Arduino Focus control and Cloud sensor

[Reggie]

looking around the net, I see others heating the sensor too, I still have reservations about putting heat sources hear an IR sensor, as they, rather predictably measure temperature, none that I've seen using a heater have offered up any explanation as to whether it will affect things, so it either does and they are unaware, or it doesn't and they think it's too trivial to mention

[George]

The only thing it might alter is the ambient reading.

[Komet]

Thinking about it, ambient temp is only important if you are also using the output for focus control(I think) or if you are using a traffic light system in software where the difference between ambient and sky temps is used.

However I just watch the sky temp as that is all the info I need whilst actually imaging. It is so sensitive it tells me when conditions have changed even if I can't see any difference visually. I only use it when I have the gear running - I sit inside and control the obs via VNC so sky conditions changing is very useful info.

The thing is I don't think ambient is that important if its a few degrees out. Could be wrong and please correct me if I am wrong.

Anyway I now have a couple of resisters running slightly warm off of a 12v supply in the box and we'll see what happens. I think I might have to go a bit warmer yet. We'll see.

[George]

Well our SGL cloud sensor does work on a traffic light system but once you know how much its being altered by the heaters you can compensate with the software, also any dew point would be affected by ambient.

One way round it would be to pull the ambient from another source well away from any heating.

[ncjunk]

I replied on the yahoo group but heating the box slightly wont have too much of an effect.

The heat is radiating away from the box so i imagine it cant pick much of it up. We are detecting infra red and not detecting heat by relying on a change in the eletrical properties of a sensor due to the heat acted on it from its surroundings. The sensor is effected by ambient heat but the sensor has a "normal" temperature sensor on board which reads the ambient temperature of the device and performs inbuilt temp compensation. I suppose this is because the properties of the detecting material vary somewhat due to temperature.

Of course heating by a couple of degrees wont matter....though i would say heating it by 30 or more should be avoided as that may make a difference, who knows?.

I plan on sticking a couple of resisters in mine as well.

I suppose any heat could only be detected if reflected back into our ir sensor or if it heats an object in front of the sensor that then radiats back.

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[Komet]

Thanks Neil ....

Well I have a couple of 300ohm resistors running off of a 12v supply and it is running about 1.5 degrees above ambient at the moment. That said the dew point is quite low this evening - last night was totally different so whether the amount of heat I have at the moment will be adequate I won't know until I get a wet night.

One interesting point. I had to keep the heater board ( a small piece of veroboard with two wires and two resistors) well away from the sensor as that caused the display to flatline (no data) a lot.

Also the SGL display software after running does not let my Netbook shut down at all ..... any thoughts?

[Euan]

The only thing it might alter is the ambient reading.

The Aurora is a completely heated board because of the this and the rain sensor. It does make the ambient +17 degrees even when it's -2 outside

However, the sky temperature reads perfectly and works great so you have nothing to worry about when heating these things.

[ncjunk]

Thanks Neil ....

Well I have a couple of 300ohm resistors running off of a 12v supply and it is running about 1.5 degrees above ambient at the moment. That said the dew point is quite low this evening - last night was totally different so whether the amount of heat I have at the moment will be adequate I won't know until I get a wet night.

One interesting point. I had to keep the heater board ( a small piece of veroboard with two wires and two resistors) well away from the sensor as that caused the display to flatline (no data) a lot.

Also the SGL display software after running does not let my Netbook shut down at all ..... any thoughts?

When you say flatline does it get any values back ie is the comms working or is it the case it is disrupting the coms?. I am thinking the comms between the arduino and the ir sensor and not the pc arduino comms.

Is the cloud sensor software remaining in tasks when you close it and causing the shutdown problems?

I'll have a look when i can but i start work this week and blumming typical i have come down with a cold...not a good first day today.

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[Komet]

ie is the comms working or is it the case it is disrupting the coms?. I am thinking the comms between the arduino and the ir sensor and not the pc arduino comms.

Is the cloud sensor software remaining in tasks when you close it and causing the shutdown problems?

I'll have a look when i can but i start work this week and blumming typical i have come down with a cold...not a good first day today.

I will do a few tests and get back to you. You take your time ... its not critical at all.

On to Dew Busting. My low heat resistors did not work once I hit dewpoint last night. I did spot this though .... Heating film 47 X 60 mm 12 V CA. 3 W - Heating foils - Conrad Electronic

Hmmmm

[Komet]

Is the cloud sensor software remaining in tasks when you close it and causing the shutdown problems?

There are three instances in Processes. If I close all of them then the machine will close down normally.

[Reggie]

Nice find Komet on those heat pads, I wonder if dobsonian or newtonian scope owners could find a use for those? there's a nice 174mm one, I wonder if there are bigger?

[Komet]

Nice find Komet on those heat pads, I wonder if dobsonian or newtonian scope owners could find a use for those? there's a nice 174mm one, I wonder if there are bigger?

I take it that one of those would work quite happily from a standard Dew Controller?

If so -----

[Reggie]

It would seem so, it looks like it's only drawing 250ma, so not sure if it's man enough, I know normal dew tapes draw around an 1000ma full on depending on size, although that's spread out in a strip, this is in a more concentrated space possibly. looking at the 174mm round one, it's pulling 1.167amps, so that seems like it's more than adequate.

[OzDave]

Hi,

Sorry I've not read this entire thread yet (I'm working my way through) and so the answer I seek might already be written somewhere.

I'm thinking about building myself a motorised focuser and have a couple of questions about the motor.

