Lyndhurst Garden House

Lyndhurst Garden House
Lyndhurst Garden House

Wednesday, May 16, 2018

Two Steps Forwards, Two Steps Backward

Yes, I've had another contractor experience, and once again it's the usual Two Step dance.

It's been over a year since I had my Imperial range hood mounted by my carpenter and electrified with a dedicated circuit by my electrician.  Neither would do the job of ducting the range hood to the outside.  They told me I would need to find an "Appliance Installer."  They did not recommend any, but suggest I check with appliance dealers such as places where range hoods are sold.

Last year, I had lined up an "Appliance Installer" through some free internet app.  I called 3 such handymen, and only one returned my call.   Actually this was before I had even ordered the Imperial hood, and at the time I thought I would be installing something much less expensive (which later turned out to be under-cabinet only, not free standing as I had planned, leading me to discover the Imperial and other pricey hoods).  He came out and we simply discussed the issue, he seemed knowledgeable and nice.    I emailed back two months later after I had the hood actually mounted and electrified.  He told me he'd need to come out again to re-do the estimate, which had been based on the cheaper range hood, but he was busy on another job and wouldn't be available for awhile.  Then I went on vacation, and I was tied up with other projects for a month.  Then it was a very hot summer, and I decided to call back in September for this attic work.  Finally when I emailed again, he said he was busy on another job out of town.  That happened a second time in November.

Finally, this year, I decided I need to try someone else.  So this time I went to Home Depot, who does sell range hoods.  Home Depot said they only listed contractors for convenience, and they were screeened, but I would deal directly with the contractor and they would be responsible for all work performed.  I said OK so they gave my phone number to 3 contractors.

One of them called but left no message.  Another never called, as far as I could tell (though I never answer spam calls, so I might have missed).  Finally, the 3rd contractor left a friendly message, so I called them.   They told me a flat rate of $350, and could do the job next Tuesday at 9am.  Later by phone text we changed the appointment to Monday afternoon at 3pm, or earlier.  Texting first, they actually showed up at 1:30.

I showed them the hood with the 7" stub duct which I said was required, and my 7" end cap.  They asked if I had the ducting and I said no.  So they went to Home Depot to get the ducting and other stuff.

They arrived with a reducer which would reduce the piping size to 6 inches.  That would be connected to a ceiling plate, and the ceiling plates were not available in the 7 inch size.  Then, they would fit the pipe to my 7 inch end cap with duct tape.

I said this was unacceptable.  I insisted that the pipe needed to be 7 inches from end to end, it needed to attach to the stub pipe on top of the hood, but could go through the ceiling without a ceiling plate.  So they went back to Home Depot a second time.

This time they did the installation.  I was very unsure about this, but they used "semi-rigid" aluminum piping which Home Depot had said was suitable for "Bathroom and Kitchen ventilation."  I was also unsure about their using Duct Tape, but they insisted it was suitable for ducts.

After the installers had left I decided to check this all out.  I immediately discovered that semi-rigid aluminum ducting is not legal under the International Building Code my city references as the basis for it's building codes.  The code specifically requires ducting with a smooth interior.  It also requires galvanized steel, stainless steel, or copper.  Obviously semi-rigid aluminum fails on both counts.

The building code does not give a rationale, but the issue is discussed on many forums where it is said that if the inside of the ducting has grooves--as all flexible and semi-rigid ducting does--it can build up with enough grease to catch and carry fires.

The code also doesn't specify how the pipes need to be sealed, but in many discussions it is clear that duct tape is unacceptible also.  What is needed is either mastic (reinforced with mesh if covering some area) or aluminum foil tape with UL 181 rating.  Duct tape is not fireproof, and it is not even permitted on fire rated flexible ducts in California.

Here is one inspector discussing all the range hood issues.

Here is another discussion about HVAC in general; cloth tape unacceptible, metal tape or mastic preferred, screws required, it specifices #8 screws.  Also: mastic is generally preferred to tape, should be applied at least as thick as a nickel, 3 screws per duct connection up to 12 inches.

