Fixing a dull ‘Personal Solar Telescope’


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A decade or so ago, I bought a brand-new Personal Solar Telescope from Hands On Optics. It was great! Not only could you see sunspots safely, but you could also make out prominences around the circumference of the sun, and if sky conditions were OK, you could make out plages, striations, and all sorts of other features on the Sun’s surface. If you were patient, you could tune the filters so that with the Doppler effect and the fact that many of the filaments and prominences are moving very quickly, you could make them appear and disappear as you changed the H-alpha frequency ever so slightly to one end of the spectrum to the other.

However, as the years went on, the Sun’s image got harder and harder to see. Finally I couldn’t see anything at all. And the Sun got quiet, so my PST just sat in its case, unused, for over a year. I was hoping it wasn’t my eyes!

I later found some information at Starry Nights on fixing the problem: one of the several filters (a ‘blocking’ or ‘ITF’ filter) not far in front of the eyepiece tends to get oxidized, and hence, opaque. I ordered a replacement from Meier at about $80, but was frankly rather apprehensive about figuring out how to do the actual deed. (Unfortunately they are now out of stock: )

I finally found some threads on Starry Nights that explained more clearly what one was supposed to do ( ) and with a pair of taped-up channel lock pliers and an old 3/4″ chisel that I ground down so that it would turn the threads on the retaining ring, I was able to remove the old filter and put in the new one. Here is a photo of the old filter (to the right, yellowish – blue) and the new one, which is so reflective you can see my red-and-blue cell phone with a fuzzy shiny Apple logo in the middle.

This afternoon, since for a change it wasn’t raining, I got to take it out and use it.


It works great again!

The Unknown History of the Telescope, by Roger Ceragioli

Fascinating article about how the origins of the telescope are not quite so clear after all. (Pun intended!)

(EDIT: Roger wanted me to emphasize that he doesn’t think he has the final word on this history. Later, I’m going to try to make his graphics more visible, too. Looks like WordPress has changed how you add photos again!)

More on the Origins of the “Telescope.” LONG!
From: Roger Ceragioli
Date: Mon, 25 Jul 2022 21:30:48 EDT

Greetings again.  The Galilean telescope is a peculiar beast optically.  Part of the reason it was the first form of telescope was that it gave an erect image, using only two lenses.  But because there is a particular third optical element (the human eye) involved, we need to consider the total sytem (convex objective, concave eyepiece, human eye) to understand what may have happened in 1608 as well as in the decades prior.

And so in this email, I want to review some aspects of this “bionic” system.  Part of what has, in my opinion, afflicted the debate over the origins of the telescope is lack of attention to the nature of this total bionic system.  

Now, it is, of course, hardly conceivable that if the first eyeglasses came into use around 1295 AD, using convex lenses to treat long-sightedness (presbyopia), and concave lenses came into use around 1450 to treat myopia, for 150 years no one bothered to experiment with placing different types of lenses together to find out what would happen.  As I mentioned previously, we read in Fracastoro’s book, Homocentrica (a book on planetary theory) about the marvelous effects of putting one convex lens on top of another.  Apparently this means directly on top of one another, and not at a distance.  Still it shows that people were putting lenses together in the 16th c.

Giovanni Battista della Porta in 1589 mentions combining a convex with a concave (ie. the essence of an early telescope), and that if you know how to do it right, both nearsighted and farsighted people can see clearly.  So I would propose, not that he “invented” the telescope, but that he took a step forward and invented a kind of variable focus low power two-lens eyeglass system.  It could have been constructed as follows:


Pay no attention to the title of the slide, when it says “Galilean-Type Refractor.”  Instead, notice the magnification: 1.25x (a VERY low power), and how the device is constructed.  You have on left a 4-diopter (10-inch focus) convex lens, good for old people to do close-up work.  And on left a 5-diopter concave, good for strongly myopic people.  You do the viewing from right to left through the eyepiece, placing your eye’s pupil as shown.

