Position Encoding.

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Very well spoken indeed!

With slug man, it is always a battle of wits, which he seems to lose at, most of the time.

You should be ashamed of yourself coming out waving your arms fully loaded when confronting him. Just seems unfair picking on a defenseless socialist slugman.

Jamie

I wasn't looking for friends or buddies, as you say. And I wasn't looking for help either! I can fight my own battles, thank you.

And who is US? Are you speaking for a group or yourself?

I just thought you worded it well. If you want to make a mockery from a complement, So be it.

You must've had difficulties in your career maintaining a base line public relations strategy? Yes, I am very familiar with the type.

Must be an elderly thing. Something I'll see one day I hope, actually according to the stats, I'm not to far behind that mark.

Maybe this is more to your liking? Have a Rotten New Year.

Jamie

Holey crap, John, he doesn't even realize you are referring to you and him! No wonder he has comprehension problems.

He sure worded this last one well.

So, now you are a public relations expert? Got any diplomas?

Geeze, wot an opening!

Ouch! Did that hurt, John?

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The mental defect is the one that deludes you into thinking that you are being objective.

It may look like a phobia to you. On those occasions when I did consider the 555 it just couldn't do what I wanted - I can't recall any phobic reactions prompting me to curtail my consideration before I'd got through the relevant sections of the data sheet.

Absolute encoders are big and expensive. Tim Wescott's idea is only attractive if his encoder is less bulky and expensive than the - superior - absolute encoder. Your argument seems to be that because a big and expensive absolute decoder is practicable, roughly the same hardware can be used to build a cheaper and smaller absolute decoder. Can you see the problem here?

Note that in an absolute encoder, you can match the spacing of the various tracks to the spacing of multiple detectors, and the detectors stack up away from the axis of the shaft. In your version of Tim's encoder, the detectors are tangential to the axis of the shaft, and are looking at a small segment of the code wheel - n/(2^n-1). It would be a good deal messier.

Your point? Perhaps what you imagine to be your point. You've effectively proposed a less practical version of an absolute deocder, and want us to believe that it is going to be cheap and compact enough to compete with a regular absolute encoder, which does happen to strike me as a prime example of an approach that can be made to work but isn't usually the cheapest or most compact mechanism to keep track of the rotation of a shaft.

-- Bill Sloman, Nijmegen

-- Bill Sloman, Nijmegen

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The absolute encoder of shaft rotation is a good example of an approach that isn't the cheapest or usually the best approach to monitoring shaft rotation - they are too bulky and expensive for most applications, which is why the market is dominated by incremental encoders - so John Fields has just made an ass of himself.

Jamie is too dim to have noticed this.

A battle of wits? It was a massacre, and I'm still standing.

Jamie's imagination is leading him astray, not for the first time. If he actually understood what whas being talked about, he'd not have to rely on his imagination.

-- Bill Sloman, Nijmegen

Jamie's unreliable imagination misleading him again.

-- Bill Sloman, Nijmegen

There are many clever circuits using them floating around. I'm not saying that the 555 is an answer to all things, but you seem to be saying that "If I can't use it in my application, it can't be done".

So, what was it that the 555 couldn't do for you? Let's see if the group population can prove you wrong.

Cheers, John S

Until some one steps up to the plate and tells me something positive in your behalf, I'll have to put the pieces together the way I see them.

There must be some recent vacancies at the group home? You've seem to expend more network time than usual, lately. Are you guys sharing a recent departure's computer time?

Jamie

This one uses two detectors which are slightly less than one slot pitch (*x) apart.

It isn't the logic end, but it might make one think. The pots likely set the trigger edge on the detectors.

--- Since, in his original post, Tim stated: "I want to be able to use an encoder to rapidly -- but not immediately -- figure out the absolute position of a wheel.", it becomes evident that your braying at absolute encoders is irrelevant and your Ad Hominem attack unfounded.

Moreover, since I joined the discussion and endeavored to supply a little relevant help, all you've done is to supply rancor and sow the seeds of discord, so why are you really here???

Certainly not to help...

-- JF

To absorb the mass knowledge base from all the immortals here, in hopes that he'll be worth something in the public eye one day.

P.S. I wasn't pointing out who those immortals may be, you can wipe that smirk off your face!

Jamie

wow, all this talk about ancient technology..

Years ago I etched a PCB with 8 tracks on it using gray code. Eight hard copper fingers were connected to a 8 line to serial converter, which an old IBM XT desktop would be able to read the absolute position of a piece of equipment.

Later on, I updated that to an optical disc. I had photo developed at a local camera shop for 16 bit resolution where I sent groups of 2 of 8 bytes to the PC.

Worked flawlessly. Of course, the machine didn't need to move that fast. Just precisely back and forth. the machine had 3 axes and the PC had 4 serial cards which I had to get intermit with to poll the status register to determine which card was firing the shared IRQ and do a little change in the pull up output.

Of course, these encoders wouldn't send any information until you pulled down a control line from the serial port, so I also had a little more advance information there too.

Jamie

This was a tractor motor for a line printer head gantry. The old, high impact, fast running line printers that had acoustic enclosures around them because they were so noisy. So, it had fairly precise resolution on both rotational direction, and index.

The precision might have been fine, but the accuracy wouldn't have been so marvellous unless you paid attention to the centration. Centration generally limits encoder accuracy if only a single sensor is used. Two sensors at 90 degrees, or, better, three at 120 degrees, allow on-the-fly correction of decentration error.

Cheers

Phil Hobbs