bmann2000
2008-03-27 15:10:07 UTC
This may sound strange, digital filters are traditionally used to filter analog signals, but I need a filter for a digital signal.
I'm using a cRIO-9401 module to sample digital inputs, but due to system noise, sometimes I register a logic low when the input if actually at 5V, a look on the scope has revealed that occasional noise spikes below the TTL threshold are causing logic-0 levels to be briefly registered on the cRIO. The sampling rate of the digital input is 30Mhz, therefore, even though the noise spike only lasts for a tiny amount of time, the cRIO picks this up as logic-0.
I figure I need to implement a digital filter, preferably in a way that can be tuned to strike a balance between missing logic-0's and not recording noise spikes as logic-0. A real event would last for at least 10mS. Has anyone encountered this problem before, and has code? I can think of a few ways to implement the filter, but wondered if anyone had tried and tested code.
Thanks in advance for your suggestions.
I'm using a cRIO-9401 module to sample digital inputs, but due to system noise, sometimes I register a logic low when the input if actually at 5V, a look on the scope has revealed that occasional noise spikes below the TTL threshold are causing logic-0 levels to be briefly registered on the cRIO. The sampling rate of the digital input is 30Mhz, therefore, even though the noise spike only lasts for a tiny amount of time, the cRIO picks this up as logic-0.
I figure I need to implement a digital filter, preferably in a way that can be tuned to strike a balance between missing logic-0's and not recording noise spikes as logic-0. A real event would last for at least 10mS. Has anyone encountered this problem before, and has code? I can think of a few ways to implement the filter, but wondered if anyone had tried and tested code.
Thanks in advance for your suggestions.
