4 Replies Latest reply on Apr 7, 2009 6:06 AM by pmad

    Remote or external capsense

    don.merchant
              Hi,   
         
      I am wondering if I can use capsense if it is not located on the same pc board. For instance if I have a keypad that is external to the main pc board that contains the capsense ic, can I just run the capsense wires to my keypad buttons only? Will it work if the capsense chip is not directly mounted on the keypad?   
         
      Does anyone have any examples they can show or discuss?   
         
      Thanks in advance.   
        • 1. Re: Remote or external capsense
          jfmd

          Thanks for your inquiry.

          I just wanted to respond and let you know I'm working on getting the correct answer to your question and to see if we have some examples for you. Didn't want you to think I was ignoring you .

          Thanks!
          Jim

          • 2. Re: Remote or external capsense
            don.merchant
                    Any information yet?   
            • 3. Re: Remote or external capsense
              iain.galloway
                      You would need to shield the wires, as they would become capsense elements. There is a shield electrode, and it would have to surround the wires. Co-ax is the extreme, a wire wrapped around (might) work. Depends on the application, and how far away the sensors would be...BUT with the small size of the part, why not place it near the capsense pads, and communicate serially (uart or i2c) back to another "main" processor.   
              • 4. Re: Remote or external capsense
                pmad
                        Using wires running on a different board will increase the parasitic capacitance which in turn will reduce the sensitivity and will be more susceptible to noise. As suggested use shielded wires and try keeping the wires as short as possible and don't run any communication tracks closer to those wires. This can cause false detection. Also place a series resistor on the capsense lines of 560 ohm closer to the capsense IC.   
                   
                Regards   
                Pushek