measuring 0 to 360 degree

[karthik bala guru]

Hi,
I would like to have different levels of voltage for every 30 degrees
so that i would be able to manipulate it using my processor.
i would like to have one sensor for measuring of 0 to 360 degree
and generating the corresponding signal in a single pin to
the processor.
Do kindly give me some info.

Thanks & Regards,
karthik bala guru

 

[Winfield Hill]

karthik bala guru wrote...

I would like to have different levels of voltage for every 30 degrees
so that i would be able to manipulate it using my processor.
i would like to have one sensor for measuring of 0 to 360 degree
and generating the corresponding signal in a single pin to
the processor.
Do kindly give me some info.

There are many types of angular encoders available with a full
360-degree digital range. You may find it easier to work with a
"360" degree potentiometer, sometimes found on eBay at reasonable
prices, and digitize the pot's position with a single A/D pin on
your uP. However these pots don't function over a full true 360
degrees, because they have a small dead band. You can use two of
them offset by 90 degrees, etc., and digitize using two uP pins,
using their overlapping ranges to cover the 360 degrees.


--
Thanks,
- Win

 

[Ken Taylor]

"karthik bala guru" <bluekarthik@yahoo.com> wrote in message
news:af94616b.0411160109.413145c8@posting.google.com...

Hi,
I would like to have different levels of voltage for every 30 degrees
so that i would be able to manipulate it using my processor.
i would like to have one sensor for measuring of 0 to 360 degree
and generating the corresponding signal in a single pin to
the processor.
Do kindly give me some info.

Thanks & Regards,
karthik bala guru

Search out terms such as "servo potentiometer" and "synchro to digital
converter".

Ken

 

[Ban]

CFoley1064 wrote:

How about every 22.5 degrees (360 degrees/16)? There are a number of
inexpensive 4-bit mechanical encoders (such as Grayhill
26ASD22-01-1-AJS, available as Digi-Key P/N GH3076-ND for $13.87 USD)
which provide 4 mechanical SPST switches to a common and give a 4-bit
BCD output. You could easily use this with pullups, a CMOS inverter
IC, and a few resistors to create an analog output voltage.

VCCVCCVCCVCC
| | | |
.-..-..-..-.
22k x 4| || || || |
| || || || |
'-''-''-''-'
| | | |
8_/ | | | | |\ ___ Vo
.---o/ o---o--|--|--|---| >O-|___|-o--o
| | | | |/ 100K |
| | | | |
| 4_/ | | | |\ ___ |
o---o/ o------o--|--|---| >O-|___|-o
| | | |/ 200K |
| | | |
| 2_/ | | |\ ____ |
o---o/ o---------o--|---| >O-|___|-o
| | |/ 400K |
| | |
| 1_/ | |\ ___ |
o---o/ o------------o---| >O-|___|-'
| |/ 800K
===
GND
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

Hope this is of use. Questions such as this usually receive a better
response on sci.electronics.basics.

Well, hopefully the responses will be better, because this circuit will not
be linear at all. :-((
It can be achieved with summing the currents into the -input of an opamp and
inverting the sum.
--
ciao Ban
Bordighera, Italy

 

[Winfield Hill]

Kryten wrote...

If Winfield is the co-author of The Good Book (The A of E) then
I am sure he will have valuable comments on telescope shaft encoders.

Comments perhaps, but valuable? When answering the O.P., I couldn't
help think of our high-resolution encoder for the MMT telescope, for
which I made the control system in the early 70s, under contract to
the Smithsonian Astrophysical Observatory. How much resolution?
I don't remember exactly, but pick a big number, 24 bits, 32 bits,
48 bits, etc. Anyway, much too high for our O.P. friend to consider.


--
Thanks,
- Win

 

[CFoley1064]

Subject: Re: measuring 0 to 360 degree
From: "Ban" bansuri@web.de
Date: 11/16/2004 6:05 AM Central Standard Time
Message-id: <h2mmd.176206$b5.8817015@news3.tin.it

CFoley1064 wrote:

<blather before finishing first cup of coffee>

Well, hopefully the responses will be better, because this circuit will not
be linear at all. :-((
It can be achieved with summing the currents into the -input of an opamp and
inverting the sum.
--
ciao Ban
Bordighera, Italy

Sorry -- you're right, of course. Next time I'll make sure I'm awake before
posting. Thanks for the spot.

Chris

 

[Rich Grise]

On Tue, 16 Nov 2004 01:09:33 -0800, karthik bala guru wrote:

Hi,
I would like to have different levels of voltage for every 30 degrees
so that i would be able to manipulate it using my processor.
i would like to have one sensor for measuring of 0 to 360 degree
and generating the corresponding signal in a single pin to
the processor.
Do kindly give me some info.