But, are screws OK in range hood ducts?  The above code inspector showed one side screw, most pictures had mastic applied so thick you couldn't see screws, or were marked down because "no fasteners."  The code guy didn't discuss what might be desireable fasteners.  Are clamps OK???

Here's a discussion about range hoods in particular on a San Francisco site.  It isn't official, it's some sort of journalism, but San Franciscans should know; it's a place of a lot of cooking.  They specify using mastic inside before connecting, then screwing with 1/4" screws, the taping with metal tape.

Here's my attempt to link the actual building code for ventilation of all kinds.

Metal tape seems popular.  I think that's because it's much faster to apply.  My concern that it hides the seam, you can never know how good it is.  There may be hidden gaps underneath the metal.  With mastic, you observe the seam itself, which should basically not be visible in the least.  I think this is why building inspectors, and Martin the Energy Nerd, always seem to prefer mastic.  And the code guy above definitely seems to lean that way without saying as much.

However perhaps because the outside gap of a connection may exceed the "1/16 to 1/8" size that must be pre taped, it might be a good idea to simply fiberglass tape each seam first, then apply thick mastic to cover up the tape.



Tuesday, May 8, 2018

Starlab Planetariums

Starlab is a company which still makes classroom sized planetariums.  Designed for 5-meter flexible domes inflated by a blower which is included.  5 planets are included (unlike all "home" projectors ever made).  The price is too high for most homeowners: $13,550.  Adjusted for inflation, the historic Nova classroom projector which included 5 planets would be about the same.

Those older Nova units may have required you to preset the planet positions at the beginning of the nighttime, and then it might simply rotate their sky position as following the earth's rotation.  This would be OK for many purposes, except planetary alignments.

A full calculation of planetary positions is quite complicated.


Wednesday, April 4, 2018

OTA HDTV Antennas

I'm getting almost 60 channels for free.  However, the channels associated with the local NBC affiliate are still affected by "fading."  At first I wasn't getting the station at all.  With the very big and ugly indoor/outdoor Clearstream 2V on top of a china cabinet, I was barely getting the channel at all. Now I have a Clearstream Eclipse mounted to the wall.  In the first mounting position I optimized the NBC affiliate, and it came in strength 80+ perfectly, but then the CBS affiliate was getting constant dropouts.  So I tried to optimize both channels at the same time with a second position.  Now the CBS gets pixelation very rarely, like once an hour.  But the NBC affiliate is getting pixelation about once every 5 minutes.  This is known as "fading" described in this great article.

BTW I live about 5-10 miles from the broadcast tower(s) and they are just about perpendicular to the wall I am now testing indoor antennas on.

Fading can sometimes be assisted by making an antenna more directional.  Here's a homebrew bowtie antenna designed to do this (for attic mounting).  I could put my Clearstream 2V in the attic, but my attic is even more filled with metallic stuff (HVAC plenum and ducts including many return ducts) than the ground floor.




Friday, March 9, 2018

Lighting Protection

This business about antenna lightning safety has gotten me more interested in lightning safety in general.

From what I've read, people are safest inside buildings (and cars) because the lightning tends not to come inside.  However grounding gradients can be created which destroy equipment inside (and that is the purpose of the ground bonding required both for lightning rods AND rooftop aerials).

During storm, you should not be contacting anything wired to the outside, either AC electrical or wired telephone.  Cordless phones are OK.  Plumbing is not safe either.

There has actually been controversy over how lighting rods and similar measures work.  But essentially they direct the lightning currents to ground away from the structure.  Even if the wires themselves don't survive the strike, they will have done their job.

Do lightning rods "attract" lightning, or "repel" it.  This article says that generally metal objects are too small to "attract" lightning.  The same would apply to lightning rods...however a different source suggests they DO have a small "attracting" effect comparable to the height of the rod (even though that is not much).  Benjamin Franklin himself theorized a 45 degree cone of protection that occurs precisely because of this attracting effect; that 45 degree cone has been debunked but there is some region of influence similar to that.

In certain cases (such as big data centers) it may be more useful to "repel" lightning than try to attract and divert it.  And there are a variety of crazy looking and sometimes patented measures to do this and an engineering firm which specializes in it...but this is way out of the mainstream.

