Electronics!

About the control circuit of the motors, I found that I'm in a serious lack of knowledge.

What I'm trying to say is, the "3 way switch" which I mentioned before should be a SPDT (single pole double throw) switch, and with a single DPDT switch, we can already form a H-switch to reverse the direction of a motor.

So, all I need now is a DPDT relay to read autoguiding signal, and to convert it to real motor power.

DC geared motors arrived

They arrived, the sender is from Hong Kong, and that explains why the shipping is cheaper than quoted (which is to US).

They're very small, less than 1 inch long (exluding the output shaft), the gears are metal, and the gear box are made of brass.

I shall test them out tonight when I have time. I believe these are perfect candidates to do motorized focusing work, given they're small and powerful, and with suitable RPM at 6V.

--

Phrase one of the project will be to make a manual guiding box, here's the list of things to do:

1. shaft coupler to connect the 3mm shaft of the motor, to the 6mm shaft of the TG-SP II

2. M1.5 screws to mount the motors to a board

3. a plastic board: to drill holes there to mount the motors, the power supply and the circuits boards

4. 3-way switches, to make the dual motors controller box

Maybe the plugs and cable from my old indoor wireless phone can serve as the connection from the controller box to the motor units, since it has four wires inside. :-)

--

This piece of hardware seems to be very useful for autoguiding:-

http://www.pc-control.co.uk/motorbee_info.htm

It uses a USB port (HID type), can control two DC motors for bi-directional movement or four DC motors for single direction. External power supply can be used to drive the motors, or I guess it's also easy to put the power from the USB port to power the motors. PWM is used to control the motor speed as well.

Sounds too much like the shoestring controller... it's tempting for me to check mine.

The price is inexpensive at 28 british pound. It's cheaper than to buy a ST-4 USB adapter, and it also makes the wiring simpler. All I will need to do is to write a ASCOM driver.

20071230 Sun

It's cloudy today, we see no sun basically, but a bright circular patch of light can occasionally be seen through the cloud.

With my 10x30 IS and the newly made Baader solar film cell, I can see there's no sunspot on the sun.

The moving cloud gave an impression of that something is moving, but it's dead silent, indeed.

Summary of Purchase in 2007

Magazines or forums love to put some hot products in the beginning of a new year, and for here, I will put on a summary of items which I have purchased in 2007, in the order of which I can recall from my memory, most likely being most used:-

1. Borg 45ED II with JMI NGF-S:- this is the top of the list, I use it nearly twice every week, and I bought it to a trip (not astronomy oriented), and it's so compact, high quality and useful!

2. Coronado PST (for its etalon):- this is the most exciting project which I've implemented all those years, it makes the most powerful and the most economical setup for H-alpha imaging

3. Canon 10x30 IS:- A 30mm binoculars for astronomy?! Yes, I didn't make it wrong. Image stabilizer is a magic, it makes 10x truely useful without a tripod, the image is so bright and you will soon forget that it's just a 30mm, I love this one, it helps me to see Comet Holmes in urban center, while I'm very busy with my family and studies.

4. TIS DBK 21AF04.AS:- I must be crazy to buy the color version too, but I really love this camera. It quickly gives me the best Jupiter image which I've ever taken. Believe it or not, it takes better image with my C5 than my ToUcam Pro with my C8 (now sold). To be fair, indoor imaging does not allow me to exploit the potential of a C8 fully, but for my C5, it's fine enough. From entry 1-4, you see that I'm really optimizing my small setups. Small scope, small etalon, small binoculars, small camera.

5. APM Herschel Wedge:- this is used far less than the above, but it's not the problem of itself, but it's due to the fact that it's solar minimum now. White light had a hard time during solar minimum, and somehow I also owe my Herschel Wedge a bigger refractor.

6. Baader CaK:- basically same fate with 5, but narrower bandwidth does the work to show more detail, however, since this one is not really too narrow, sometimes I'm too lazy to bring it out, but sure not after solar minimum.

7. C mount lenses (wide angle):- this is the workaround before I go for a DSLR, those TIS cameras can do some limited deep sky works, especially when I'm locked at home with no dark sky, they do their job very nicely, especially considering the price.