Now, part of the reason why eyeglass lenses can be optically quite terrible and work just fine, is that in daylight the eye’s pupil closes down to about 2 or 3 mm in diameter.  In the dark at night it opens to 5, 6, 7 or even 8 mm, depending on age, to let in more light.  The above diagram assumes 2 mm.  The blue, green, and red lines passing from left to right represent NOT colors of light, but different ray bundles coming from differing directions out of the graphic on left.  I.e. different field positions.  Blue is on-axis, green is 2 degrees off-axis, and red is 4 degrees off-axis.  The bundles all converge on the eye’s biological pupil and are focused onto the retina.

What’s important here is that in this sytem, the eye’s pupil becomes the delimiting factor in determining how much light enters the eye from each object point.  By one definition of magnification, 

Magnification = Diameter of Entering Bundles/Diameter of Exiting Bundles in a telescope.  

By measuring the bundle diameters we derive the magnification.   So, for example, if you have a 200 mm telescope mirror, then the entering bundle is 200 mm in diameter.  And if the exiting bundle is only 1 mm in diameter after it comes out of your eyepiece, then we can say that your telescope’s magnification is 200x.  In the diagram above, if the magnification is 1.25x and the bundles of rays passing out of this “telescope” and into your eye are each 2 mm in diameter, then by the equation the bundles entering the objective must by 2 x 1.25 = 2.5 mm.

So in the above system, the objective lens doesn’t need to be any better than a common eyeglass lens for the viewer to find the (barely magnified) scene perfectly sharp.  It would, therefore, have been easy for Della Porta to make the above device and have it work just as he says.  In 1609, when asked, he sent the following rough sketch: 


Crude, but it sure looks like a telescope.  The “c” tube “trombones” in and out to focus.  By this stage 20 years later, Porta was sneering at the device and calling it “crap.”  Crap in the sense that it was amusing, but had little effect on “making things nearer.”  With my 1.25x version above, the length of the device would be about 100 mm.

The image quality (assuming decent glass) would be perfect all over the field:

Here the colored dots do represent colors of light.  The black circles represent the size of the Airy disks.  Since the dots for the three sample colors (486, 546, and 656 nm representing the visual spectrum) all fall well within the black circles, we can surmise that a viewer using the system will see everything sharp.  The device is only of interest in showing the basic geometry of a Galilean-style refractor, and in that it can focus to varying distances, from infinity to about 2 meters.  Anyone can use it, since like a telescope no matter what the state of your eyes (nearsighted or farsighted) you can refocus.  But the magnification is hardly noticeable.

Now, if you try to increase the magnification, then the difficulties arise.  Let’s say we replace the eyepiece with one that magnifies to 6x:

Here I have stretched the drawing vertically by 5x versus reality to make the paths of the rays for different field positions clearer.  The first thing that’s happened is that because of the 6x magnification, now the entering bundles are 2 x 6 = 12 mm in diameter!  For each field position, the entering rays cover much more of the objective lenses surface now, just as in a real telescope.  But, indeed, this IS now a real telescope! 

The result is that any appreciable defects in the objective lens WILL degrade the image.  If the glass is of low quality in transmission, or if the lens surfaces are not very spherical, they will blur the images, just as the objective in your childhood “Trashco” telescope used to do.  It is these problems that Rolf Willach rightly pointed to in his book, The Long Route to the Invention of the Telescope.  But there are still more that he did not discuss.

Because in this type of optical system the “pupil” (ie. where all the ray bundles intersect) as at the eye, and there is a lot of refraction far away at the objective lens, you will inevitably get “lateral color” in the images:

Here we have a spot diagram for the 6x system.  On-axis we’re ok.  But off-axis at 0.125 and 0.25 degree (the true field of view is now much smaller than before), the red, green and blue bundles are decentered from one another.  That means that stars will be seen stretched and smeared, ie. very unsharp.  Also, on-axis we now see longitudinal chromatic aberration, although not bad.  This system won’t work well as a telescope, because most of the field of view will be smeared.  It is this effect (as well as any smearing from surface figure error or glass inhomogeneity) that Lipperhey needed to correct.

