hi,
Some years ago, in order to qualify for my Inshore Yacht Masters ticket I had to learn Morse, what a pain.

E

 

hi,
Some years ago, in order to qualify for my Inshore Yacht Masters ticket I had to learn Morse, what a pain.

E

For boating purposes, back when they used 2.128 mHz for ship to ship and yacht to yacht communications it may have made some sense. I don't know if they still use that frequency anywhere, but it used to be quite busy and entertaining to listen to the tow-boats on the industrial canal an Mississippi river around New Orleans. I never heard Morse Code, but possibly a few of them could use it. They were using AM,and obviously with enough power to be clearly heard where I lived, about 15 miles from the navigable waters, back in 1965. So at one time knowing the code made sense, the arguments for the advantages of code are still valid, BUT not the reasons for demanding that every person know it.

 

As I think about the title of this thread, it is not about the demise of the persons, it is about the demise of the quantity of persons. Quite a difference, really. And I am thinking that I lost contact with a British Ham names Geoff, who I was supposed to provide with an IC chip, back in the late 1980's. He worked at Austin Rover in the city of Birmingham and he was an associate of Tom Richards. If he is reading this he should send me a message. I have not forgotten, just lost the contact information that was in a briefcase that was stolen from me.

 

Everyone wants to be fat, rich and do nothing!

 

Math, penmanship and memorization go to together. You don't have time to derive expressions in an exam, Derivatives of SIN and COS, you have to REMEMBER. I'd often confuse X's and Y's just because of how I wrote them. I ow have a much easier way to "collect terms". No one taught me. I just collect coefficients e.g. (1+2-3+2)x doing the multiplying in my head of small expressions.

One guy (graduate student) solved an interesting problem which I don't have the solution now. It's basically the VCR tape problem.
Converting "turns" of the take-up real to linear movement. Initial diameter is known and thickness is known. A turns-counter is fitted to the take-up reel.

When starting the process, initial turns are known, thus initial diameter is known.

I had to move a transparent Teflon cover (about 5" of film) over a quartz window periodically with a synchonous motor. It did not have to be accurate.

Integration and s=rθ comes into play. So does thickness of the film and the initial diameter of the mandral. So, if you started with a 1/4" mandrel, that's 0 turns on the mechanical indicator.

The film was thrown out when the process was complete. The film prevented deposition on the window. The window let in UV light.
The system renewed the window about every 2.5 minutes.

The math determines how many turns you have to move the mandrel to expose say 5" of linear film.

Then you have to convert to how long you have to run the synchronous motor to expose that amount of film.

You have initial conditions. The "tape counter" is a turns counter.

Your computation and movement has to match the turns counter.

It's a cool problem.

Measuring a board in half without doing "math" using convienient numbers. The triangle trick.

Marking a board. Use arrows, not lines. They are more precise. e.g. ∧ ∨


The thickness may have been 0.005" with some slop there too.

Hello there,

Oh that's interesting that you brought up the VCR tape counter problem. I had to solve that back in the late 1980's because it bothered me that when you plug a VCR tape in, you cant tell where you are on the tape thru the machine itself (although you could look in the plastic window on the cartridge to get a rough idea). I wanted decent accuracy so i looked into the problem of a tape winding onto a spindle and how the number of rotations related to the length of the tape and thus how the tape counter related to the position of the tape in time units.

What i found was that it was close to a spiral, it was a spiral, and there were various approximations but the actual spiral was not that difficult to work with anyway. What i found from that was that using calculus (basically derivatives really) i could tell from the counts where the tape was once plugged in, after a couple seconds of run and how the count changed over that time. The accuracy was pretty good too, but because the tape thickness can vary for different brand tapes, i had to know the thickness of the tape for each brand.
I was a lot of fun really working out the formula and seeing how well it worked with various tapes.
But then a wrench in the works. The next VCR tape deck i got had TIME on the counter, not a count of revolutions of the take up reel. That basically sucked, because now they were recording the TIME information on the tape along with the program information (picture, sound). That sounds all well and good, but i found that as the tape became used and recorded several times, the TIME information got corrupted and now there was no way to know where the tape position was exactly. WIthout the count and without the only method they used (TIME) it was a big letdown, and of course the fun of calculating where it was each time went to the dogs long before that.

