Pulse Width Measurement in C

5 years 6 months ago #29530012 by beerbot
Having set an input to pulse mode (with the PC Utility or ^PMOD ?), I want to
then read the pulse width in my C program. RioReadPulseAnaInputs() is a "short."
How do I use that short as a pulse width measurement? Is it simply the width in microseconds?


Given that there is a millisecond or two delay in updating a pin's value, will the
pulse value be the width of the last pulse before the update, the average since the last update, or ...?

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5 years 6 months ago #29530013 by TechSupport
What exactly is this "short" it is reading? Is it a 0uS reading or something else I am not aware of?

To read back the pulse input, you can send a query of ?pi.

?pi 1 should query back the Pulse input 1 value.

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5 years 6 months ago #29530016 by beerbot
"short" is the C language data type that you define in the Datasheet C Library Functions for this read.

That is, you define the function RioReadPulseAnaInput() as a data type "short" (page 14, first function).

Since you don't use the modifier "unsigned," this means that the value returned by that function is a signed integer, likely 16 bits in size.

The question is, when the pin is set to "Pulse Input Mode" (^PMOD), what does the returned value represent?

For example, it could be the pulse width in microseconds or in Hz. Your "Power Stage Electrical Specifications" on page 9 of the Datasheet shows both duration and frequency values for pulse parameters.


I assume that when the pin is set to analog input mode the value represents the voltage in millivolts?

I want to use the C Library, not the console/basic commands, but the same question applies for ?pi 1. That is, what data is returned?

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5 years 6 months ago - 5 years 6 months ago #29530017 by TechSupport
Thanks for clarifying. I don't have any knowledge of the C language programming.

^pmod means that you are changing the pulse mode parameter for an input. If you are broadcasting to all inputs on the pulse, then 0 is used.

To change a pulse/analog input 1 from analog raw to pulse raw, then it can be done via a serial command which is ^pmod 1 2.

If you were to query the actual state of pmod 1, you would send ~pmod 1.

I've attached a screenshot using Robonav.

I queries the pmod to see what the states were.

Then I changed input 1 to become pulse raw.

Then I queried again to see that the change took effect, where position 1 went from 0 to a 2.
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