Counter Input - Count Rising AND Falling Edges

[jrdwight]

Is there any way to count both the Rising AND Falling edges for a counter input? If I can't do it programmatically, I'm thinking I'd need to wire the signal into multiple channels, and count Rising on one and Falling on the other, then add the counts from each channel together.

[ZYOng · Accepted solution]

It depends if you use E series or M/X series. How to make E Series Counter to Detect Both the Rising and Falling Edges

[Kevin_Price · Accepted solution]

Building on ZYOng's answer...

Many modern era NI DAQ devices will support change detection with a digital task which you can configure to respond to both rising and falling edges.  Such changes cause a brief internal pulse of a signal known as the change detection event which you can then count with a counter.  Conceivably, you could also just keep track of the total # samples acquired from the DI task you configured for change detection.

M-series, X-series, and many cDAQ chassis are among the devices that will support this usage.

But also, FWIW, the total count for both edges will always just be 2x the count for 1 edge, plus or minus 1 count.  The only way to get a 2nd rising edge is if there was a falling edge in between the 2 rising edges.  They always come in alternating pairs, so their counts can never be more than 1 apart.

    My point is that in most circumstances, counting both edges *barely* tells you anything more than counting just 1 edge.  Consider that and evaluate whether you have a situation that benefits from the extra work of counting both.

-Kevin P

[jrdwight]

Thanks ZYOng and Kevin! I tried it both ways, and both were successful:

1. Use a separate counter for each edge parameter (rising or falling) and add the counts together

2. Configure a DI task to detect state change and use an event structure registered to the state change event to count the state changes

For context, I'm using this VI as a coarse measurement of a motor's position. The motor outputs 16 pulses/rev with 50% duty cycle. So in this case, detecting both rising AND falling edges was advantageous because it increases the resolution from 16 to 32 segments per rotation.