8. Shoestring astronomy FC-USB:- this is actually more like for my remote solar scope project, which is suspended due to the lack of the suitable location.

9. Meade DSX mount:- again part of the remote solar scope project.

10. f/6.3 SCT reducer:- this is nearly not used at all, but I'm not blaming it at all, since I don't have time to really do deep sky imaging yet.

Other than off the shelf stuff, here's a list of DIY stuff which comes from my mind in no particular order:-

A. A USB power cable for my TG-SP II:- I found despite the TG-SP II wants 6V, it can be powered by a USB port, and I've tested that it still tracks accurately.

B. Peltier cooler for my DBK/DMK:- nothing special but just to cool the cameras, for better long exposure performance.

C. Solar filter for my Canon 10x30 IS:- sometimes ago I bought a 25mm pocket monocular with baader filter to look at sunspot whenever possible, but I found the image quality is less than desirable, this one is really way better and with IS, even small sunspot can be shown.

H-alpha: the big guy and the small boy

The first one is a Gitzo G106, with a Takahashi TG-SP II, Borg 45ED II. Coronado SM40/BF10 is used, and a DMK31AF03 is used for imaging. The PST etalon module can be placed in front of the BF10 for narrower bandwidth.



Next is a C5/PST based system. The tripod is a Gitzo G1415, with a Meade LXD55 mount, the scope is a Celestron C5. A Cheapy-ERF is placed in the front of the C5, a PST etalon and a BF10 is used at the rear port. Again, a DMK31AF03 is used for imaging.

Inside the C5/PST setup

The first component is the ERF, usually, people will use the C-ERF from Baader but it's pretty expensive. Instead, I used a big red aerial lens filter which I call it a Cheapy-ERF for its cost is something like $20-30 USD shipped! Mine has 6.5" clear aperture, and I've made an adapter to mount it on my C5 with the help of a local folk.

The ERF is used to filter out unwanted light, in this specific case, only red light will be passing through it. There is no guarantee that there will be no signal leakage, i.e. it could contain green and blue light, UV/IR could pass through too. This is just a very preliminary filter to reject some unwanted energy. It's particularly important for my C5 based setup, since if you let unfiltered sunlight into it, the baffle tube can get burnt, the secondary can be damaged as well.

I found that the sun at prime focus after the ERF is still quite hot, if a C-ERF is used, the image stay cool, and that's the C of C-ERF means. However, with the Cheapy-ERF, the image at prime focus is good enough.

I tried to use a CaK after the Cheapy-ERF and I got nothing, that means the Cheapy-ERF is quite effective to remove other light than red.

Since the light after Cheapy-ERF is still strong, it could cause internal reflection, so I added some soft padding to tilt it up slightly, most of the internal reflection issue is solved.



Next is the PST etalon, basically, the heart of the whole system. An etalon will filter light to enable ultra-narrow bandwidth, like in this case, at around 1A to show prominences and surface detail in H-alpha. The PST etalon can be tuned like the rest of the solarmax filter, there is a collar ring to let you adjust. And the PST etalon has a setup of afocal lens to make light parallel before going into the real etalon, and then to converge light again for viewing/imaging. H-alpha, and its harmonics will pass through the etalon.

A 1.25" nosepiece is made to insert into the rear port of the C5, and a 1.25" visual back is made to let us use a blocking filter there.



Finally, after the cheapy-ERF and the etalon, only H-alpha light and its harmonics will pass through. So to filter out the harmonics, we use a dielectric H-alpha filter and it's the blocking filter. Its bandwidth has to be narrower than the distant of the H-alpha light and its first harmonics.

20071226 Sun

Very silent sun, just got a few small prominences. C5/PST is used. Transparency like 7/10, seeing very low at 2/10 at best.

1216 (GMT+8):-


1218 (GMT+8):-


1219 (GMT+8), the most beautiful prominence today, still small and simple:-


1223 (GMT+8), a random patch of the sun:-


1225 (GMT+8), a random patch of the sun, this setup is not really good at surface detail:-

Solar filter for my Canon 10x30 IS

Just made a solar filter for my Canon 10x30 IS.