He did so, it appears to me, probably by imposing a diaphragm on his objective lens.  We don’t know this for certain, but it is very likely, as Willach first suggested.  Now, the important part to understand is that if the objective diaphragm makes the bundles of rays exiting the eyepiece smaller than the eye’s own pupil, then what Lipperhey really did was to transfer the pupil of the bionic system from the human eye to the objective lens (where it should be for a telescope).  This transference instantly sharpens images in the outer field:

The system layout and raypaths now look like so:

The entering bundles all intersect at the objective and diverge where the eye pupil goes.  So we get much sharper images, with much reduced chromatic effects, but at the cost of a narrow, very narrow field of view.  Galilean telescopes are infamous for their narrow fields of view.  You have to “scrunch” your eyeball up against the eyepiece glass and move it side to side to see as much field as possible.  This is inevitable given the optics.  And it all gets worse in general as the magnification increases.

If you want to reach even 20x or 30x, it’s necessary to make the telescope longer and longer, to mitigate the chromatic effects.  My 6x system above is only about 400 mm long, similar to terrestrial telescopes seen in early images.  But for an astronomical telescope, magnifying 20 or 30x, you might need triple or quadruple of that.  With triple or quadruple of the objective size.  That is 24 or 32 mm.  Galileo’s famous 1610 telescope with which he found Jupiter’s largerst moons, seems to have had an aperture of 38 mm.  It required a mounting (as Galileo advised) to hold it steady.

To conclude, we have a number of other people aside from Lipperhey who claimed to have used a device similar to his before him.  Certainly, Della Porta did in 1589.  And perhaps also, Jacob Metius of Alkmaar, as well as an unidentified “young man” in Holland.  It may be that Raffaello Gualterotti had something like this in Italy, and Joan Roget in Spain, as well as others.  Likely, if these devices really existed, they were of very low power.  Metius admitted that his didn’t work too well.  But the point here is that I think these claims should not all be dismissed as fraud or sour grapes.

We see above why such devices could easily have existed and probably did before 1608.  And yet we also see why they would in general have failed, if their authors tried to increase the magnification.  It required that the system pupil be transferred from the eye to the objective lens, before you could get a functioning telescope of notable magnification.  The reason is not only what Rolf Willach has rightly pointed too (glass quality and surface/wavefront figure), but also because of the underlying optics of chromatic aberration.

The same thing happened in the 1630s, when the Keplerian telescope was adapted for terrestrial viewing.  Its output image had to be inverted and reversed.  Kepler himself had suggested a method already in 1611.  But in practice this led to terrible results, due to lateral color error, smearing off-axis stars.  Let us remember that chromatic aberration as such was not recognized until Isaac Newton in the 1670s.  Before then people had no idea that light is not intrinsically white.  They thought colors were some kind of modification of white light.  But what kind of modification, and how it all worked utterly flummoxed them.  So there was no meand to intentionally correcting color error.  No theory or solutions could exist until much later.  

And so, just as I suspect Lipperhey may have hit upon a solution to his problem through the use of a diaphragm, possibly under the influence of a false (then widespread) theory of how the eye works, so too when Anton Maria Schyrleus de Rheita, and later Giuseppe Campani found the first effective 3-lens terrestrial eyepieces, which completely corrected the lateral chromatic aberration plaguing Kepler’s 2-lens eyepiece, they couldn’t know the true reasons why their systems worked.  Yet work they did. 



Hopewell’s Ealing Mount is Working Again – After 8 Months!


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 Guy BrandenburgJul 6 

 At long last, we have finally got the venerable, massive Ealing telescope mount at Hopewell Observatory working again, after nearly 9 months, with a totally different, modern, electronic stepper motor drive based on Arduino.

My first post to the OnStep group ( ) was on October 21, 2021, over eight months ago. In it, I wrote that I had decided to give up trying to fix the electro-mechanical synchronous drive and clutches on our Ealing-Byers mount at Hopewell Observatory, and asked the folks on the OnStep message boards for help in choosing the best OnStep combination to drive such a mount. 

Since then, it’s been a very long and steep learning curve. We only fried a couple of little slip-stick drivers and maybe one MaxESP board. We got LOTS of help from the OnStep list (not that the posters all agreed with each other on everything)!  We ran into a lot of mysteries, especially when we found, repeatedly, that configurations that worked just fine on our workbench wouldn’t work at all when the components were put into the mount!