Many tall radio transmitting towers do attract lightning...and lighting strikes on such facilities happen often and the ones with well designed old fashioned diversion measures generally survive without major problems.

Actual lightning rods require VERY heavy wire such as 0 or 2 gauge, at least 3 ground rods, and ground bonding.  There is no "good" reason (except not insignificant cost!) why houses such not have such things.  But obviously taller and bigger structures are more at risk, and more money may be available for protective measures as well.


Thursday, March 1, 2018

TV stations OTA

I plan to be eliminating my Satellite TV system very soon.  I don't use it enough to justify the now $150 per month cost.  Just like Cable TV, the price rises every year.  I recall when I started my full-in cost was much less than $90, including HBO and Showtime.  It seemed reasonable then, especially thinking I might occasionally watch Real Time with Bill Maher or the Untold History of the USA.  But I haven't watched much of anything in the past 5 years.

In fact, most months I've owned it, I'd never even turned it on.  TV doesn't really resonate with me anymore.  I mostly listen to music and browse the internet, not even watching online videos very much.

But I'm loath to give anything up.  Over the years (but not so much in the past 10) I've watched the PBS station quite a lot.  I would certainly never give that up.

When I started with Dish network, they only offered HD for local channels IF you used an OTA receiver.  That is no longer true, they also provide local channels in HD through the Satellite system now.  But I'd gotten used to the OTA receiver and demanded the OTA "option" when they forced me to upgrade about 5 years ago.

I created an antenna just for the PBS station.  It's a folded wire dipole, similar to what is commonly used for FM tuners (which I still love and use daily), except cut to the length required for the PBS TV station.  I calculated the exact length required as 29 inches, and it has always worked great tacked to the wall in my kitchen about 7 feet high.  Perfect reception at strength in the 90's with no dropouts.  Before when I used a rabbit ears on top of the CRT TV I did get occasional dropouts, so my folded wire antenna is better.

I only intended the antenna for the PBS station, but soon discovered it could pick up all the other local channels also.  But I watched the other channels so infrequently I didn't realize until this week that they have frequent dropouts.

The PBS transmitter is only 5 miles away, and on VHF channel 9, so my folded wire dipole works perfectly.  It turns out nearly all the other channels are UHF channels despite their old-timey visible channel assignments.

Self-described channel 12 also transmits on its original VHF frequency corresponding to channel 12.

But the other local TV channels are all UHF, despite the numbers they describe themselves as.  (OTA TV takes care of this through some magic you can read about elsewhere.)

Here are the real channel assignments:

"Channel 4" really transmits on UHF channel 48
"Channel 5" really transmits on UHF channel 39
"Channel 29" really transmits on UHF channel 30 (?)

So it's no wonder that my 29 inch wire doesn't pick up the  UHF channels very well.  It's also orientated in the wrong direction for them, which doesn't help.

Here is the FCC channel finder giving info on all the local channels, including the actual channel they broadcast on and the location of the transmitter.  It turns out most TV channels are transmitted from the south relative to where I live.  I had erroneously believed many of them were to the west, based on the locations of their studios.

***** Testing the Clearstream 2V

So, I put the Clearsteam 2V atop my china cabinet, the best perch in the kitchen.  The width of the VHF dipole means I must twist it to the southwest, whereas straight south would be the optimal angle for stations from my house.

The VHF reception is slightly worse than the twinlead dipole I've had attached to the wall in a perhaps somewhat more optimal location.  I'm mainly saying that because my favorite Channel 9 has dropped down into the 60's of signal strength, but somehow it still looks fine.  On my dipole I get middle 70's through low 80's.  Somehow my PBS station gets perfect reception with signal strength in the 60's, whereas commercial stations around me seem to need 70's or better to keep from having dropouts.

Meanwhile the other VHF channel Channel 12 gets higher numbers, now up to the middle 80's.  And it comes in fine, but it came in fine before.

The UHF channels I couldn't get now come in OK, mostly, but I'm still getting occasional dropouts on Channel 4 and very rare dropouts on Channel 5.

