Sextant digitized

[GeoSound]

Am thinking about building an electronic sextant that would provide near
centimeter accuracy. This would mean a degree should be partitioned to
about 400,000 steps. Was considering using a pot and 5v to feed an A/D
but on reflection think that a single turn pot would not be clean enough
for that many steps. Would someone confirm this for me. Use of a
multi-turn pot requires gears which would be too expensive due to their
very critical meshing needed. Thanx, Ron

 

[PeterD]

On Thu, 12 Jun 2008 13:07:45 -0700, GeoSound <logicon@zipcon.net>
wrote:

Am thinking about building an electronic sextant that would provide near
centimeter accuracy. This would mean a degree should be partitioned to
about 400,000 steps. Was considering using a pot and 5v to feed an A/D
but on reflection think that a single turn pot would not be clean enough
for that many steps. Would someone confirm this for me. Use of a
multi-turn pot requires gears which would be too expensive due to their
very critical meshing needed. Thanx, Ron

None of this makes any sense at all. 1 CM where? 400,000 steps how?
Accuracy? (Undefined, right?) You want cheap, then ask the Chinese to
create it for you.

 

[GeoSound]

400,000 digitized steps in an A/D!
Accuracy to measure down to the centimeter!
Don't need someone else to do it just if my thinking is reasonable!
Education is a curse

 

[John Fields]

On Thu, 12 Jun 2008 22:13:36 -0700, GeoSound <logicon@zipcon.net>
wrote:

400,000 digitized steps in an A/D!
Accuracy to measure down to the centimeter!
Don't need someone else to do it just if my thinking is reasonable!
Education is a curse

---
If education is a curse then you must be blessed.

For 400000 steps, pinhead, you'll need a 19 bit ADC.

Have you not heard of the Global Positioning System?

JF

 

[default]

On Thu, 12 Jun 2008 13:07:45 -0700, GeoSound <logicon@zipcon.net>
wrote:

Am thinking about building an electronic sextant that would provide near
centimeter accuracy. This would mean a degree should be partitioned to
about 400,000 steps. Was considering using a pot and 5v to feed an A/D
but on reflection think that a single turn pot would not be clean enough
for that many steps. Would someone confirm this for me. Use of a
multi-turn pot requires gears which would be too expensive due to their
very critical meshing needed. Thanx, Ron

Use an optical encoder to provide a pulse train - that's going to cost
too

Gears don't need to mesh perfectly - they can be "anti-backlash"
styles. Look them up. A pair of identical diameter gears on the same
hub both engage the pinion gear and are pushed apart slightly with a
spring - ensuring that there is zero backlash - one gear face on each
gear is engaging the pinion gear at all times. They were used in gear
tuning systems in communications receivers.

One assumes you want to be looking through the eyepiece while this
counter thingee reads the angle off the sextant?

Perhaps the trick would be to take an off the shelf digital micrometer
or caliper (very cheap with high accuracy) and somehow work that into
the sextant scale.


--


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[default]

On Thu, 12 Jun 2008 13:07:45 -0700, GeoSound <logicon@zipcon.net>
wrote:

Am thinking about building an electronic sextant that would provide near
centimeter accuracy. This would mean a degree should be partitioned to
about 400,000 steps. Was considering using a pot and 5v to feed an A/D
but on reflection think that a single turn pot would not be clean enough
for that many steps. Would someone confirm this for me. Use of a
multi-turn pot requires gears which would be too expensive due to their
very critical meshing needed. Thanx, Ron

Another idea - a old time variable capacitor. The position of the
knob is directly proportional to the capacity - and that can easily be
resolved into a lot of counts by counting an oscillator's frequency.

Look into VFO ("variable frequency oscillator") amateur radio
operators use them in home built receivers - and they have various
schemes for digitizing the outputs.
--


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[default]

On Thu, 12 Jun 2008 22:13:36 -0700, GeoSound <logicon@zipcon.net>
wrote:

400,000 digitized steps in an A/D!
Accuracy to measure down to the centimeter!
Don't need someone else to do it just if my thinking is reasonable!
Education is a curse

You can do whatever you want - if you want a degree resolved into a
million steps you just have to figure out how to do it.

