[Emc-users] Differental Input to PWM
Hi all, Note: Reposted with smaller attachment. I am trying to read an RS422 differential input and convert it to an analog based on the duty cycle, using a Mesa m5i20 Anything I/O board. Provided this post is under the maximum size allowed, the schematic is attached. I really only have access to the section labeled CABLE TO RF AMP INTERFACE CONNECTOR, so I can't at this point directly access the Pulse Generator. I wrote a simple component to convert PWM duty cycle to an analog (pwmtoa) which can be represented as follows: Bias Gain | | |__|___ | | Enable | | | | Out In | | |_| Where Enable and In are bits, and Bias, Gain and Out are floats. Under the current implementation, it just maintains a running average of the last 100 samples and outputs the average on time (0.0 to 1.0). When using a signal generator this component seems to be working quite well, at least for my purposes (error +/- 1% and latency of a couple msecs, which is more than adequate for my purposes). I set the base period and servo period out of phase with the signal (2kz) to make sure it does not keep sampling at the same point in the wave form. What I don't understand is how to covert this differential signal to single ended. I can see the differential signal on a scope (real one, not halscope), but when I try to reference the signal, or the not signal to ground I get nothing, either on the scope or as an input to the m5i20. Can anyone enlighten me on how to read this type of signal. Thanks, Eric attachment: RS422.jpg- Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://ad.doubleclick.net/clk;164216239;13503038;w?http://sf.net/marketplace___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Differental Input to PWM
You have to reference the signal with it's counterpart. The signal should have two pins, a plus and minus. A comparator would work to convert the signal to a single ended (referenced to ground) signal. or use a RS-422 transeiver chip (ST490AB). Jim C Eric H. Johnson [EMAIL PROTECTED] ics.com To Sent by: 'Enhanced Machine Controller emc-users-bounces (EMC)' @lists.sourceforg emc-users@lists.sourceforge.net e.net cc Subject 03/31/2008 03:04 [Emc-users] Differental Input to AMPWM Please respond to Enhanced Machine Controller (EMC) [EMAIL PROTECTED] sourceforge.net Hi all, Note: Reposted with smaller attachment. I am trying to read an RS422 differential input and convert it to an analog based on the duty cycle, using a Mesa m5i20 Anything I/O board. Provided this post is under the maximum size allowed, the schematic is attached. I really only have access to the section labeled CABLE TO RF AMP INTERFACE CONNECTOR, so I can't at this point directly access the Pulse Generator. I wrote a simple component to convert PWM duty cycle to an analog (pwmtoa) which can be represented as follows: Bias Gain | | |__|___ | | Enable | | | | Out In | | |_| Where Enable and In are bits, and Bias, Gain and Out are floats. Under the current implementation, it just maintains a running average of the last 100 samples and outputs the average on time (0.0 to 1.0). When using a signal generator this component seems to be working quite well, at least for my purposes (error +/- 1% and latency of a couple msecs, which is more than adequate for my purposes). I set the base period and servo period out of phase with the signal (2kz) to make sure it does not keep sampling at the same point in the wave form. What I don't understand is how to covert this differential signal to single ended. I can see the differential signal on a scope (real one, not halscope), but when I try to reference the signal, or the not signal to ground I get nothing, either on the scope or as an input to the m5i20. Can anyone enlighten me on how to read this type of signal. Thanks, Eric (See attached file: RS422.jpg) - Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://ad.doubleclick.net/clk;164216239;13503038;w?http://sf.net/marketplace ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users attachment: RS422.jpg- Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://ad.doubleclick.net/clk;164216239;13503038;w?http://sf.net/marketplace___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Differental Input to PWM
On Mon, 2008-03-31 at 08:09 -0400, [EMAIL PROTECTED] wrote: You have to reference the signal with it's counterpart. The signal should have two pins, a plus and minus. A comparator would work to convert the signal to a single ended (referenced to ground) signal. or use a RS-422 transeiver chip (ST490AB). Jim C Something like this? http://www.wallacecompany.com/machine_shop/RS422-1a.jpg -- Kirk Wallace (California, USA http://www.wallacecompany.com/machine_shop/ Hardinge HNC lathe, Bridgeport mill conversion, doing XY now, Zubal lathe conversion pending Craftsman AA 109 restoration) - Check out the new SourceForge.net Marketplace. It's the best place to buy or sell services for just about anything Open Source. http://ad.doubleclick.net/clk;164216239;13503038;w?http://sf.net/marketplace ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