But now it works.

Let me thank again in particular:

* Prasad Agrahar for giving me the OnStep idea in the first place by showing me a conversion he had done;

* Alan Tarica, a fellow ATMer, for cheerfully partnering and persevering with me in working on this project for the past 8 months in many, many ways; 

* Ken Hunter for providing tons of basic and advanced advice and a lot of hardware, all for free; 

* Robert Benward for extremely helpful advice and drawings; 

* George Cushing for providing some of the original boards we used;

* Khalid Bahayeldin for lots and lots of OnStep design features;

* Howard Dutton for designing, implementing, and supporting this whole project in the first place; and 

* Arlen Raasch for bringing his wealth of trouble-shooting experience and a lot of nice equipment up to Hopewell, spending full days up there, and saving our asses in figuring out the final mysteries. Among other things, he kluged (by the way, “kluge” is German for “clever”, not clumsy) a level shifter to make it so that the 3.3 volt signals from our MaxESP3 board would actually and reliably communicate with the higher-voltage external DM542T stepper drivers that controlled the very-high-torque NEMA23 steppers, rewiring some of the jumpers on our already-modified MaxESP boards, and making the wiring look professional, and other stuff as well, thus essentially pushing us over the finish line. 

* All of the Hopewell members for supporting this project 

* Bill Rohrer and Michael Chesnes who physically helped out with soldering and wiring work at the observatory.

I plan to write up a coherent narrative with a list of lessons learned, and perhaps I can help make some of the step-by-step directions in the OnStep wiki a bit clearer to the uninitiated. Obviously I’ll need to write a user guide for this mount for the other Hopewell members.

If Alan and I had gone straight to our final configuration, this project would have been quite a bit cheaper. In addition to what’s inside the mount and control box at the observatory, we now have on hand something like this list of surplus items:

* four MaxESP boards in various stages of construction and functionality; 

* a dozen or more different slip stick stepper drivers we aren’t using; 

* four or more external stepper drivers, mostly TB6600;

* five or more stepper motors of different sizes; 

* a hand-held digital oscilloscope;

* lots and lots of wires of many types;

* lots of metal and plastic project boxes of various sizes;

* lots of tiny motherboards; and 

* lots and lots of sets of various mechanical electrical connectors (many were used, later cut off, and then ended up in the trash).

Yes, one does need spares, and yes, lots of this stuff has multiple uses, but this has not been a ‘green’ project. On the third hand, it has been extremely interesting and fun to learn all these new skills.

The final substantive changes that got the Ealing mount up and running were made during the Fourth of July fireworks down in the valleys on each side of the ridge that our observatory sits on. What were the changes? (1) switching the black and white leads from the mains power leads (they original, scavenged, cord had the white lead as Hot!) and (2) reversing the Declination motor direction. It also helped that I was not zoned-out and punchy from lack of sleep, as we had been when Arlen and I had last worked on it.

On July 4th, it at long last worked properly!

This Ealing mount’s original, labeled, built-in manual RA and DEC setting circles make it quite easy to put the scope into Home position before you turn on the power. One just loosens the clutches and moves the axes to 6:00 hours exactly in Right Ascension and 90 degrees exactly in Declination. From there, I found the OnStep system behaves very nicely. It accurately slewed to a number of bright, obvious targets of various sorts on both sides of the meridian. However, when I tried to get it to aim that night at M13, it refused, sending an error message that it was too close to the zenith for safety. And it was (altitude 87 degrees)! Very impressive – a safety feature I hadn’t even known about!

None of the objects that I slewed to was far from the center of the field of view, even when the scope slewed across the meridian. I was using an old, 2-inch diameter 50 mm Kellner eyepiece on an f/12 six-inch aperture D&G refractor.

I found that the Android app to be **much** better for initial setup than the SHC. Arlen, Alan and I all found that setting the correct latitude, longitude, UTC offset and so on from the SHC was a real brain-twister because of its unfortunately not-very-friendly user interface. Using the OnStep app on a cheap, old Android tablet made the whole initialization process very much easier and faster, especially after I let the tablet discover what time it really was from my iPhone’s wireless HotSpot. 

