone to electrical noise in particularly noisy environments (much like a giant antenna). I have employed a "Glitch Filter" to put in a 150ms delay time any signal sent to the chip in order to remove 90% of the signal noise that we have been picking up in our application. However, since it is a Pull-Up Resistor, from I understand the largest level of hysteresis that I can achieve is 3.3v from what I've seen on the scope. I've managed to send noise into the chip upwards of 5-6V P-P at over 400khz without getting a response, which is fantastic.

         

      I've included a slapped together illustration of what the application looks like. Fairly straight forward. While I have managed to remove 90% of the noise, when you include VFD's (Variable Frequency Drives) into the equation, the noise can occasionally bypass the 150ms delay. VFD's are so unbelievably noisy that even they can occasionally break through the filter barrier.

         

      Now this is a question to you folks that know far more than I do, is there a way via software (supporting electrical hardware is locked in for this particular application) that I can keep no more than 150ms delay time on the signal but perhaps some other way to increase the hysteresis level or some way to eliminate the false grounding on the Pull-Up?

         

      Thank you.

        • 1. Re: Eliminating Signal Noise via PSoC HW
          user_342122993
                  Try the Debouncer component instead of Glitch filter. They serve same purpose, but in different way. Please, please add a capacitor on the noisy pin! Honestly, I am surprised that PSoC survives industrial environment without digital isolation.   
          • 2. Re: Eliminating Signal Noise via PSoC HW
            user_242978793

            Use a coax cable and ground the shield should remove the noise pickup. Or use a Psoc Ble device.

            • 3. Re: Eliminating Signal Noise via PSoC HW
              j-man

              Try the Debouncer component instead of Glitch filter. They serve same purpose, but in different way.
              Please, please add a capacitor on the noisy pin! Honestly, I am surprised that PSoC survives industrial environment without digital isolation.

                 

              This is a project that I inherited from a previous colleague, which is why the hardware cannot be modified (such as adding an analog filter or capacitors). The former setup was using a debouncer which is not properly equipped to handle severe noise, only mild noise such as from a push button switch.

                 

              Use a coax cable and ground the shield should remove the noise pickup. Or use a Psoc Ble device.

                 

              Unfortunately, that option would get prohibitively expensive. Again, the hardware cannot be changed, all that I have to work with is the PSoC 3 architecture.

              • 4. Re: Eliminating Signal Noise via PSoC HW
                user_1377889

                So my question is: Is the wire to the button not shielded? This is a design bug which is nearly not correctable. What kind is the switch? Human acted? then you can exceed the debounce period to 1/10s.

                   

                 

                   

                Bob

                • 5. Re: Eliminating Signal Noise via PSoC HW
                  j-man

                  Bob: Correct. It is human acted that can't exceed approximately 150ms since anything more than that, it would cause some inconvenience for end users in terms of button 'holding'.

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