The spiral is not that hard to figure out, and the rate of change is not that hard to calculate, so the position of the tape is not that hard to calculate. It takes a second or two though because you need two counts over a known period of time to be able ot use the derivative to calculate the tape position. I think i still have this in my notes i'll see if i can dig it up.

I found the formula i had found for the arc length of the spiral:
s=(1/2)*a*(TH*sqrt(1+TH^2)+ln(TH+sqrt(1+TH^2)))

'TH' is theta, 'a' is tape thickness (maybe divided by 2pi).

Somewhat interesting is the fact that different VCR's have different ratios between the counter count and the actual number of turns of the take up reel. I found with two different VCR's i had one that was '3' and the other was '4'.

There are also some irregularities that pop up such as when there are very few turns on the reel. The formula changes slightly because of the irregular way the tape lays on top of the previous layers due to the incline being abrupt with the first turn having a steep end that the second layer has to climb in order to lay on the top. There is even a tendency to overshoot the first layer because of the slight tendency to resist bending meaning it cant proceed in an upward direction and then abruptly arc back down to lay perfectly on top of the very end of the first layer. It gets very interesting.
Of course tape stretch is also an issue.

 

Maybe you could write it up as a project?

it gets really interesting when you add the "motor variable". We had two research systems at the time. I dedicated an entire PDP-11 to run both motor controls. program was written in Fortran. Native, basically to RT11.

Later, it was added to a PC running some sort of automation software, but the motor run time had to be done in hardware. it was some sort of Keithley/Metrabyte counter/timer board.

The good part was it did not have to be super-accurate. it just had to guarantee enough PTFE was moved approximately every 2.5 minutes or so.

In this system, I did anticipate using tension control, but it was unnecessary. I DID LEARN, that at low tensions or being able to achieve zero tension, you would have to apply a "negative" current to the magnetic clutch to remove residual magnetism. The controller wasn;t used and I did not account for residual magnetism.

This was in a vacuum system. The reactor was made from say a 4"h x 12"dia nearly solid piece of Stainless Steel. The Fedex guy got a real surprise when he said he could lift such a small package. It was between UPS limit of 50 lbs and Fed ex's limit of 70 lbs in a relatively small box.

 

Everyone wants to be fat, rich and do nothing!

NO! NO!! NO!!! I do NOT want to be fat, I want to be trim and fit so that I can do those things that I enjoy, and do the things that benefit others. Nor do I wish to be rich, except to have enough to do good. I would leave the doing nothing to those who are deceased. There is plenty of time to do nothing after one is dead.

 

It's an unfortunate result of our technology and socially involved government. People don't have a basic over-all knowledge or over-all skills of the past generations. In today's society......even the unskilled.....do not require an over-all, skill-knowledge. We have safety nets. If no jobs are available for your skill......the government will support you. Liberal grace.

We used to have high schools for that.

Think about what would happen if we lost electricity. And think what would happen if a third world country lost electricity.


What would happen if a large city in India lost power for one week. Life would go on. Much work and everyone eating would continue. You will not see roving gangs. Or the army.

Now....what would happen if a large city in the states lost power for one week? Much death and destruction. The disorder will kill you.....not the lack of electricity. Too many people in the states have lost the ability to take care of themselves. An army of some sort will be needed. Probably a liberal army giving equal rights and hearings to the roving gangs.

Imagine Paris or London blacked out for a week......an army would be needed there too.

What about Toronto?