I'm thinking of removing the VHF part of the antenna...which is merely being combined with the UHF part through a built-in combiner...and then use my old dipole for VHF stations, and combine it through an external combiner with the UHF from the clearstream.  That would give me the ability to rotate the clearstream for better reception.  Rotating and perhaps raising the Clearstream might help with those UHF stations it has trouble with.  But for the absolute best reception, it might need to be moved to the center of the wall near where my VHF antenna is.

[Note: I'm doing these tests with my old Dish receiver with the optional OTA module.  This is DTV technology from about 2012.  It's possible the Tivo OTA from 2013 might be slightly better.  I'm seriously hoping it isn't worse.]

And, if I move the relatively bulky Clearstream to the center of the wall, it will be even more ugly in my kitchen.

If I'm going to attach UHF antenna to the wall, it would be much nicer for it to be flat, like my Channel Master flat antenna, or perhaps a simple loop UHF antenna, or a home made "pennyloop" antenna which is apparently the basic design of the Clearstream 2V.

Way back when I started with OTA digital TV in 2009 which was using my first Dish receiver which had OTA built-in as standard equipment, I did ultimately use separate UHF and VHF antennas, combined with a VHF/UHF combiner I still have.  (It is absolutely necessary to use the combiner, else the two antennas will interfere and possibly cancel each other out.  It is NOT a simple splitter being used "in reverse.")

At the time I had a little indoor yagi type UHF antenna.  I still have that, somewhere, and it might be better than the Clearstream 2V for UHF.


Here is some information on the simple single loop antennas, like the ones that used to come with every TV.  They give a formula for optimal loop diameter, with the instructions to set the loop for the weakest useable signal, and probably the rest will be OK.

The formula is

diameter = 4537 / (6*N+389)

My weakest signal is for "Channel 4" which is actually channel 48.  So my optimal loop diameter would be:

6.7 inches

For Channel 30, the optimal loop diameter is:

8 inches

Apparently 7.5 inches is the common size of loop antennas prepackaged with TV sets.  Some guy named Tandy figured out he could sell a piece of wire bent into this shape and further looped to make two screw terminals to attach to the 300 ohm UHF terminals on the back of TV sets (then).  Next thing, he got so rich he bought Radio Shack.

One thing I've seen different answers to is "which way the loop should be arranged."  Some say the loop should look at the station edgewise, because the loop responds to the electric field.  Wikipedia answers this question well.  There are large loops and small loops.  Large loops are self-resonant to the desired frequency (like the ones I just calculated) and have maximum response perpendicular to the plane of the loop.  Small loops are much smaller than would be required for self-resonance and require capacitor tuning, and have maximum response within the plane of the loop--going horizontal if the feedline is at top or bottom, and vertical if the feedline is to the sides.

What you actually get in many of these flat antennas is something like a square loop with bowties in the middle.  Bowties and other features can be added to optimize various aspects of the performance. However, a simple loop by itself has wide band performance enough for channels 14-69, according to some on this thread.

Here is a discussion of the losses associated with different cables, adapters, and double female "barrel" connectors.


Results:

As I expected, my Channelmaster "Flatenna" works best very close to my existing Channel 9 folded dipole on the north wall of the kitchen.  Apparently any antenna would have to be around there to work well.  Atop the china cabinet, where I had plopped the Clearstream 2V, is not a good location.

There are similar good locations to the right of the folded dipole.  But that is where I plan to add a pot rack in the future.

I got very good results combining the $20 Flatenna with my $2 modified folded dipole through a $10 "VHF/UHF" combiner.  I decided to go with that combination after figuring out how to securely attach the flatenna to the wall (the "self adhesive" bits included were not good for that, but they were potentially good putting some space between the wall and the antenna, as is required because the bottom piece where the coax is attached bulges out otherwise).  I secured the top of the antenna with double stick "carpet tape" which is very secure, and the bottom part with big blobs of Blu Tac which helped to provide the required distance matching the coax attachment bulge.  And then, the coax itself goes through 3 AV staples, each of which could potentially hold the antenna on the wall if everything else failed.

Fearing that I would not be able to attach the Channelmaster to the wall, I had also purchased the single loop Clearstream model, which I intended to attach using a nylon strip wrapped around the top of the loop and nailed to the wall.  (I trust nails far more than stickum.)   However, that would be much more ugly than what I have now, which I (anyway) think is OK.