Check out LVDT's Linear Voltage Displacement Transducers (or something
close to that) it is a whole science of precise small distance
measurement - and lots of off the shelf solutions. The stuff is
relatively easy to build too once you know the theory.

Another cheap and dirty idea is to use an optical potentiometer - a
diffused light source opposite a diffused light detector (photo
resistive element) in between the two is a mask with a long triangular
cutout. As the cutout moves from one extreme of its range to the
other, it varies the amount of light allowed to pass from emitter to
detector. Typical photo resistor might be 10 ohms in bright light and
5 meg ohms in darkness.

Want to get really fancy? a small laser - moving mirror - beam
splitter and you can resolve down into the nanometer range with
constructive and destructive interference.
--


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[caveat]

"default" <default@defaulter.net> wrote in message
news:1213400540_8606@isp.n...

On Thu, 12 Jun 2008 13:07:45 -0700, GeoSound <logicon@zipcon.net
wrote:

Am thinking about building an electronic sextant that would provide near
centimeter accuracy. This would mean a degree should be partitioned to
about 400,000 steps. Was considering using a pot and 5v to feed an A/D
but on reflection think that a single turn pot would not be clean enough
for that many steps. Would someone confirm this for me. Use of a
multi-turn pot requires gears which would be too expensive due to their
very critical meshing needed. Thanx, Ron

Another idea - a old time variable capacitor. The position of the
knob is directly proportional to the capacity

Not always true.

- and that can easily be

resolved into a lot of counts by counting an oscillator's frequency.

Look into VFO ("variable frequency oscillator") amateur radio
operators use them in home built receivers - and they have various
schemes for digitizing the outputs.
--

The problem with a variable capacitor is that it can "drift" with
temperature and humidity changes.

Many years ago,1990's, I worked for a company that produced LORAN-C
receivers and they could, in the experimental models for the military,
locate you to within a foot or less if they could tune in 20 to 30 towers
but I have never heard of anything available to the public that can locate
you to within a centimeter. At that, they used state-of-the-art Cesium clock
generators and racks of clasified high-tech stuff. But, then I was never
allowed in to the section of the building where the government security
cleared Ph D's worked.

I don't believe that you can create a device that will, reliably, position
you to within a cm or two from simple publically available components, be it
GPS, LORAN or Sextant.

 

[default]

On Fri, 13 Jun 2008 22:46:40 -0700, "caveat" <caveat-lector@cox.net>
wrote:

"default" <default@defaulter.net> wrote in message
news:1213400540_8606@isp.n...

On Thu, 12 Jun 2008 13:07:45 -0700, GeoSound <logicon@zipcon.net
wrote:

Am thinking about building an electronic sextant that would provide near
centimeter accuracy. This would mean a degree should be partitioned to
about 400,000 steps. Was considering using a pot and 5v to feed an A/D
but on reflection think that a single turn pot would not be clean enough
for that many steps. Would someone confirm this for me. Use of a
multi-turn pot requires gears which would be too expensive due to their
very critical meshing needed. Thanx, Ron

Another idea - a old time variable capacitor. The position of the
knob is directly proportional to the capacity

Not always true.

- and that can easily be
resolved into a lot of counts by counting an oscillator's frequency.

Look into VFO ("variable frequency oscillator") amateur radio
operators use them in home built receivers - and they have various
schemes for digitizing the outputs.
--

The problem with a variable capacitor is that it can "drift" with
temperature and humidity changes.

Many years ago,1990's, I worked for a company that produced LORAN-C
receivers and they could, in the experimental models for the military,
locate you to within a foot or less if they could tune in 20 to 30 towers
but I have never heard of anything available to the public that can locate
you to within a centimeter. At that, they used state-of-the-art Cesium clock
generators and racks of clasified high-tech stuff. But, then I was never
allowed in to the section of the building where the government security
cleared Ph D's worked.

I don't believe that you can create a device that will, reliably, position
you to within a cm or two from simple publically available components, be it
GPS, LORAN or Sextant.

I'm not really sure what this guy wants . . .

I don't think anyone expects centimeter accuracy on earth with any
global location scheme, least of all a sextant. I'm assuming he just
wants to read a sextant to a high degree of resolution, not
necessarily fix his position to a centimeter with one.

And he's talking about the expense . . .

--


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