Support request for FPGA issues

[charles long]

Hi all:

I encountered a very strange problem with falling edge detection in my project.

#1
I used a "wait on falling edge" function in my program, In the field, while testing with live signals I saw there are noises (spikes) on the start signal line. And the program was triggered to start measurement many times even if no PCBA is moving. I suspect "wait on falling edge" function thinks noises/spikes are also falling edges.

#2
Therefore, I change the FPGA VI to use a event counting method shown in Page 5 of the white paper (attached). According to 7830R user manual, 0-0.8V is consider low & 2-5V is considered high. I can see from oscilloscope that all noises/ripples on the start signal line is in the range of 4-6V. So theoretically this type of noise should not affect high/low readings and therefore falling edge detection based on the event counting method. You can have a look at the small FPGA VI (without host program) test program I wrote (attached).

However, while running this FPGA VI itself. I can see the count number increasing even though there are no pulses and falling edges (only some small noises and ripples between 4-6V, as seen on the scope). And this is very strange. If I supply a very pure 5V DC without noises/ripples to DIO0, then the count number stays at 0 and doesn't increase.

See if you have any idea for such a problem.

Hope can receive your response asap!

Thanks

Charles long

[mrak1]

Hi,

I have seen similar issues when waiting for a prox signal or something similar on the FPGA ==> the input would trigger repeatedly during the rising edge and the falling edge of the pulse generated by a prox signal.

To get around this, I introduced some debouncing logic and that resolved my problem.  See the figure # 17 in this document:   http://zone.ni.com/devzone/cda/tut/p/id/2993  . This is similar to what I did but there are also a few other approaches.  If this doesn't work for you, let me know.

Good Luck!

Mike R.

[charles long]

Hi Mike R:

Thank your support, i have sovled this problem! thanks very much!!

charles long