I am interested in making my own Digital Setting Circle Computer and have looked at a few threads on the subject. Has anyone checked out this site: http://eksfiles.net/digital-setting-circles/
I have the know how and the tools (yes I have a Pic programmer) to make this unit.
I am after opinions.
Also if anyone needs me to program a PIC I can do that... just pm me.
PIC are quite easy to do now using ICSP programming method. It is cheap and can be done almost anyone. The main issue as seen with other post is the encoders. I personally working on an encoder installation that will be a one size fit most. But it is possible to get encoder setup from Wildcard used for the Argo Navis.
EK Box is a simple kit. I already have a USB interface and am working on a Bluetooth interface which does away with have the circuitry for the current EK box.
I must be missing something but why are you using these expensive encoders for on a PIC when there are much cheaper alternatives?
I definatley would not use friction drives or timing pulleys either - they are way too costly and ugly... the most I would spend on an encoder would be $5 tops and that would be an expensive one!
That's an attitude !
But I am, actually, my encoders cost me $0.00
(they are from old mice, of course), see here: http://www.iceinspace.com.au/forum/a...se.php?a=65266
Timing belts are also $0.00 if pulled out from old printers..
Currently I am working on something more expensive (sometimes a cost is un-avoudable ), and it is from US digital.. not belts, no pulleys, no gears, just contactless optical incremental sensor and some laser printed strips on paper tape. I think it will be according to your taste, despite $7 price tag each
BTW, welcome to the forum
Quote:
Originally Posted by mbirrell
I must be missing something but why are you using these expensive encoders for on a PIC when there are much cheaper alternatives?
I definatley would not use friction drives or timing pulleys either - they are way too costly and ugly... the most I would spend on an encoder would be $5 tops and that would be an expensive one!
The idea that I am working on works with a photo interrupter (Jatycar part no. ZD1901) and a strip printed on a overhead transparency. I was thinking of using a very wide arc to give me greater resolution.
The question is though how many arc seconds do these encoders have to be accurate to? If I am using a push to I wouldn't be able to adjust my scope to down to 1 arc sec.
Only one arcsec is a lot of resolution, you will not be able to avoid up-gearing if you want to achieve this.. And the accuracy will always be questionable..
My scope (with friction wheels ratio 1:20 or close to that) has around 7000 ticks per rot on both axes, which is around 180" or 3arcmin, enough for visual.
The idea that I am working on works with a photo interrupter (Jatycar part no. ZD1901)
This is not going to be easy to use for encoder, you will need more than just transparent pattern printout (additional mask). And, you will need 2 of interrupter modules for each axis (to be able to determine the direction of movement).
Very simple arithmetic shows that for 10,000 t/r I need a wheel (or ~100° sector for elevation) 30cm in dia, quite reasonable for any dobson mount.
And no moving parts whatsoever (apart from telescope itself)
Alternative is this one, but more complicated to use (it needs ADC's): http://sensors-transducers.globalspe...8-D2E6D77A7724
I must be missing something but why are you using these expensive encoders for on a PIC when there are much cheaper alternatives?
I definatley would not use friction drives or timing pulleys either - they are way too costly and ugly... the most I would spend on an encoder would be $5 tops and that would be an expensive one!
It is a matter of preference, My design is quick and easy to configure requires very little effort as I don't have a lot of time ( I mean very very little time). Although as light polution is beginning to bug me in my area, I may have more time available in the near future.
Also mine is designed not to alter the structure of the DOB in any way. I am able to remove all parts and the DOB is completely original.
Some people don't mind drilling holes in there equipment. I do! What I do might sound like a lot but I am able to do lots in small bits of time. I love to experiment it was what I was born to do.
Not sure why you think friction drive is expensive. Mine was quite cheap actually, the whole friction setup only cost me about $30.00 plus the encoder. I haven't finished to whole project yet as I keep running out of time. I am patient though.
I recon both of your systems sound fantastic.
I think I will probably end up buying an encoder if my ideas don't provide me with enough resolution.
I was really wanting to try to design a very low cost system so to help others that can't afford the big bucks.
