All Sky Camera

[Gina]

Here are a couple of photos of the solenoid and shutter drive mechanism.

[Gina]

With everything put together and the shutter drive working, I found I've got things the wrong way round for my shutter design   So I'll have to redesign the shutter - not a big problem

[Gina]

Here's a screenshot of the SketchUp model of the solenoid and shutter drive mechanism 3D printed parts.  The lever that's operated by the solenoid has a projection on the side of the boss to take an extension coil spring to pull the shutter into the closed position (with Baader film to reduce the sunlight to a safe intensity and allow daytime imaging).

[Davey-T]

I have a Minitron mono camera that I was thinking of rigging up for meteor watch but could leave set up permanently it has AGC  which is annoying when trying to image the Sun as it refuses to let me over expose anything, wonder if it would be OK to point directly at the Sun, would it just dim itself ?

Dave

[Gina]

I have a Minitron mono camera that I was thinking of rigging up for meteor watch but could leave set up permanently it has AGC  which is annoying when trying to image the Sun as it refuses to let me over expose anything, wonder if it would be OK to point directly at the Sun, would it just dim itself ?

Dave

Probably but there is still a danger of the focussed sun burning the image sensor and causing permanent damage.  This is not bound to happen and there are some sensors that are supposed to be able to cope with the full intensity focussed sun light without sustaining damage.  The ZWO MSI120MC and MSI120MM cameras are supposed to be "sun safe".

As for auto brightness function, I tried this with the QHY5 and PHD2 but it was a total failure in daylight.  Whenever the sun was in the frame it shut the exposure right down and only a bright point appeared in the image.  When the sun wasn't present it just racked the exposure up until everything suffered whiteout   For nighttime imaging it needed the exposure time set to the maximum of 15s anyway.

[Davey-T]

If it's pointing straight up it should never get full direct Sun, even in midsummer or does the fisheye lens overide this ?

Dave

[Gina]

Yes, the fisheye lens give views right down to the horizon.

This image was captured just as the sun was setting.

[Gina]

Here is the proposed method of reducing the holding current for the solenoid.  When off, the electrolytic capacitor is charged up to the full 13.8v.  Then when the power MOSFET is switched on the full 13.8v is applied to the solenoid, gradually decreasing as charge is taken out of the capacitor until the current supplied through the 100 ohm resistor causes the capacitor voltage to stabilise at a much lower value.

For this to work the gradually decreasing daylight and and hence current in the light dependent resistors has to be read by a switching (Schmitt trigger) circuit so that the switch on of the solenoid is virtually instantaneous.

[Gina]

Next I need to decide how to implement a Schmitt trigger circuit.  This could be with an op amp chip or with discrete components.  Have to see what bits I've got   Not short of power MOSFETs - IRFZ44N type as I used for controlling Peltier TECs and dew heaters etc.

[ollypenrice]

A little before midnight this is what our Robotic Allsky is showing;

Now check out that point of reddish light pollution just a tad north of east on the horizon. OK, let's not get excited about it because it isn't going to affect us - but there is an irony attached to it. It comes from the village of Lagrand which is the home village of none other than Roger Bonnet, former director of the European Space Agency. (Name dropper, me? Never!  ) Hehheh, but it's true.

I'll keep this screen grab because tonight a certain mad Irishman and I completed a four year run on our present project. He pulled out the Champagne, in fact, but now we are at it again on the Ha. No rest for the wicked. We're all mad...

Olly

[Astroscot2]

That tree really ruins your horizon Olly. Nice sky..

[Gina]

I'll probably use an op amp for the Schmitt trigger as it uses fewer components.  So this would be the circuit diagram.

[ollypenrice]

That tree really ruins your horizon Olly. Nice sky..

Don't panic, only the robotic scopes see it. It isn't there for the humans! 

Olly

[perfrej]

And one of said robotic scopes bagged 11 hours of data  of undisclosed objects under that sky 

A bit after midnight we passed the "light meridian" and are now headed towards shorter nights . We had clear skies until 22:30 up here too so I got over 6 hours of data from the balcony - until 22:30 First reasonably usable images rolled in at about 16:00 from the CCD Autopilot controlled balcony obs. This is after a record November with 5 HOURS of sunshine total in the Stockholm area - obviously with clear night hours in the same numbers.

