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Author Topic: differential mpg  (Read 1388 times)

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differential mpg
« on: August 23, 2015, 08:02:05 PM »
Maybe I overlooked something, but how do I set up an differential mpg? Under ports and pins I only see a setting for channel a and b, no a, a-, b, b-.  I tried only using the a and b, but I am getting random moves.  Not the same each detent click. I didn't see anything in the ess setting either. Am I missing something simple?
Don
Re: differential mpg
« Reply #1 on: August 25, 2015, 07:27:50 PM »
Hey Don,

There's no setup of a differential encoder - This is fully dependent on your hardware. If your pulse generator / smooth stepper / PoKeys / parallel port (hah!) doesn't have +A and -A (and +B and -B) inputs, there's no way to use your encoder...UNLESS!!! (unless) you use a differential line receiver chip, preferably dual - One channel for A, and one for B, or a quad if you have an index pulse you can't live without in which case you can use three of the four channels. Anyway, this $2 chip will convert the differential signal in to a single ended output that can go in to your little pulse generator of choice. This is OK, because you can use really short wires and the odds of the signal being corrupted are now small. That's the whole point of differential signaling - It's noise tolerant(ish)

On that note, single ended encoders are STUPID and have NO PLACE in a CNC machine. A car stereo? Fine. And sure, they use a few less wires and maybe cost a little less, but it's not enough to justify the risk of ruined parts or ruined digits and limbs.

Buy a $3 chip and make what you need, or spend $10 on one of these....

http://store.mesanet.com/index.php?route=product/product&product_id=287

Good luck and happy chips!
Re: differential mpg
« Reply #2 on: August 25, 2015, 08:29:34 PM »
That's is kind of what I thought. They list those as out of stock. Is this the same idea?
http://cnc4pc.com/product_info.php/c46-differential-single-ended-converter-p-401?osCsid=bijog421te3f5lh43k05pjubb4
Thanks
Don
Re: differential mpg
« Reply #3 on: August 26, 2015, 09:49:55 AM »
Hey Don,

That board from CNC4PC should probably do the trick. I used that same chip on a board I built years back for one of the CNC4PC MPGs that I needed a differential signal out of.

 I'd get rid of those modular jacks and solder the thing directly in place. RJ-45 gets used a LOT for encoders and it really shouldn't get used EVER. The twisted pair is great, but those jacks suck for machine tools, and the often solid CAT5 wire doesn't like constant flex.... Maybe not applicable in your setup. But I digress. Those boards should be great.

Good luck!
Re: differential mpg
« Reply #4 on: August 26, 2015, 07:19:52 PM »
Thanks I will get one from Arturo and see.
Don