The cell is from heavy paper board, and the filter material is from Baader. Since the Canon 10x30 IS is pretty small, I made a single cell for both aperture at once, actually, those materials are left after making a filter for my C5. Since the filter material is for both objectives, it's big enough to be used in a standalone manner, like a solar eclipse shade.

The 10x30 IS is very small, and so I can also hold the filter in place by hand to further secure the snap-on attachment, it adds a sense of security therefore.

With the relatively good magnification of 10x, and the image stablizer, I guess it's going to be a great tool for me to have a quick look to see if there's any sunspots, before I setup my SM40/BF10, or even the C5/PST setup.

20071225 Merry Christimas Sun

It's cloudy today, but there were some rare cloud gap. Seeing very bad at 2/10 at most, transparency from 6/10 in large cloud gap and 0/10 for most of time.

SM40/BF10/Borg 45ED II, DMK 31AF03:-

1434 (GMT+8), prominence and surface detail in one shot:-


1435 (GMT+8), optimized for prominences:-

Small tasks

Finished the "mechanism" to fix the Peltier cooler on the DMK/DBK, now it can be removed and attached in a matter of seconds. I think that I will use the cooler more often from now on, especially for longer exposures.

Also tried to use the JMI motorized focuser controller to control a simple DC motor removed from a toy car, and it can be used without any problem, however, since that motor is designed to run fast, lower voltage will not move it, I guess it only start moving from 6V and move fairly fast at 9V full.

Then I disassembled an old remote control too look for suitable components to finish my dual axis fine control/autoguiding motor project, it seems like not very useful.

Guiding signal

Disclaimer: the following are very preliminary designs and they're not suppose to be free of problems, and instead, it should have problem, so don't follow them unless you're 100% clear about what you're doing. The author will not be responsible for any problem directly or indirectly caused by the information here.

To control the motor with the guiding signal inputs, one can use a circuit like below:-



If Vcc is applied on dec+, the motor will turn in one direction, but if Vcc is applied on the dec-, the motor will turn in the other direction.

The above circuit can be integrated with the last one for manual control, but notice that those buttons should not be pressed if autoguiding is used.

Notice that dec+/- should be from a relay, not from the guiding signal itself.

It's very cloudy now, probably no chance to take any solar shot today.

--
Additional remarks on 30/Dec/2007:-

I did an experiment as a test of concept, it works, but the resistor has to be chosen carefully. If it's too low, the current will be large enough to kill the resistor really easily. If it's too high, the current drop will be too large to stop the motor from moving at all.

Therefore, the "internal resistance" of the motor has to be measured first, and then we shall calculate the maximum resistance which will not stall the motor (in series), but still large enough to reduce the current in order not to burn the resistor.

Controller hand box design for DC Geared Motors

Disclaimer: the following are very preliminary designs and they're not suppose to be free of problems, and instead, it should have problem, so don't follow them unless you're 100% clear about what you're doing. The author will not be responsible for any problem directly or indirectly caused by the information here.

DC Geared motor can be reversed by changing the polarity of the inputs, and its speed can be controlled via varying input voltage or PWM. To changing the polarity of the inputs, a simple design can be used like the following:-



It consists of two buttons, each has three inputs, when the button is pressed, the top input is connected to either one of the other inputs, and if the button is released, it will be connected to another inputs.

A (variable) resistor can be connected in the position of the red ellipse, to control the voltage applied.

Suppose the left button is pressed and the right button is released, the green lines are connected and the red lines are disconnected. Therefore, output A will be -ve and output B will be +ve.

Suppose the left button is released and the right button is press, the red lines are connected and the green lines are disconnected. So, in this case, output A will be +ve and output B will be -ve.

So, you see, by pressing different buttons, the polarity is reversed. For example, a motor is connected to it, and the shaft is connected to the DEC knob of the mount, pressing one button will turn it CW and the other one will turn it in CCW. Therefore, to duplicate the about circuit in RA, we will then have control over RA adjustment as well.

This simple setup will allow motorized manual guiding, but it's hard to incorporate into a autoguider port.

6V 10rpm Mini DC Geared Head Motors

Just ordered two from ebay, the seller said they're new, for less than $30 USD shipped, it's a nice bargain.

