Cheap optical encoders, idea for DIY

[bojan]

While thinking about some better and cheaper way to make a good and high resolution encoder for my EQ6, among many similar components and products I found this one, from US Digital:
http://usdigital.com/products/aedr/ (http://usdigital.com/assets/general/168_aedr_datasheet.pdf)

This contact-less, optical reflective sensor requires just a printed stripe pattern on a white background (could be done by laser printer on paper) in a form of tape (that can be wrapped around shaft) or round circle, and I can have a cheap encoder with very high resolution, that can be used with Ek box or equivalent.
For example, 75 lpi (lowest resolution sensor) is ~3 l/mm, this is easily printable with moderate laser or ink jet printer.
10cm (33mm dia) will have 90 strips per rev, this is 360 tics/rev with Ek's box!
Of course, there is no limit to this: thicker the shaft (or wider wheel around which the paper tape is wrapped), higher the resolution. The higher resolution configuration chip (212 lpi) will have ~1000 tics/rev.
For 10,000 t/r we need a wheel 30cm in dia, quite reasonable for any dobson mount.

There is really no need to spend k$ for off the shelf encoders, when something like this is available for couple of bucks.

I will try to get samples and build a prototype, and I will report results here when I am finished.
The expected cost for any resolution encoder with this sensor is around $10 each.. (Because paper tape with printed pattern costs nothing).
Food for thought for astro equipment manufactures ;)

[DavidU]

I have been looking at encoders grom an older ball mouse

[bojan]

Yes, those sensors are OK, but they require transparent wheel (or tape). Vishay has them, here: http://www.vishay.com/docs/84756/tcut1300.pdf
I was after reflective type, they are a bit easier to make.. also the one I found is higher resolution (3x or more).

EDIT:
Actually, I am using those encoders you mentioned (from old mouse) on my Bartelised Dobson..

[bojan]

There is also a similar product from Avago :
http://sensors-transducers.globalspec.com/datasheets/18/AvagoTechnologies/8BA8AA78-2EA7-4682-BC78-D2E6D77A7724
with even higher resulution (obtained by interpolation - 30/u or 1440l/mm!)
It would be interesting to find magnetic encoder, similar to the one used for electronic gauges and calipers.. they also have to be cheap (considering a caliper cost $20 .. this is the cost of metal work only).
And the resolution!!! 0.01mm means, 33mm dia will have 10,000 ticks/mm.

[DavidU]

http://www.pepperl-fuchs.com.au/cps/rde/xchg/SID-40DBD099-A5AB4A0B/australia/hs.xsl/8879.htm?rdeCOQ=SID-64E55FFB-F1F68F7C

[kinetic]

Here's my go at it:

http://www.iceinspace.com.au/forum/t=420201 (http://www.iceinspace.com.au/forum/showthread.php?t=42151)

[bojan]

Finally, working on the bench, with Bobson's Ek box :thumbsup: (Thank you Bob for your patience!). The deep red LED is barely visible.. at 17mA current it is not much of a sight - because it emits very close to IR part of the spectrum...
What took so long were PCB's... not that they are complicated.. I combined them with some other projects I am involved with at my friend's company, and there were other priorities.. so I had to wait.
Today I managed to get hold of them and mounted two US Digital modules, and tried the whole thing with shiny strips, and it works.

The next step is proper encoder tape (printed on white paper) and experiment on my dobson..

[bobson]

Good on ya mate! I knew you gonna make it work. Correct me if I am wrong but those encoders have to be mounted on PCB?

My EK's box works perfectly, thanks to you. You keep the other one for experimenting. I am looking forward to see how it goes on your dob.

bob

[bojan]

Yes, they are actually SMD integrated circuits, containing LED and detector encapsulated in clear plastic which also serves as lens.
I was thinking of having them mounted on wires at first, but this is risky.. it is better like this. We are not in any hurry ;)

[DavidU]

Bojan, you had those PCB's made?
Excellent work by the way.

[DavidU]

Are these Agilent AEDR-8300 SMD's?

[bojan]

No Dave, they are US Digital
http://usdigital.com/assets/general/168_aedr_datasheet.pdf
however they are the same (212l/i, I also have Avago SMD's, obtained from Farnell, almost the same price, http://au.farnell.com/avago-technologies/aedr-8300-1w2/reflective-opt-encoder-2ch-212lpi/dp/1735258?Ntt=173-5258).


PCB's were made by Speedy Circuits, I just send them the design :-)

[bojan]

The test with line pattern on white paper was not successful... the reflectivity of the ordinary paper for laser printers is not adequate.

Now the next stage is to try the line pattern printed on shiny substrate... gloss paper perhaps..
I am not giving up on this one..

[DavidU]

You can Laser print tracks on Aluminiumized paper.
http://www.amazingpaper.com.au/cat/index.cgi/shopfront/view_by_category?category_id=439

[kinetic]

Don't forget the iron on property of the laser toner Bojan.
As I found with the PCB making, even if you're printout
becomes just the transfer medium, use it to iron/transfer to
the substrate that works maybe?:shrug:
Watching with interest, best of luck mate :thumbsup:

Steve

[bojan]

Thanks for ideas guys.. going to Officeworks now...

[bojan]

Print on glossy paper did not work either..

BUT - printout on overhead projector foil, placed over shiny aluminium plate (as a background reflector) did work !!! :thumbsup:

So, it seems I have a workable solution.... I just have to do a proper design now.
For vertical axis of my dobson it will be a round circular encoder pattern at the lower side of the drive wheel (like CD player, so it does not collect dust on the pattern), for horizontal axis it will be either a tape placed on the edge of the hor wheel, or again circular pattern (~120° sector only) at the inner side of the wheel, I am not sure yet what is better.

This encoder can be used in conventional way as well: transparent disc carrier with separate LED on other side (in this case build-in LED is not used) however this complicates the design a bit..

A quick calculation:
For 25mm diameter wheel (and no additional up-gear) , and 3 lines/mm pattern I have 9425 tick/rev, which is 2.3 arcmin resolution.
More than enough for my bartelised dobson. And all for ~$15 and a bit of tinkering.. which is a great pleasure and fun per se.

A real poor man's Argo Navis ;)

[DavidU]

Excellent solution Bojan.

[kinetic]

Hi Bojan,

just another idea,
If you ever wanted to give away the reflective method and use
the interrupted window method like I use then you still could make
a viable optical disc.

You could print your incremented pattern out on a disc as a negative
and etch away the holes where the counts are.
Put your photodetector pair either side of these windows and try that.
For mine, luckily, I had a purpose built one with 144 slots but I can't
see why a rogue like you couldn't build one. :)
I used a Gaugemaker program to make my index wheel printout.
This great little program does any increment gauge in any
circumference value from 0-360 degrees.
You can adjust the increment fonts, line width, length etc.
Here's the link:
http://forums.x-plane.org/index.php?app=downloads&showfile=6359

Pic 1 attached is a rough printout I used for my index wheel.
Pic 2 is the optical wheel type you would ultimately etch
if it ever worked. This pic is my Dec axis encoder with mouse guts
for photodetectors.

Steve

[bojan]

Steve, I like rogue ides :-)
I will certainly try something like this (just signed in x-plane forum).