Re: [Emc-users] Analog to PWM or pulse-train ?

[Peter C. W. <pc...@me...>]

On Sat, 19 Jan 2008, Javid Butler wrote:

> Date: Sat, 19 Jan 2008 14:29:37 -0600
> From: Javid Butler <jav...@co...>
> Reply-To: "Enhanced Machine Controller (EMC)"
>     <emc...@li...>
> To: "Enhanced Machine Controller (EMC)" <emc...@li...>
> Subject: Re: [Emc-users] Analog to PWM or pulse-train ?
> 
> There is a simple way to convert analog to PWM using a comparator, but it
> will probably be faster to simply do it in a PIC if you only need one of
> them. With the PIC you just set up a PWM output and an analog input and copy
> the latter into the former.
>
> To convert analog to PWM you take a triangle wave into one input of a
> comparator and the analog input into the other input. The triangle wave
> should be the same amplitude as the analog input. Which signal goes to which
> input will determine the polarity of the output. The thing that takes time
> in a one-off is generating a temperature stable triangle wave of the right
> amplitude.




You can also make a simple charge-balance PDM generator with a comparator 
(with a little hysteresis) followed by an integrator (maybe just an R/C 
filter) , the integrator output fed back into the '-' comparator input, the 
'+' comparator input being the analog input. If the comparator output was 
sampled at say 10 KHz for some period and the times is was sampled high 
counted, you would have a crude A-D...



>
> Javid
>
> ----- Original Message -----
> From: "Anders Wallin" <and...@he...>
> To: "Enhanced Machine Controller (EMC)" <emc...@li...>
> Sent: Saturday, January 19, 2008 1:22 PM
> Subject: [Emc-users] Analog to PWM or pulse-train ?
>
>
>> Hi All,
>>
>> My VFD has an analog output which can be programmed to indicate either
>> output frequency, current, or power etc.
>>
>> I'd like to read this into EMC so I can monitor and plot the spindle
>> load while the machine is running.
>>
>> I have a M5i20 card which doesn't have analog inputs, so I'm wondering
>> if any of you know a nice simple way of converting the 0-10 V into
>> either PWM or a pulse-train (FM) or something else that can be read by
>> one IO pin (read say every 0.1 ms) on the m5i20 ?
>>
>> I know a small 8-pin PIC could do this easily but if there are ICs that
>> do this out there I'd like to avoid the programming...
>>
>>
>> Anders
>>
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Peter Wallace
Mesa Electronics

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