Specifications:-

Typical: 10 rpm @ 6V
Shaft: 3mm dia. shaft with fix screw notch
Size: 10mm x 24mm ( no included shaft) length
Reversible by changing polarity
Mounting: M1.5 x 2 screw
All metal gears

For the relatively slow speed, they will be good for motorized focusing, or autoguiding. I shall try to locate two suitable shaft coupler, to connect these 3mm shaft to the 6mm shaft of my TG-SP II.

Mounting would probably be a simple plastic plate, the controller box will need to design and implement, I hope this box will allow manual guiding by pressing buttons, or by an autoguiding port through a computer.

20071218 Last bit of sun light

Seeing 2/10, sun near "horizon", transparency 3/10, 978 was gone.

1639 (GMT+8), surface detail:-


1640 (GMT+8), prominences, false color:-


All by Borg 45ED II, SM40/BF10, DMK 31AF03.

20071215-1216 Geminids

Even more cloudy, nothing was captured in that 7.5 hours continuous recording. This time, I tried another way to mount the camera, so that the field of view is even wider (mount a ball head in a TG-SP II wedge), again same setup and setting as on the first night. The cloud looked funny, two layers basically, the upper one was floating from an opposite direction to the lower layer.

20071216 Solar observation

Good bye 978, so much cloud today but with patience, we could still catch a few shots. Borg 45ED II, SM40/BF10, some close up are done with a 2x barlows and the last one is taken with a PST etalon to bring the bandwdith to ~0.6A.

1511 (GMT+8), full disc, surface detail:-


1512 (GMT+8), full disc, prominences:-


1516 (GMT+8), 2x barlows, AR978:-


1524 (GMT+8), 2x barlows, AR978:-


1531 (GMT+8), 2x barlows, AR978:-


1540 (GMT+8), PST etalon, full disc surface detail:-

20071215 Sun

Seeing is great at 6-7/10, transparency is like 3/10. AR978 is alive and kicking after one week, and it's really huge in size. C5/PST with DMK31AF03.

First shot is the sun at prime focus of my C5 with ERF fit in the front, there seems to be featureless but with a suitable camera, great feature jumps out:



1309 (GMT+8), AR978:-


1312 (GMT+8), hey... I told myself, Shark? em..


1314 (GMT+8), this is a funny shape prominence!


1315 (GMT+8), another shot of the above prominence, alternative coloring scheme:-


1317 (GMT+8), close up of AR978:-


1335 (GMT+8), another close up of AR978:-


I hurt the index finger of my left hand, rather seriously... when I checked if the ERF is secured or not, it really slided out and my finger is pressed in between the heavy ERF and the corrector cell... it's now pretty bad and still pain after nearly 6 hours.

20071214-1215 Geminids

DBK 21AF04.AS, Cosmicar 2.3-6mm at 6mm, f/1.4 wide open, ~8.5s each frame, 7.5 hours from first frame to the last. Nothing except cloud apparently.

Peeping into the motorized focuser controller

I just open the controller box, actually, it's not anything special because you will have to open it to replace the battery inside, which is a 9V alkaline, I found the expiry date of the battery is like 2006, so I know this focusing motor is very energy efficient!

Back to the topic, I found that controller is surprisingly simple. It's basically to provide DC to the motor directly from the battery, with a simple resistor in serial, and also a variable resistor, which is just to control the speed of the motor. The two (directional) buttons do the job about swapping the polarity of the DC to the motor.

I'm sure the motor inside the focuser is just a DC geared motor. So, my direction is correct to find similar offering. That is, a small DC geared motor having low RPM, and then I will have to build a controller box similar to this focuser controller box, but it will have two ports, one for RA and one for DEC.

And then to add a ST-4 like autoguiding port there.

Re-collimation needed during imaging?

Last time when I'm taking images of the sun, I found need I need to re-focus after taking images for 10 minutes or something like that, the OTA under direct sunlight, will expand and cause the focus position to change.

Now, I wonder if the collimation need to be fine tuned as well? It seems logical to say yes.

However, it's next to impossible to do with the sun, since an ERF is installed in the front, and it blocks the collimation screws.

So, maybe collimation at night time is the only way to go.

Autoguiding a TG-SP II

It seems like a 6RPM Geared DC motor will do the job, it's available from the internet, it's speed depends on the input voltage, and it makes the control circuit a very simple thing, and so making it to use with a ST-4 style control would be asy.

