On Tue, 12 Jan 2010, Flying Electron wrote:
> Date: Tue, 12 Jan 2010 15:47:34 -0800
> From: Flying Electron <[email protected]>
> Reply-To: "Enhanced Machine Controller (EMC)"
> <[email protected]>
> To: "Enhanced Machine Controller (EMC)" <[email protected]>
> Subject: Re: [Emc-users] PWM input to EMC2
>
> I've got a pressure sensor that I'd like to use as a probe. The sensor
> has a value from 0 - 1023 based on the amount of pressure applied. The
> sensor is read by a microcontroller and the microcontroller can generate
> a pwm signal based on the sensor value. I was thinking that EMC2 could
> read in the PWM signal and reconvert the PWM signal back to a number
> from 0 - 1023 which could then be fed into a comparator in HAL to
> generate the probe signal. I think doing it this way would allow me to
> vary the trip point by varying the comparator input.
>
> The only two ways I have figured out how to get an analog value into
> EMC2 through a parallel port is either PWM input or pulsing an input pin
> at a frequency and having an encoder trigger off the pulses and read the
> velocity from the encoder. Maybe I am making this too complicated and
> there is a simpler way?
>
> Thanks!
>
> Sebastian Kuzminsky wrote:
>> Flying Electron wrote:
>>
>>> I've been looking through all the realtime components and haven't seen
>>> anything obvious. Is there a component to read a PWM signal in from a
>>> parallel port pin?
>>>
>>
>> That's backwards from how we usually do it - pwm generally comes *from*
>> emc2, goes *out* the parallel port, and then goes in to a servo amp or
>> similar.
>>
>> What are you trying to do?
>>
>>
>>
Depending on the microcontroller, if you are only using one PWM channel, you
may be able to output a variable frequency by changing the PWM resolution.
Also, if the required bandwidth is low, you could have EMC randomly sample the
PWM input at the base thread rate and low-pass filter the result. In this case
you need to chose your PWM frequency so the beats are high enough frequency to
filter easily
Peter Wallace
Mesa Electronics
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