With this combination of antennas the Dish OTA receiver module was able to pick up all the local stations I had been aware of and cared about.  There were occasional dropouts on "Channel 4" (actually transmitted on UHF channel 48) and even one occurred on "Channel 5" (UHF channel 39) though the strength on channel 5 was shown as 83-87 well beyond the point at which dropouts never occur on VHF channel 9.

When I switched over the the OTA receiver of my new TiVo Romio OTA, it was even better.  I got zero dropouts on every channel, even channels I had not previously dreamed of picking up, such as 17, 35, and 60 (!).

In retrospect, it was a good thing I did my antenna tuning using the less-sensitive Dish OTA receiver because that permitted me to optimize the antenna better than the TiVo apparently needs.  Also, the TiVO receiver doesn't show signal strength readouts as easily as the Dish OTA does.

After doing the antenna fine tuning, I cancelled my Dish service, now costing $150 per month.  Cancelling the service required me to figure out "the receiver number" (shown on one particular info screen prefaced with R0, on the back of the Dish box itself which required me to make an iPhone photo in order to read, and actually, conveniently, on the top of the Dish box).  I also had to re-figure the email address I had used to register, and my password, a process that took about 30 minutes.   After doing all that, I found out I could not cancel service on the website anyway.  I had to make a phone call and wait on hold for 20 minutes.  In order to do that, I first had to figure out how to use the speakerphone feature of my iPhone, because I couldn't bear to hold the phone to my ear listening to the Dish advertisements for that long.  Finally, once I got ahold of the Dish closing agent, I had to argue for another 15 minutes to actually get them to do the cancellation.  As has happened many times before, they want to know why you are cancelling (because it costs so much, of course) and then they try to get you to stay on by offering lower and lower (temporary) prices.

It's too easy to say I'll never get a service like that again.  I know (because they told me) that I've been a dish customer for 13 years, which, according to them, shows my "satisfaction" and "loyalty."  Really, it shows my stupidity and unwillingness to confront the devil and get the job done.  I've possibly spent around $15,000 on a service which has certainly not provided $15,000 of satisfaction.  I'd barely used it at all for most of those 13 years, knowing full well I could get my favorite channel OTA for free.

I felt pretty much the same way when I cancelled my first Cable TV service in 1992.    And yet, I signed up for cable again only two years later, and then cancelled that twice and got Dish.

Now I get about 60 channels (including subchannels) for "free forever" with a $499 investment in the receiver/recorder/menu hardware+software.

But, I'm strongly thinking about getting ad free Hulu for $11.99 per month.  THAT's cheap enough not to worry about, and it gives any-time access to as vast an amount of programming as is available through many cable subscriptions.  And their series Handmaiden's Tale.

I'm very happy so far in my first day's experience with TiVO.  But I didn't include TiVO in the title of this post because Channelmaster makes a similar OTA device, which Consumer Reports basically said was as good as the TiVO at lower cost.  Also many TiVO models are designed for cable or network and do not have OTA capability at all.

TiVO would be especially expensive if you buy the service separately, either by the month or lifetime.  I'm very lucky in getting the Romio OTA basically at closeout pricing with lifetime service included.  Romio is said to be "2013 technology" by some.  However my unit is stamped with a "January 2018" manufacturing date code on the back.

AntennaWeb shows that I may be able to receive 61 channels from 23 over-the-air stations.


Update: It is now clear that "Channel 4" (actually UHF #48) is still experiencing  intermittent pixelization.  About every 3 minutes today.  Perhaps it depends on weather.  I may wish to test the one-loop Clearstream antenna mounted closer to my VHF antenna to fix it.  I also have ordered new RG6 coax and a more expensive VHF/UHF combiner which might help.

But I also see from Antennaweb that Channel 4 is going to change it's frequency anyway next year.

It's looking like the TiVO will pixelize if there is a slight problem, but avoid dropping out.  In comparison, the Dish OTA receiver simply drops out, for a minimum of about 5 seconds, when a problem occurs.  I've never seen much pixelization with the Dish receiver.  The dropouts are FAR more annoying, and perhaps that is the point, to make you think that OTA is useless and you must use the Satellite service.