How about a wheel mouse wheel? You have a computer there already
anyway, right? Tying it in along with your regular mouse, or
even using it in lieu of a mouse, isn't hard at all, electrically,
but of course, you'd have to write code to read the mouse registers.

Good Luck!
Rich

 

[Kryten]

"Roger Hamlett" <rogerspamignored@ttelmah.demon.co.uk> wrote in message
news:IHnmd.56$Zf4.37@newsfe6-win.ntli.net...

Seriously, you are not even going to approach the accuracy of a cheap
encoder this way, without becoming more expensive than the encoder. The
problem is that for repeatable operation, the light, sensors, and all the
amplification, must remain stable.

As for stability, the signals have to be viewed as their attenuation of the
reference beam. So even if the intensity of the LED varied, the attenuation
should remain the same.

a disk that would beat the
accuracy of the polarising sensor system, can be printed on a laser
printer...

Such a disk is always limited to a particular finite number of positions.
The analogue is limited by the ADC resolution.

Encoder disks, are not as expensive as you seem to think. For example, a
company near me, will make custom disks/cells up to 4" in diameter, with
repeatability better than 0.25 arc seconds, and resolution better than 0.5
arc seconds, for well under $200, in 'one off' quantities.
Most telescope systems use incremental encoders, which are a lot cheaper.

Well, $200 is expensive for me :-(

I suppose if I could afford a scope that required high accuracy, the
encoders would be a small fraction of that cost.

For all the telescopes I am ever likely to own, the laser printed encoder
will probably do.

 

[Rich Grise]

On Tue, 16 Nov 2004 22:44:34 +0000, Kryten wrote:

I'll get back in touch with my local astronomy club. They reside next to
the Greenwich observatory, which is now located in Cambridge.

They moved GREENWICH?????!?!??!

My god, what's that going to do to all of our clocks?

What's next? Stonehenge? The Great Pyramids? Abu Simbel? - oh, wait.
never mind on that last one...

;-)
Rich

 

[Winfield Hill]

Kryten wrote...

Winfield Hill wrote ...
Kryten wrote...

If Winfield is the co-author of The Good Book (The A of E) then
I am sure he will have valuable comments on telescope shaft encoders.

Comments perhaps, but valuable? When answering the O.P., I couldn't
help think of our high-resolution encoder for the MMT telescope, for
which I made the control system in the early 70s, under contract to
the Smithsonian Astrophysical Observatory. How much resolution?
I don't remember exactly, but pick a big number, 24 bits, 32 bits,
48 bits, etc. Anyway, much too high for our O.P. friend to consider.

Going O.T. a bit, just how does one begin to get that kind of angular
precision?

You pay the big bucks to a company that specializes in such things. :&gt


--
Thanks,
- Win

 

[Kryten]

"Rich Grise" <rich@example.net> wrote in message
newsan.2004.11.17.00.47.20.467256@example.net...

On Tue, 16 Nov 2004 22:44:34 +0000, Kryten wrote:

They moved GREENWICH?????!?!??!

My god, what's that going to do to all of our clocks?

What's next? Stonehenge? The Great Pyramids? Abu Simbel? - oh, wait.
never mind on that last one...

Just the observatory of course.

The actual Greenwich meridian was officially declared as the cross-hairs in
the eyepiece of the Transit Circle at the observatory in 1884, and is marked
at several places in Greenwich (incl. the old observatory). a line where
tourists can take a photo with a leg in each hemisphere.

However I heard that the UPS system (and some other sources) are off by the
order of tens of metres.

Perhaps someone with a good UPS gadget in London can check that out?

Plus there is the problem that things don't stay put.

Dang pesky tectonic plates doing their continental drift, stars doing
stellar drift, and even the first point of Aries is no longer in Aries
thanks to our wobbly planet.

 

[Tim Shoppa]

"Kryten" <kryten_droid_obfusticator@ntlworld.com> wrote in message news:<Nynmd.183$im.145@newsfe5-gui.ntli.net>...

I imagine they have quite sophisticated stuff inside, like a grey-coded disk
or inductive coils.

I'd like something cheaper, e.g. for amateur telescopes.

I wondered if it would be possible to shine (or reflect) a LED through a
disc of polarising material, then pass the light into a pair of photosensors
with similar polarised material with the polarisation angles at 90 degrees
to each other.

As the shaft rotated through 360 degrees, the light through each photosensor
would vary
(ideally in a rectified sinusoid form, but in practice it will differ).