However, I found that the hand paddle is much better for fine-tuning of pointing and so on, because the bright display on an Android, no matter how dim one makes it, will destroy one’s night vision, and one cannot reliably feel where the directional buttons are on a flat screen while staring  through an eyepiece. Obviously, one can feel the buttons on the SHC quite well, maybe even with gloves. A joy stick would be even better…

Alan and I and the  other Hopewell members still have many more OnStep features to learn.

However: if I had known this project would take over eight months of hard work, I think I might have tried fiddling with the original Ealing clutches some more. 

Oh well, we have a mount that has much more capabilities than it ever had, and Alan and I have learned quite a bit of electronics! I’m proud of what we did!

Progress with OnStep re-Build of Ealing Mount

Here are some pix of the progress Alan Tarica, Michael Chesnes, Bill Rohrer and I have made so far on our conversion project for the university-grade Ealing telescope mount’s motor drive at The Hopewell Observatory, with moral support from other Hopewell members.

The project has gone through quite a few different very-low-budget but very-labor-intensive phases.

(We are a low budget organization, and being a retired school teacher, I for one have more time than I have money.)

The first phase involved me trying to re-install the clutches on the original gear and synchronous motor system from the 1970s.

This required careful disassembly and re-assembly of a very complex gear train, which I did accomplish, but I was unable to fine-tune the exact amount of friction needed, so I gave up on that approach and decided to try an electronic conversion that many other folks had been using on their own telescopes.

Namely, an Arduino-based system called OnStep that grew out of the modern CNC industry that powers modern 3-D printers and most modern fabricating machinery of all types.

Our version has MaXESP3 boards made and sold or generously given to us by Ken Hunter and George Cushing. We have also had considerable help from OnStep’s Howard Dutton, Robert Benward, and NCA’s own Prasad Agrahar.

The MaxEsp board (about the size of my hand) powered two little stepper motors (roughly cubical, 5 cm on a side) donated by Prasad. We were given by Ken, and also purchased, some tiny LVL and TMC stepper drivers about the size of a postage stamp that fit into rails on the MaxEsp board. The motors were connected to the wonderful original Byers gears inside the mount by ingenious little direct-drive couplings donated by Prasad.

This rebuild required me to remove all the original motors and gears and clutches in the scope mount’s motor box and carefully line up the new motors with the telescope shaft, which required some careful machining and filing.

We discovered that those stepper motors didn’t have enough torque to drive the mount, even with all of the optical tubes removed.

(Btw, connecting all these electrical components was a huge learning curve for me! There are SOOOO MANY different types of connectors, and we have now discarded several types as unsuitable. Wiring up and soldering some of those connectors require the skills and steady hands of a seasoned watchmaker or Heathkit veteran — which I am not. My hands shake terribly!! One small slip of one of my hands, one time, was enough to fry two of those tiny drivers and blow a tiny fuse… I had to adjust a tiny potentiometer screw while the circuit was live… I didn’t realize there was a better place to connect my grounding lead to… fortunately those drivers only cost a few dollars…)

It was suggested to add a belt and put pulleys of different sizes onto the stepper motor and the mount shaft. That required moving the stepper motors and hence a bit more machining.

But that didn’t work either.

So I ordered bigger stepper motors.

But the first ones I ordered also didn’t have enough torque either! I found I could stop their rotation with my bare hand!

So I ordered some more powerful stepper motors. And got rid of the belts and pulleys. (We have extras if anybody’s interested!)

But they needed more current (amperes) and voltage than the Tiny postage-stamp sized stepper drivers could produce.

Larger stepper drivers won’t fit directly on the MaxEsp board, and also need more voltage than the board can tolerate.

So Ken Hunter figured out a way to bypass that: he changed (for free!) some of the wiring on the back of two of our MaxEsp boards, and suggested some much larger stepper drivers about the size of a small deck of cards, and a regulated switching power supply that puts out a steady, adjustable direct voltage from 0 to 42 volts that is the size of a medium-length hardback novel.

But the MaxEsp board can’t take that many volts, so we needed something called a buck step-down power supply to reduce the 0-42vdc power down to a steady 10 or 12 volts – just for the MaxEsp board.