Here in the north eastern quadrant of the USA we lost all power when the grid collapsed one very hot summer day. It was either 2002 or 2003, I do not recall which year exactly. Their was indeed a lot of traffic problems, since all of the signals were not working. It was indeed quite disorganized for several hours. And the power stayed off for most of a week. The disorder was indeed inconvenient, and some businesses did close, but we were never hungry, and never in a panic. There were no gang activities in our area because nobody would tolerate them. A gang of punks is no match for a couple with shotguns and lots of shells. It was a big inconvenience though, but not any sort of disaster.

 

North-East Blackout August 14 2003.

I was camping out in the woods. Didn't notice a thing.

 

I have been a HAM ("limited" license) for 46 years and am really pleased I don't have to learn Morse Code now. I tried to but was not able to get my mind around it.
Now I don't need to

I had no choice, being inducted into the Royal Corp of Signals, .

But I understood you could communicate using this method where voice contact was often impossible.
The U.S. Coast Guard still use Morse via lamp signalling, AFAIK.
Max.

 

My Dear Wife had no trouble learning Morse code but she is very musical and I think that helps a lot.
There are still some folks interested on building electronics as is evidenced by the electronics parts shops still open, like Jaycar. But we did have Tandy (Radio Shack) and Dick Smith too but they are gone. A lot of electronics is now purchased on line at greatly reduced prices as compared to years ago. It is incredible how cheap parts are now. It really is a great time to play electronics as there is now such a wide range of tracks to pursue, and the stuff that is able to be done now would have been impossible not that long ago. I try to encourage young ones to have a go, as I do with 3D printing in particular, by giving away 3D printer toys and info. Most people do not have a clue about 3D printing, and I think the same applies to electronics. Most folk have never thought of building something electronic themselves. That is why I love the Arduinos. They work very well as a "seed" to fan the interest going. It is so easy to get something working and to see the response to their first project working is wonderful.

 

Everyone wants to be fat, rich and do nothing!

Only one of those desires here

 

Only one of those desires here

I put in seven hours of work today. And the project looks good.

 

Maybe you could write it up as a project?

it gets really interesting when you add the "motor variable". We had two research systems at the time. I dedicated an entire PDP-11 to run both motor controls. program was written in Fortran. Native, basically to RT11.

Later, it was added to a PC running some sort of automation software, but the motor run time had to be done in hardware. it was some sort of Keithley/Metrabyte counter/timer board.

The good part was it did not have to be super-accurate. it just had to guarantee enough PTFE was moved approximately every 2.5 minutes or so.

In this system, I did anticipate using tension control, but it was unnecessary. I DID LEARN, that at low tensions or being able to achieve zero tension, you would have to apply a "negative" current to the magnetic clutch to remove residual magnetism. The controller wasn;t used and I did not account for residual magnetism.

This was in a vacuum system. The reactor was made from say a 4"h x 12"dia nearly solid piece of Stainless Steel. The Fedex guy got a real surprise when he said he could lift such a small package. It was between UPS limit of 50 lbs and Fed ex's limit of 70 lbs in a relatively small box.

Hi,

You think there would still be any use for it as now the VCR's are becoming extinct?
I havent even used my VCR in several years now, and that is the one with the TIME indicator rather than the COUNT of revolutions counter ... too bad.
Maybe there is some other equipment around that could use this kind of calculation?

 

The first time I saw the problem, I thought it was unique and it makes the problem solver think. In other words, it's an Engineering problem solved by math and complex enough that you can't "find" the solution.

Another problem, which I did have a book with he solution in it. I no longer have the book. Light choppers turn signals into a trapezoid, not a square wave. You need to be able to find the fudge factor with a DSP lock-in that measures the nth Fourier coefficient. So, you need the FF (Fudge factor) * Fourier coefficient measured to get the 0 to Peak value. You can measure the nth Fourier Coefficient with a DSP Lock-in.

For a sine wave Lock-in fed by trapezoid, all bets are off.