Meanwhile, I've determined that TiVO will not apparently let me add the LinkTV apps which are available for AppleTV and Roku.  It has about 30 built-in apps (including Hulu, HBO Now, and Youtube) and you have to make do with those (and others they might add in future).  However I have also determined that LinkTV has many many programs (more than I could ever watch...) on Youtube and I can watch them through the TiVo that way.  Also, I can watch DemocracyNow! segments on Youtube (but I haven't seen entire shows yet...perhaps if I "Subscribe" I will see them).


Monday, February 26, 2018

Laser Projectors and Planetariums

Here is a new inexpensive light show projector device I purchased for my living room Relax scene with the main lights turned off.  The light show is very colorful and nice.  My friend thinks it is great.  

I bought it as a replacement for the now very faded (the lava has turned nearly white from fading) and somewhat dysfunctional 25 year old lava lamp, which I decided isn't good enough anymore.  Lava lamps generally take awhile to warm up, but the worn-out lava in my old lamp takes a couple hours to get moving, and when it does finally get moving, the faded white and broken-into-bits lava isn't very cool looking.  I could still use the lava lamp base, however, to house a multicolor LED bulb.  I use the base of another worn-out lava lamp for the soft yellow light in the Kitchen.

One minor annoyance for me is that when I switch on the Relax scene from my Kitchen Insteon multi-switch panel, it can switch on the soft light in the Kitchen, but in the living room it takes an additional press-and-hold on the pushbutton of the light projector itself, which is on top of a bookcase.  Since I have an auto-turn-off feature in my Insteon program itself, I don't need the auto-turn-off of the light projector, I could just bypass the internal switch if I could find a way to do that.

Here's a home laser show projector that looks pretty interesting, from a company which sells laser projectors from very cheap to very expensive (this one is in the middle of their range, about the largest one could imagine in a small home).  This looked like my "dream" home laser show projector.  But I decided I should focus on getting a real video projector and screen for the living room before getting an extra frill of this cost.  In the past year, I've seen very nice video projectors at the houses of 3 of my friends.  Since I have a movie party every month, I'm way behind on getting my own video projector.

I was also inspired to get a home planetarium.  Home planetariums have had their ups and downs over the years.  This appears to be a down phase.

Here's a page devoted to a Planetarium Museum which has some very impressive planetariums used in museums and schools over the past century.

Here's a good discussion of the leading home planetariums that were available recently.  I'd love to have the Homestar Extra, but they are now collectible and collectors are asking around $1500 on ebay.  The #2 rated Uncle Milton Star Theater Pro is similarly unavailable, with collectors asking well above $200 for used units.  But I found I could buy the identical Nashica online for around $200 brand new from a seller in Asia.  Then since it is one of the 3 machines supported by Miller Engineering, I was able to buy their upgraded star discs.  I got one upgrading my star count from 10,000 to 1,200,000, I got another showing Aurora Borealis, and a 3rd showing the star constellations (which have always been nearly impossible for me to figure out...and one big reason why I wanted a decent planetarium since I was 3).  Though let me say I find "my" constellations...such as the Big Butterfly...more intuitive than the traditional ones (Orion the Hunter).

Update: I now have my Nashica planetarium projector with 3 discs from Miller Engineering.  ME is correct, the star discs that come with the Nashica are not realistic in the least.  Imagine bright stars all over the sky, that's what the Nashica looks like.  The ME discs are quite realistic, even with the low power of the Nashica light (which actually seems quite sufficient).

Now, however, I see a major fly in the ointment.  NONE of these disc-based projectors can paint anything close to a realistic sky for two big reasons:

1) They don't have the Moon and Planets!  This goes way back, home planetariums have basically never had the moon and planets.  To do the planets, you need either a complicated mechanism which positions each planet image individually, as in the classic and gigantic Zeiss "dumbbell" shaped planetariums in big theatres (like my first love, the Planetarium at Los Angeles Griffith Park, which my family should have taken me to monthly instead of 2 times), or you need computerized imaging, which is still difficult even for big million dollar planetarium projectors (the most expensive Zeiss now available combines "static" star imagery which is simply too detailed for any kind of video system with the dynamic objects like planets synthesized in synchronized video...an enormous amount of engineering went into making the two very different things synchronize).