We wired all that up and re-adjusted the stepper motors and got the worm gear from the stepper motors to mate properly with the Byers gears on the scope mount — not an easy task! Physically screwing in the gearbox was insanely difficult until We figured out an easier way. We only fried two of the buck power supplies via short-circuits, but this was no great loss since five of them had cost about $15.

Everything worked great when we had all the components wired up **outside** the cavities built into the mount itself. But when we carefully slid the five separate components into those cavities, some of the many, many tiny little colored and numbered and labeled leads broke off that connected all those components, broke off.

Yes, we made wiring diagrams — I think we are on version eight or nine now! (Mine are done in pencil on large sheets of thick art paper. Bob Benward has generously made electronic versions for us; I’ll have to send him the revisions.)

We took it all back out, and did some trouble shooting. I tried using an old Heathkit oscilloscope made by the late Bob Bolster (one of the principal founders of Hopewell) but made little progress until Ken explained **where** to connect the o-scope leads (hint: at the output from the MaxEsp board and not at the output from the drivers), and Alan brought in a brand-new solid-state o-scope.

Using that info, and using Alan’s new, more sensitive and easier-to-use o-scope, and taking careful notes, and examining those outputs on the o-scope screen when we try to slew or track with the scope controls, I finally figured out that one of our OnStep boards had some defects, but the other two were ok.

It also became obvious that trying to shoehorn all these components inside the original compartments inside the Ealing mount wouldn’t work. We needed a nice sturdy electrical project box. I didn’t see any at local hardware stores that were large enough, so I ordered a sturdy steel one online. It ended up still being too small, so I exchanged it, and with Alan’s assistance, built standoffs to isolate and secure all the components, and I was able to mount and wire them all up correctly onto a removable steel plate that fits inside the box. It’s all modular, and swapping out components is pretty straightforward. (See the photos below.)

Michael, Alan and I decided to place the box against the north side of the masonry pier supporting the telescope. (Drilling the mounting holes into the concrete ended up being harder than I expected, but we got it done.) We also had to drill holes for the “Liquidtight” flexible electrical conduit that connects the OnStep/Arduino circuitry inside the box to the mount where the motors and gears reside. And holes for the fan and vent. And for the Wi-Fi / Bluetooth antenna. And the USB port.

When I finished wiring up everything, I turned on the power… and…


It turned out that I had done something to the 0-42VDC power supply so that it received 110VAC but put out nothing at all. I was too hot and tired to figure out and fix whatever I did on-site that Memorial Day, so I ordered another one, which should arrive this afternoon.

I’ll connect the new power supply on Sunday.

Here are some pix.

From bottom right, CW: greenish MaxEsp board with three sub-boards; silver-colored 0-42VDC power supply; small dark buck power supply; 2 green-and black TB6600 stepper drivers

The fan and USB jack are on the left. Some of those dangly wires need shortening.

The big electrical project box in position on north side of pier, underneath the optics-less Ealing mount. Those hoses atop the box are not for Slurpees!

I had to stop up a number of the holes I had previously drilled in those panel covers on the mount, to keep insects out. If you don’t, marmorated stink bugs and lady bugs enter in droves and many die.

Our OnStep re-build is at last working!


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For many months, we members of The Hopewell Observatory have been doing our best to repair the 50 year-old clock drive on our university-grade Ealing telescope mount.

Yesterday, after a lot of help from others, I finally got it to work — at least in the day time. With no telescopes mounted on it. And 100% cloud cover. So I really don’t know for sure.

We still need to test it out on a clear night, to see how well it tracks and finds targets.

I think I will re-configure the wiring so that it fits in a box outside the mount, instead of using the weirdly-shaped compartments inside: one needs to do occasional maintenance on the OnStep hardware and software, and none of that is easy to access right now.

A short video is attached.

Problem Perhaps Solved


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I think I have figured out what was going wrong with our OnStep build:

  1. Our unmodified Arduino-based, green, MaxESP3.03 OnStep micro-controller unit board had two major errors: it didn’t put out any signal at all in the Enable channel in either Right Ascension or in Declination, and in Declination, the Step channel didn’t work either. (I can only guess what caused this, or when it happened, but these errors explain why we couldn’t get this particular board to work any more.)
  2. We had the connecting wires between the two blue, modified boards of the same type and the external TB6600 stepper drivers in the wrong arrangement. We stumbled upon a better arrangement that Bob Benward had suggested, and indeed it worked!

