Hi mt,
The method listed for removing glitches from the digital signal will
actually use another counter on your device. Thus you will be using two
counters; one to filter your signal by outputting pulses you specify
and another to read frequency in the same way that you are already
doing it. The only difference is that you are now reading frequency
from the signals being output by the first counter, which are set to
have a pulse width of the original signal plus the glitches. In this
way, the glitches are filtered out and the signal is debounced.
When using the DAQ Assistant for counter output, you can set the high
time and low time of the pulse in the Settings tab. Unfortunately, the
DAQ Assistant does not directly support retriggerable pulse generation.
However, there is a LabVIEW example using the DAQmx API that can be
found in the Example Finder (Help » Find Examples) under Hardware Input
and Output » DAQmx » Generating Digital Pulses » Gen Dig
Pulse-Retriggerable.vi. This example configures a task for CO Pulse
Ticks (relative to the timebase used as the counter source), but can
easily be changed to CO Pulse Time. You can then set the high time
(pulse width) and low time (delay) inputs to correspond to the pulse
you would need. The example then configures the start trigger to be the
gate of the counter where your signal to filter will be connected, and
sets this start trigger to be retriggerable using the DAQmx Property
Node. The counter will output a pulse whenever it receives a start
trigger, which, in this case, means whenever it sees a digital pulse on
the gate (corresponding to your signal). When configured correctly, you
should output a pulse each time the counter receives an input pulse,
only you can control the width (and therefore quality) of this output
pulse. Finally, you will need to create another counter task just as
before, and connect the output of the first counter to the second
counter to read the frequency. Hope this helps,
Daniel S.
National Instruments