Slightly off the subject, but I chuckle when I see ppl needing PIC programers and bothering with C and compilers etc. PICAXE PIC basic is free, their PICs absolutely fly at up to 32mhz, one-word hardware interface keywords and literally plug straight into RS232 via the PIC pins for one click download and run, no programmer required. One "count" command is all thats required for encoders and a "serout" to display position on an LCD, no driver code required. And precoded commands to control steppers.
I just read data sheet for your new encoder and have to tell you that one has great potential! That would solve so many problems for dob owners. No pulleys, no belts, no friction drives. Keep us posted how is it going mate. As far as I can see this could work with EK box without any modifications, correct me if I am wrong.
Exactly right, mate
That is why I ordered samples and next week or so there will be some prototyping going on here.
I will certainly posted the results and conclusions here.
The only possibly better solution (from power consumption point of view) would be magnetic sensor (the one used in callipers, with 0.01mm resolution. But I could not source them anywhere.
My Chinese connections are not good enough
Quote:
Originally Posted by bobson
Hi Bojan,
I just read data sheet for your new encoder and have to tell you that one has great potential! That would solve so many problems for dob owners. No pulleys, no belts, no friction drives. Keep us posted how is it going mate. As far as I can see this could work with EK box without any modifications, correct me if I am wrong.
Sounds like you will have a good system Bojan. That sensor that you gave me the specs on is definitely a good option to use with the encoder wheel that I intend to use. to use it without mechanical parts I could print out a large encoder wheel with the required resolution of 4000 tics. If the sensors are easy to source they would be a gold mine.
Ok what I have come up with so far is:
I have pulled a spindle out of an old CD drive - it will be used for the axle to drive my encoder wheel.
I have found to necessary software to make an encoder wheel that everyone can download for free:
GSView and Ghostscript - Postscript file viewer. you can find a version by just Googleing it. You need these programs to view the wheel encoder and print it if you are not a computer nerd like me.
A few old CDs' - Everyone has them!
As far as the optical transmitter and receiver goes I think the cheapest solution is buy savaging an old mouse. That is covered by other posts so I won't mention the process here. the trick with the wheel is that you need to print your wheel on an over head transparency.
The turn ratio will be around 4:1 which is a reasonable ratio as the chance of slippage will be reduced significantly. To make the main planetary friction wheel I was thinking of gluing about 6~8 old CDs' together. using the old CD spindle and CD planetary friction wheel will give me around 5,400 ticks which will do the job nicely.
I will follow up with pictures and more details as the project progresses.
I have made an encoder wheel from an old CD. I printed the code wheel on an over head transparency then laminated it to protect it. I cut the printout in the shape of a wheel then glued it to the CD with spray on contact adhesive. I found an old CD drive I have and removed the rotor part where the CD sits on to spin and what do you know the shaft from the gearbox fitted it like a dream. On the other end of the gearbox I put a remote control car wheel which press fitted nicely. I have also raided a few old mice that I have for the sensors so we will see how they go working with the encoder wheel. oh yea the encoder wheel has 1,000 ticks per rev and the gearbox ratio is around 1:4 (hope I got that around the right way).
I was hoping not to make a wheel with a gearbox but the resolution would have suffered but still it is far cheaper than buying a Encoder so far.
I have actually progressed a bit from what I have posted. I am not particularly happy using a gearbox and having to "hack" a telescope that I will be putting it on (Meade 12" Dob). What my idea now is if I can make a wheel with enough spaces it won't need a gearbox etc which means no slippage. This might mean getting a stainless steel disk laser cut (if the price is right). For the sensors I would be extracting them from and old mouse.
I have been also thinking of connecting a Bluetooth to RS-232 converter from Jaycar (XC4130 is the catalog number) to the Dave EK box so I can use it on my new laptop.
Attached is what I am getting a quote on. I will let you all know the price when I get it.
Also I have got a quote on the MAX232CPE RS-232 level converter:
Sub total: $19.80 - MAX232CPE RS-232 level converter x 5 of them
Freight: $7.50
Total: $27.30