Why do they call these things "Planetariums" if they don't actually show the planets???  (I've often wondered that.  I was first very disappointed in "planetarium software" when it first came out for that very reason.  I want to see which of the objects in the sky are the planets!  I want to see where the planets are!  I complained about this to a maker of early planetarium software and they brutally brushed me off as some kind of idiot.)

In the big Zeiss "dumbbell" projectors, the Sun, Moon, and Planets are projected by circular rotating parts in the middle of the dumbbell.  Each planet must move separately against a fixed background of stars.

2) They can't actually paint the sky at your latitude!  What you get, with all these projectors like the various "Homestar" models up to and including the vaunted and long discontinued Homestar Extra which scalpers are charging $1500 for on ebay, and the Nashica and similar units, is the view from either the north pole (with the "northern hemisphere"discs) or the south pole (with the "southern hemisphere" discs).  In this polar view, the stars simply circle round and round.

This is why the big dumbbell projectors have that shape.  One end of the dumbell projects the northern hemisphere stars, and the other end projects the southern hemisphere stars.  If one end is straight up, you get the view from the north or south pole, depending on which end is up.  To get other latitudes, the dumbbell is tilted at an angle, and the machinery combines stars from the northern and southern hemispheres, changing the combination of stars all night long as the dumbell spins around its horizontal center.  (I figure this "combination" also requires some very sophisticated electronics and mechanics as well, since it always has to cut out all the stars you don't see.)

There is, actually, a way to do this on the cheap.  And that is to have a big ball (or similar shape).  You don't actually need a dumbell shape (which also allows for projecting the planets, moon, and sun, but as long as you are not going to do those anyway, you can just have a ball shape).  You can simply tilt the ball to the correct orientation for any particular latitude, and spin the ball around the resulting tilted axis to show what stars you are going to see that night.

This is actually the principle used in the very earliest home planetarium, the Spitz Jr.  Spitz had gotten started making intermediate size projectors for schools and smaller theaters based on the same principle, but instead of a cheaply mass produced (with considerable ingenuity) plastic ball with pin point holes in it, they used a bigger polygonal shape with actual glass lenses for stars and groups of stars--but that is going to be a lot more expensive than a ball with pin-point holes in it, but produce a far more realistic image, and while it may be much less expensive that the top Zeiss models, it's still going to be far more expensive than a plastic ball.

The whole raft of more recent home planetariums have mostly given up on that principle for using circular slides with single lenses which can, in principle, and with the Miller Engineering discs, project a somewhat realistic looking sky full of stars, but with the obvious limitation that it's only at the north or south pole, and if it moves it just goes round and round the center.  Boring!  I mean the motion part is boring, it is still interesting to see all the stars in their natural arrangement.

Now, there is one home planetarium projector based on a similar principle as the Spitz Jr, but using printed imagery on the surface of the ball.  It has this feature: you can set the latitude!  And, you can see the stars process over the nighttime from that latitude.  This is the iOptron.  People complain about many aspects of this home planetarium, including the realism, but it's cheap, and I've ordered one, and will report.

The ultimate "home" planetarium projector, if it had ever been made, would have been the Nova 100.  It had the rotating star ball AND two planets, which could be assigned.  It was never put into production.  The intended price was $600.  It was actually intended for elementary school classrooms.  It was designed by Harmonic Reed, who had gotten started manufacturing planetarium projectors with the Spitz Jr for Spitz.  The Spitz company itself moved upmarket to bigger and better projectors than the small institution A series that made it successful to such giants as the STP and STS, which challenged the Zeiss projectors that had originally inspired the company founder to make low cost units.  These were the glory days of the Space Race, when science funding nationwide got an extra federal boost, and when things like the Arpanet (predecessor of the Internet) got started.

Harmonic Reed did however actually make a very nice high school planetarium projector, the Nova III, which sold for $2000 (about $20,000 today).  It's suitable for a 14 foot dome...could it work in my living room???