The ratio of signals from the two sensors (w.r.t. the original beam)
would indicate the absolute angle 0 to 90 degrees.
You would need a way to tell which quadrant you were in of course.
Perhaps three sensors at 60 degrees to each other for a 3-phase system.

The advantage would be that it should be fairly cheap to make, because you
don't need a precision gray-coded disc or whatever. If the light beam is
shone over a large enough polariser area, then small defects have less
effect.

The disadvantages include having to compensate for whatever non-linear
response the sensors give, and imperfect 60 degree alignments, but I'm sure
this can be solved by a little ingenuity.

Maybe to the few degrees level. But a protractor and a pointer gets you
accuracy better than that and doesn't need any electronics at all,
right?

A very similar idea, using gratings and counting light/dark cycles,
will easily get you a precision of a few arc-minutes of
angle. The gratings needed are off-the-shelf items from Edmund
Scientific etc. The taut band needed to convert rotary position to
linear position could come from an old floppy drive. I suspect
that the coefficient of expansion of the materials used would be the
limiting factor in a typical telescope's environment. You still need
to properly "zero" your coordinate system of course.

Tim.

 

[Spehro Pefhany]

On 17 Nov 2004 15:19:38 GMT, the renowned Daniel Haude
<haude@kir.physnet.uni-hamburg.de> wrote:

On Tue, 16 Nov 2004 22:44:34 GMT,
Kryten <kryten_droid_obfusticator@ntlworld.com> wrote
in Msg. <mpvmd.318$im.193@newsfe5-gui.ntli.net

Comments perhaps, but valuable? When answering the O.P., I couldn't
help think of our high-resolution encoder for the MMT telescope, for
which I made the control system in the early 70s, under contract to
the Smithsonian Astrophysical Observatory. How much resolution?
I don't remember exactly, but pick a big number, 24 bits, 32 bits,
48 bits, etc. Anyway, much too high for our O.P. friend to consider.

Going O.T. a bit, just how does one begin to get that kind of angular
precision?

Hm, 1 micron resolution is standard for linear optical encoders used in
machines like mills and lathes. 48 bits is about 3e14, that would
correspond to 3e5 kilometers or the circumference of a circle of 50000
kilometers in diameter (more than three times the Earth's diameter). Buy
this length of enocder from Heidenhain (bumping the German GNP to
unknown heights), paste it round a circular wheel and presto -- 48 bit
angular resolution.

No frickin' way you had or needed that kind of precision, Win.

OTOH, 24 bit gives you about .08 arcsecond precision, correspondign to a
1um scale on a 3m wheel. Good enough for a telescope? I don't know.

--Daniel

Page 20 of this catalog has some Heidenhain encoders they say are
suitable for telescopes (up to 27 bits).

http://filebase.heidenhain.de/doku/brochures/pdf/350_457-25.pdf



Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

 

[Kryten]

"Daniel Haude" <haude@kir.physnet.uni-hamburg.de> wrote in message
news:slrncpmr0b.10t.haude@kir.physnet.uni-hamburg.de...

No frickin' way you had or needed that kind of precision, Win.

Yes, we can do the maths too.

It was just an off the cuff comment, indicating a shedload of bits.

 

[Kryten]

I'm sure you can buy shaft encoders but they seemed expensive to me.

I imagine they have quite sophisticated stuff inside, like a grey-coded disk
or inductive coils.

I'd like something cheaper, e.g. for amateur telescopes.

I wondered if it would be possible to shine (or reflect) a LED through a
disc of polarising material, then pass the light into a pair of photosensors
with similar polarised material with the polarisation angles at 90 degrees
to each other.

As the shaft rotated through 360 degrees, the light through each photosensor
would vary
(ideally in a rectified sinusoid form, but in practice it will differ).

The ratio of signals from the two sensors (w.r.t. the original beam)
would indicate the absolute angle 0 to 90 degrees.
You would need a way to tell which quadrant you were in of course.
Perhaps three sensors at 60 degrees to each other for a 3-phase system.

The advantage would be that it should be fairly cheap to make, because you
don't need a precision gray-coded disc or whatever. If the light beam is
shone over a large enough polariser area, then small defects have less
effect.

The disadvantages include having to compensate for whatever non-linear
response the sensors give, and imperfect 60 degree alignments, but I'm sure
this can be solved by a little ingenuity. Perhaps some analogue
conditioning, then a digital calibration look-up table. But I suspect that
the polariser and electronics would be cheaper than using precision
mechanical parts.

If Winfield is the co-author of The Good Book (The A of E) then I am sure he
will have valuable comments on telescope shaft encoders.

 

Thatz really great, infact i was able to get good idea and enough info
for my design.

Thanx friends,
karthik bala guru