 

Hi,

You think there would still be any use for it as now the VCR's are becoming extinct?
I havent even used my VCR in several years now, and that is the one with the TIME indicator rather than the COUNT of revolutions counter ... too bad.
Maybe there is some other equipment around that could use this kind of calculation?

The way to count tape motion on a tape deck and have the units stay the same size is to not use the supply or take-up reels as the source. But that would not work for those that unload the tape path for rewind or fast forward.
BUT for those who would always use the T-120 size tape cartridges it would be simple to just monitor a hub, because if you always zero the counter when loading a rewound tape, every spot will be close to the same count even if the counts length changes from start to finish. Consistency pays off where accuracy is not available. Cheap, easy, and good enough for consumer use. That is how the counters on consumer tape machines always worked. With a belt driven counter that was the only option.

 

The first time I saw the problem, I thought it was unique and it makes the problem solver think. In other words, it's an Engineering problem solved by math and complex enough that you can't "find" the solution.

Another problem, which I did have a book with he solution in it. I no longer have the book. Light choppers turn signals into a trapezoid, not a square wave. You need to be able to find the fudge factor with a DSP lock-in that measures the nth Fourier coefficient. So, you need the FF (Fudge factor) * Fourier coefficient measured to get the 0 to Peak value. You can measure the nth Fourier Coefficient with a DSP Lock-in.

For a sine wave Lock-in fed by trapezoid, all bets are off.

Hi,

Yeah i found the problem interesting too and so went after it, and also i was able to deal with the tapes bettter which i used all the time back then.
The most interesting part turned up when i found that since the length always changes, the differential count changes, and thus looking at the differential count (which is all that we have when we have a tape counter that counts take up reel revs) tells me where we are on the tape length wise and that can be related to where we are on the tape time wise.
I'll see what i can dig up.

 

The way to count tape motion on a tape deck and have the units stay the same size is to not use the supply or take-up reels as the source. But that would not work for those that unload the tape path for rewind or fast forward.
BUT for those who would always use the T-120 size tape cartridges it would be simple to just monitor a hub, because if you always zero the counter when loading a rewound tape, every spot will be close to the same count even if the counts length changes from start to finish. Consistency pays off where accuracy is not available. Cheap, easy, and good enough for consumer use. That is how the counters on consumer tape machines always worked. With a belt driven counter that was the only option.

Hi,

Well the problem i faced was the tape counter monitored the take up reel so i had no choice unless i wanted to install my own sensor, which i really didnt want to be bothered with at the time.
Also, the hub counter, as you noted, will not allow a differential count that will show the place we are on the tape even after some run time because there's a zero derivative or constant derivative everywhere.
With the Archimedes spiral, the derivative changes everywhere so by knowing what the derivative is, we can immediately calculate the tepe position, and in practice knowing two tape counts and two times (say t=0 and t=2 seconds) we can estimate the derivative and thus estimate the position where the head is on the tape 2 seconds after the tape is plugged in, even though we have no idea where it is before we plug it in.
That's what i found intriguing once i got into the calculations.

If anyone here still has a VCR with take up reel counter they can try it as i'll post the results soon.
I got really good results when i did it. You do have to find the constants for your tape deck though.
Seems to me the old audio cassette players used to have this kind of counter too.

 

Once again, the simple work-aroud was to always set the counter to zero with all of the tape on the supply reel, and then recognize that the distance per count was changing, and that the exact location was also dependent on how tightly the tape was wound. And the tightness of winding depends on how much fast forward and rewind had been done in a specific session.

 

Once again, the simple work-aroud was to always set the counter to zero with all of the tape on the supply reel, and then recognize that the distance per count was changing, and that the exact location was also dependent on how tightly the tape was wound. And the tightness of winding depends on how much fast forward and rewind had been done in a specific session.

Hi,

Oh yes, but i never liked to have to rewind the tape just to find out where i was on that tape

The tightness made it vary a little, but still very practical.
I will show how simple this method is/was very soon so you will have more to go on.