Sorry for the off topic... Gina, you should use a small stepper instead. Grab one out of a broken ink-jet printer Schmitt triggers are nowadays available in single device small three pin packages! No need to play with analog stuff...

/per

[perfrej]

Olly is actually wrong about who can see our new allsky. http://grinderphoto.se/Full_etoile.jpg

/per

[Gina]

Sorry for the off topic... Gina, you should use a small stepper instead. Grab one out of a broken ink-jet printer Schmitt triggers are nowadays available in single device small three pin packages! No need to play with analog stuff...

/per

No problem Per   Not really off topic anyway

I did think of using a small stepper motor but the only ones I have ATM have built-in gearboxes so no fail-safe facility.  I'll probably have another look at my recycling stuff when I'm better.  Not just broken printers but also VCRs, floppy drives, CD drives etc.  However, a stepper needs more electronics than a solenoid   OTOH the mechanics are certainly easier and probably better.

I did wonder if Schmitt trigger devices were available as a simple single package but a Google search didn't find any   I do know that the 555 chip has a Schmitt input but not sure if that's any easier than an op amp and 3 resistors.

[Gina]

Found this light sensor module on ebay that would simply do the daylight detection.  But if I were to use a stepper motor I'd need an Arduino  (or ATMega chip) so could use an analogue input with LDRs and resistor.

[Gina]

There are a number of these opto detectors with a digital output that might replace the LDRs and Schmitt trigger eg. this one

EDIT - Oh no itisn't! datasheet

Hmm...  need a different search phrase I think.  Just coming up with IR detector devices that output a modulated carrier wave signal

Dratted seasrch engines get on my nerves at times

Getting bogged down here   Maybe it's time to move on to another project

AAAAAAAAAARRRRRRRRRRRRGGGGGGGGGGGGGGGGGHHHHHHHHHHHHHHH!!!!!!!!!!!!!!!!!! :eek: :eek:

[Gina]

Oh dear - looks like this project has ground to a halt until I can get/find some bits   I have ordered some op amps TL071 TI JFET OP AMP DIP-8 IC's TL071CP Texas Instruments which will take a few days to arrive and which should enable me to do something later.  Not really ideal but unless I can find something in my boxes that will just have to do.

I'm sure there ought to be light detectors that have a digital output but I'm darned if I can find any

[Davey-T]

Perhaps you could butcher, modify one of these.

Dave

http://www.qvsdirect.com/400-watt-thermal-photocell-switch

[Gina]

Now that's what I call overkill

[pete_l]

I'm sure there ought to be light detectors that have a digital output but I'm darned if I can find any

An LDR fed by a pre-set pot wired to the input of a 4093 Scmitt trigger logic gate should do the trick. Though in practice, you'd probably want some hysteresis in the detector output. So I guess you'd be looking at 2 LDRs scmitts and presets - one for the "on" threshold and another one for "off". Feed them into an S-R latch to trigger your actions.

[Gina]

Yes, something like that

[Gina]

Made up a test rig to check that the pulse solenoid idea works.  Found a 68 ohm 10W resistor (didn't have 100 ohms at 2W), 4700 microfarad capacitor and push button switch.  Connected to a 13.8v supply.  It works fine - pressing and holding the push button caused the solenoid to pull in and hold.  The holding current was 180mA.  Releasing the PB released the solenoid (of course ).   Initially I tried a 1000 microfarad capacitor but that wasn't sufficient.

[perfrej]

No problem Per   Not really off topic anyway

I did think of using a small stepper motor but the only ones I have ATM have built-in gearboxes so no fail-safe facility.  I'll probably have another look at my recycling stuff when I'm better.  Not just broken printers but also VCRs, floppy drives, CD drives etc.  However, a stepper needs more electronics than a solenoid   OTOH the mechanics are certainly easier and probably better.

I did wonder if Schmitt trigger devices were available as a simple single package but a Google search didn't find any   I do know that the 555 chip has a Schmitt input but not sure if that's any easier than an op amp and 3 resistors.

http://www.mouser.com/ds/2/115/74LVC1G17-80223.pdf

This is the one I use for reset delay in my arduino compatible projects.

It's €0.24 in single quantities

/per