Firstly, I'm looking at a motor with 400 steps/rev, or 0.9 degrees per step. It can supply a torque of 58 oz.in., which seems like it should be enough, although I'm not sure when a draw tube could be loaded with a camera and so forth.

The motor in question is this one:

Stepper Motor - Sparkfun

I am planning to attach this to a Moonlite CR2, perhaps on the side with the single knob (not the dual speed side), although I've not made up my mind there yet.

Will this motor have enough torque to properly turn the focuser axel?

Will I need any gearing to reduce things further, or will I get enough resolution with the 400 steps (0.9 degrees)?

Sorry if these things have been answered many times. I'll try and seek answers as I read more of the thread.

Regards,

David

[ncjunk]

David,

sorry for the delay replying..

The motor looks ok but if you are planning on using it with an easydriver then take note that it has a current rating of 1.7A and the easy driver only provides a maximum current of 750ma.

I bought the following:-

Stepper Motor with Cable - SparkFun Electronics

I use the above 200 step 1.8 degree motor using microstepping on the easy driver to give 1600 steps per revolution on my ed80. This is sufficient to achieve a good focus but I feel more steps and hence a higher resolution would have been better.

On my C11 I bough a geared stepper, I forget the ratio, which provides 28800 steps per revolution of the focus shaft. the total travel is 64000 which on the c11 provides excellent resolution and focus.

Both configurations have been tested with the following attached:-

ART285 camera

ATIK Filter wheel,

QHY6 camera

TS OAG

I had some problems with the ED80 until I tightened a few screws and adjusted the current a bit.

This is the geared motor I have:-

Motor paso a paso con reducción, protegido con vinilo y con torretas - Lunático Astronomía

it gives 3600 steps per rev and 28800 with microstepping.

So:-

Will it have enough tourque? not sure but probably

Will it have enough resolution? depends what your scope is. if its an ed80 then Yes.

Do I need any Gearing? Yes if you can afford it.

The best motor to get in my opinion would be something like the one I am using on the c11 which is geared and has 3600 steps per revolution. (See above link to lunatico website)

Another option would be to use a pully configuration onto the focuser knob.

I havent answered your questions very well but if you can find a cheap geared stepper then that would be best otherwise a nice pully arrangment would be the next best option.

Let me know if you have any other motor posibilities and what your scope is.

Neil

[OzDave]

Thanks Neil. I've been thinking about a gearbox or pulleys but I started worrying about backlash and how that would affect a focusing app.

What is your experience with backlash? Is it a problem? Do the gearboxes have a lot? The ones I've seen say max backlash of around 1 degree, which seems a lot.

David

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[OzDave]

While waiting to see what replies I'd get, I went ahead and ordered some components. Looks like I've ordered the same Sparkfun motor that you specified Neil. I may need to get a gearbox to go with it by the sounds of it.

I also ordered this driver board, which looks like it has the capability to drive motors needing more power, although the one I've bought initially doesn't seem to need much.

Stepper Motor Driver Board

Finally I've ordered a couple of Arduino Nanos to play around with. One I will use to experiment with the focuser, and the other to muck around with generally. I might have a go at the cloud sensing stuff when I get more time.

I saw another thread on SGL where it was mentioned that the critical focus region can be computed using some formula for which a link was posted. Using the formula, the poster worked out that for an f/6 scope, the critical focus zone is about 60 microns of draw tube travel. Therefore, I think I need to work out the zone size for my scopes and then try to measure how many steps it takes to move the draw tube a known distance. From there I can determine if I've got sufficient resolution to properly sample the critical focus zone. I guess this varies a lot depending on the focuser mechanism.

Regards,

David

[Komet]

CLOUD SENSOR UPDATE (just so as those who are only into the auto focus don't have to read it)

Well I now appear to have lots of controllable heat in the sensor box.

I have fitted one of THESE mounting the IR sensor as close to it as I can. I have covered the element in 3mm neoprene for insulation and am running it from a spare channel on my dew controller. I am getting an ambient temperature reading off of the sensor of about 14 degrees at the moment with the actual external temperature at about 2. This shows a variance of about a degree plus or minus which isn't bad. The dew controller is under half power.

It looks promising - just need a lot of dew now. I'll keep you posted.

[Komet]

Addendum to the above regarding the foil heater element.

This works perfectly from a dew controller and gives variable control against dewing. I like mine.

[ncjunk]

David, not been able to keep up with your progress as i've been ill and busy! Hows it going?

Komet, looks good so the heater elemet is keeping the dew at bay?

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[Komet]

Komet, looks good so the heater elemet is keeping the dew at bay?

Oh yes ..... I can get the ambient up to over 20 degrees c if I want. Its running warm at the moment (actual air temp is -3.6 as I type this) but will cool down when the temperature plummets.

Untitled Web Page

[yesyes]

Interesting.... I never get sky temperature readings that low. The very lowest I had so far was -25. I usually consider the sky clear enough when it gets below -10.

[Komet]

Interesting.... I never get sky temperature readings that low. The very lowest I had so far was -25. I usually consider the sky clear enough when it gets below -10.

The lowest I have had has been just shy of -43. Brr!

[yesyes]

I have a feeling that I have a building or a tree in the FoV of the sky sensor that makes it appear warmer than it is...

[OzDave]

Hi Neil, I'm still waitung for my ordered parts to arrive so no profress yet. Any day now though....

David

David, not been able to keep up with your progress as i've been ill and busy! Hows it going?

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