So, the only problem now is to really buy one, and to mount it on the place of the slow motion knobs.

Seems not a hard project, let's see. It's definitely a high priority project when I've time.

To shop list:-

1. shaft coupler: to connect the motor with the slow motion control knob shaft (~6mm)

2. solid state relay: to control the on-and-off of the motor, maybe it's not required? can be powered via the ST-4 signal? is it electrically safe?

3. of course, the motors

Lunt Solar Systems in Tucson

1. Single Pass Front Mount Etalon System:-

50mm without central obstruction
0.75A (single) or 0.55A (double stack)
With blocking filter for up to 600mm focal length

The best thing is the price... just around a PST!!!

2. Single Pass 60mm with Internal Etalon System:-

60mm telescope with internal module (not just a filter)
0.8A

Just a little bit more expensive than the above.

3. Single Pass 60mm Calcium K line Filter System

Similar to above, but for CaK (internal module)
2.4A

Again, around the price of a PST!

Spaceweather

Got a link to my image of AR978, here's part of the screen shot, showing my name there:-



And here's the picture which I've submitted:-



Just an record.

On TG-SP II modification again

This is to follow up the modification idea which comes up into my mind earlier this year:-

Idea earlier this year

basically, to make it GOTO will be pretty impossible, since the RA part cannot be cleared in 360 degrees. However, to make it dual axis autoguide-able is still possible. The simplest solution is to add to motors to control the RA and the DEC slow motion knobs, like what I said in the earlier post, by adding a motor there like a motorized focuser to the RA and DEC knobs, it's basically done. ST-4 style signal can be applied to the motors in form of relay signals. No modification of the original circuit is needed as well.

I measured that the shafts are around 6mm.

And I also found a good source of motor, like that from the UK vendor of a system called PFocuser, they can sell nice and light weight motor units alone at moderate cost. At around $100 USD, I could get two motors shipped to my home.

So, the last part is to make a ST-4 style socket to control these two motors, I guess it could be done relatively easy. So then with a Shoestring adapter to output ST-4 style guiding signal, everything will be ready.

So, it's the lighest GEM with autoguiding capability. Let's see.

20071209 Sun (AR978)

So much cloud today! But I got a short time window, managed to get a couple of shots in H-alpha and one more in CaK, Borg 45ED II, SM40/BF10, one with a PST etalon or APM Herschel Wedge + Baader CaK. Seeing was 3/10, transparency also 3/10, with so much thin and thick cloud floating around and they really hurt the contrast, anyway, just an record. AR978 is still going strong, and 977 is around the limb, about to disappear from our view.

1511 (GMT+8), full disc H-alpha:-


1513 (GMT+8), 2x barlows, 0.7A:-


1518 (GMT+8), 2x barlows, PST etalon added to get ~0.6A, notice that the QRF on the top left is far more contrasty:-


1523 (GMT+8), APM Herschel Wedge, Baader CaK, 2x, different wavelength, totally different appearance:-

20071208 Sun (AR977 and 978)

We got some real active regions finally. Seeing is very poor at 1-3/10, transparency also bad at 4/10.

The following shots are taken with Borg 45ED II, SM40/BF10:-

1245 (GMT+8), full disc surface detail:-


1246 (GMT+8), full disc prominence:-


1247 (GMT+8), 2x barlows, 977 with a nice QRF on the left:-


1249 (GMT+8), 2x barlows, the prominence on the right of 977:-


1251 (GMT+8), 2x barlows, AR978:-


1252 (GMT+8), with 2x barlows, AR978 close up, false color:-


1252 (GMT+8), with 2x barlows, AR978 close up, same as above but in b/w:-


The following two are taken with Borg 45ED II, APM Herschel Wedge plus a Baader Ca-K:-

1259 (GMT+8), full disc:-


1304 (GMT+8), 3x barlows:-


The following shots are taken with C5/PST:-

1314 (GMT+8), AR978 close up:-


1321 (GMT+8), the prominence on the limb near 977:-


1322 (GMT+8), AR977:-


1326 (GMT+8), AR978:-


1328 (GMT+8), AR977 close up:-



More images pending.