NPN interface and long distance handling

[sweethomela8]

I'm using devices which have a 250mA NPN output, I'm trying to use a FPGA to connect these NPN outputs to the FPGA inputs using a pullup resistor. These devices will be 50ft away from the FPGA or even more. Is there any design considerations I must take for this to be a good stable design? I've put in a strong pull-up resistor and a RC low pass filter. Is a buffer necessary even though the pull-up resistor is there? thanks.

 

[dick_freebird]

Low pass filtered inputs and high speed input buffers are prone to
chatter on ambient and self-switching noise. You'd want to use
a Schmitt type input, or segregate any chatter to the first few
stages (digital debounce) if you don't have options on the input
buffer personality.