I never would have figured this out without the nice hand-held digital oscilloscope belonging to Alan Tarica; his help and comittment to this project; advice from Ken Hunter that it was a bad idea to have the boards and stepper drivers connected, because the impedance of the motors makes the signal from the board too complicated, and also the signals to the motors themselves are extremely complex! Let me also thank Bob Benward for making beautiful and elegant schematics from the drawings I’m making with pencil and eraser on a couple of 11″x17″ sheets of stiff art paper and pointing out the anomalies between our (Ken’s? I thought I was faithfully copying his arrangements….) original wiring connections and what the manual recommends.

I’m puzzled that our earlier arrangement worked at all. Given that this oscilloscope sees extremely complex, though faint, voltage curves from my own body (anywhere!), I am guessing that electrical interference fooled the drivers into sending the correct commands to the stepper motors even though the STEP and the DIRECTION wires were crossed.

In any case, I attach tables summarizing what I found with the same oscilloscope I had in the previous post. I have highlighted parts that differ between the three boards. Boards “Oscar” and “Linda” are basically identical ones, both of them modified to bypass the location where small, internal stepper motor drivers (about the size of the last joint on your pinky finger) are normally held. Instead, these two boards, both blue in color, connect to two external black-and-green stepper drivers about the size of your hand.

Board “Nancy” differs from the other two in a number of ways: it’s green, which is not important for its function but makes it easier to distinguish. It is also an unmodified one, and it carries TMC5160 stepper driver chips pushed into two rails.

I used orange and green to highlight the differences in output.

With electronics: when it works, it’s amazing, but it is very, very fragile.


Edit: It all works just fine on my desk. I hope it will also work once we put it into the telescope’s cavities and wire everything up!

Oscilloscope Testing of OnStep System


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We are still at work trying to debug our OnStep re-build of the venerable Ealing telescope drive system at Hopewell Observatory.

Without having a whole lot of experience with oscilloscopes, we used a brand-new OWON 200-series hand-held unit to measure the output of our various MaxESP3.03 boards towards the stepper motors. We don’t really understand what these waveforms actually mean, and a brief search of the OnStep wiki page does not immediately point me to screenshots of what the signals should look like under various conditions.

In any case, some of the waveforms we see look like simple square wave signals. Some look like weird semi-random combinations of square waves, and some look like just plain noise.

In this first video, we have an unmodified MaxESP3.03 board with TMC5160 drivers, not connected to any stepper motors. I attached the ground pin of the probe to one of the grounding grommets at a corner of the MaxESP board, and systematically probed the pins that come out towards the various windings on the stepper motor. We also pressed N, S, E, and W buttons to see what happened. Here goes:

Those of you who are experts on this: do these waveforms appear to be OK to you in this situation?

This next setup is different. It’s a MaxESP3.03 board that Ken Hunter has modified by adding or moving about ten jumpers on the underside of the board; it has no slip-stick drivers for RA or DEC mounted on the MaxESP board itself. Instead, each axis has three (not four) wires coming out of the same place that four wires generally come out to connect to your stepper motor; these three wires connect to four of the inputs on an external, and separately-powered TB6600 stepper driver, which then feeds four wires to the two coils on the stepper.

The arrangement we have now does seem to work, at least on our workbench at the ATM workshop in Chevy Chase Community Center in NW DC, as you can see and hear in this video, but, once again, neither Alan nor I have any idea if the waveforms are correct. Here is the video:

Again: experts — do you think those waveforms are correct?

We were surprised at how complex, and apparently noisy, are the signals on the Step and Dir lines from this modified MaxESP board to the green-and-black external TB6600 drivers. They don’t show up at all in these two previous videos, but they will show up in the next one, which I’m having a bit of trouble uploading at the moment.

In that video, I test both RA and DEC output.

In RA, pin #1 is Enable and is apparently not connected to anything. It produces a wave that looks like a crosscut saw seen from above that has teeth very widely spaced apart. That ENA signal doesn’t change no matter what buttons we push; we think the graph is merely showing interference from something or other.

Still in RA, pin #2 is the STEP pin, and it produces a nice square wave that changes dramatically in frequency when you press the E or W buttons on the SHC. We don’t really see the difference between the E or W graphs.

Still in RA, and in contrast, the graphs for both the Dir and GND pins seem to just look like noise. When one presses ‘E’ the noise graph from the Dir pin definitely changes voltage (it drops off the screen), but not when we press ‘W’. Nothing happens to the noise graph on the fourth pin (GND), no matter what we do.

On the DEC side, all pins seem to put out flat but noisy signals. The noise signal on Pin 2 (Step) moves dramatically but identically lower when you press either the North or South button on the SHC. The noise signal on Pin 3 (Dir) does not change when you press buttons, and neither does the noise signal on pin 4 (GND).

So can we conclude that this board is fried?

Birds and City Lighting: a Toxic Mix


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An alarming article about studies of bird deaths due to bright city lighting. A couple of quotes:

Every 11 September at dusk, in memory of the 2001 attacks, New York City mounts the Tribute in Light, an art installation in lower Manhattan. And every year, as twin towers of light bloom skyward, they attract thousands of migrating birds, sucking in warblers, seabirds, and thrushes—along with predators such as peregrine falcons eager to take advantage of the confusion. On each anniversary, bird conservationists wait below, counting and listening to disoriented chirps. If the observers report too many birds circling aimlessly in the beams, organizers flip off the lights.

In recent years, on-site observers have also used a complementary tool to quantify the orbiting birds: weather radar, which bounces off birds as well as raindrops. In 2017, a group led by Cornell University ornithologist Andrew Farnsworth found that during seven previous anniversaries, the once-a-year installation had attracted a total of about 1.1 million birds. Within 20 minutes of lighting up, up to 16,000 birds crammed themselves into a half-kilometer radius. But when the lights flicked off, the dense clouds of birds on the radar screen dissipated just as fast, a finding later confirmed by on-site thermal cameras.’

Later, discussing a single building, the author found that a

‘key factor was how many of the convention center’s windows had been illuminated. Each individual bright window left more dead birds for volunteers to find the next day. The correlation suggests halving the number of lit window bays would halve the number of bird strikes, the team estimated, saving thousands of birds at this one three-story building. “It really does seem that each window makes a difference,” van Doren says.’

Mysterious OnStep Behavior


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We are still trying to get our venerable, university-grade Ealing mount to work properly with its new OnStep motor drive system. We thought we had – at long last – everything set up perfectly and running correctly with the various components wired up properly but not yet pushed into place in the interior cavities of our mount. All seemed to be working well until we pushed the last components and wires inside, and then closed the hatches.

Then things stopped working.

We soon figured out that the force we had to use when moving all those items inside the mount had broken some of the leads. We found those broken leads and replaced them with shorter ones.

When we started it up again, we discovered that the mount would not ‘track’ to the west in right ascension — something that the software and hardware are programmed to do as soon as the system is turned on. In fact, I couldn’t slew it to the west either. Eastwards was no problem. Also, we could only slew southwards, not northwards.

We didn’t know what to do, so I emailed a followup question to the wonderful folks at the OnStep wiki. Several folks thought we had a balance issue or a limit switch issue, but I went up today to check on the balance — and concluded that’s not the problem. We have no limit switches yet either in hardware or in software. So that’s not it, either.

Wondering if we had somehow screwed up the MaxESP3 board that is the heart of the OnStep system, I unplugged the board (and all of its sub-boards, as a unit) we had been using last weekend, and plugged in a duplicate board, built by Ken Hunter and ‘flashed’ by him with the same Config.H file as the other one.

Listen to the screeching!

This weird behavior is not the same weird behavior we were getting with the other OnStep MaxESP3.03 board. What on earth is going on?

Another suggestion is that we may be creating ground loops by not connecting our wiring properly. I don’t know. I wish I had taken some electronics classes during my time in college. It would have come in handy here!