---------Original Messages:
> From: dm561 at torfree.net
> To: cctalk at classiccmp.org
> Date: Sun, 25 Nov 2007 06:44:14 -0500
> Subject: RE: FD400 drive troubleshooting
<snip>
>>>> Which just happens to be the ratio of 300RPM vs 360RPM, so that on a 300RPM
>>>> strobe disk w/a 60Hz light the 60Hz bars = 300RPM and the 50Hz bars = 360RPM.
>> Hi
>> I think you have the ratio backward. The 60 Hz disk for 360 RPM
>> can be used for the 50 Hz 300 RPM.
>> Dwight
<snip>
Hi
I guess my problem was reading your sentence. It just isn't clear
to me where you are saying they are equal and where they are not.
The part "60Hz bars = 300RPM and the 50Hz bars = 360RPM" seems
to be saying that "300RPM @ 60Hz = 360RPM @ 50Hz".
I'm sure I'm reading it wrong but it is still confusing. At least
we both agree on the basics and that is all that counts.
Dwight
--------Reply:
Well, I did say "the 60 and 50Hz *BARS*" (as in "stripe" or "band") at the same
frequency of illumination (60Hz), but perhaps I should have inserted "the speed
at which the bars seem to stop" instead of trying to keep it short and simple
(with exactly the opposite effect).
OK, how about this:
It just so happens that the ratio of 360RPM to 300RPM is the same as 60Hz to 50Hz.
Therefore, if you have a strobe disk for a 300RPM drive with both 50Hz and 60Hz bars
on it and a 60Hz source of illumination, then you can use the same disk to check the
speed of a 360RPM drive, since at 360RPM the 50Hz bars will appear to be stationary.
I'm talking about using a 300RPM disk at 60Hz (for the OP and others trying to check
the speed of a 360RPM FD400 or equivalent with 60Hz); you seem to be talking about
using a 360RPM strobe disk (if you found one) at 50Hz, a somewhat different situation
albeit one taking advantage of the same "coincidence".
But I think by now both our points have been made abundantly and painfully clear, and
I'm glad that we can finally put it to rest and not clutter up the archives further.
m
------------Original Message:
Date: Sun, 25 Nov 2007 09:59:52 -0800
From: dwight elvey <dkelvey at hotmail.com>
Subject: RE: FD400 drive troubleshooting
> BTW, you're wrong; it's 45.1127819548872180451127819548872
> ;-)
> m
>
Hi
My calculator didn't show any more digits but your results show
that the sequence repeats at 112781954887218045. If I could type
underline, one could underline that part and type ... This would
indicate a repeating sequence and be even more exactly correct ;)
Dwight
-----------Reply:
You're absolutely right!
Uncle!
m
Date: Sun, 25 Nov 2007 08:44:13 -0700
From: woodelf <bfranchuk at jetnet.ab.ca>
Subject: Re: Programming skills (was: Teaching kids about
computers...)
M H Stein wrote:
>> Why the "but"? Did I imply anything of the sort? Did I say that a
>> carpenter should know how to make an electric saw or even repair
>> it when it would be a more efficient use of his time and skills to just
>> take it to a shop or buy a new one?
>> ------
>But it does help if knows how to change the blade. :)
>Same with hardware/software -- know your tools.
I thought "being proficient in the use of the appropriate tools" kind of implied that...
But thanks for making it clear!
m
-------------- Original message from "Jay West" <jwest at classiccmp.org>: --------------
> At VCFX I was able to get the last major component for my TRS80 setup
> (already have the monitor, drives, and expansion interface). I got the
> keyboard unit for $20.
>
> Looks like all I'm missing is a real tandy power supply for the Model 1
> (yes, I know I can rig something up, but I'm looking for the real mccoy),
> and the buffered cable between keyboard and expansion interface.
>
> Anyone have one of those two items and is willing to trade?
>
> Jay West
>
>
Jay,
I offered you these last month ??? keyboard, PS . you would just have to take
the whole expansion unit. not just the cable.
never heard back ???
- jerry
One of our prize sponsors at VCF East was a company called Minds-On Toys (as a play of the phrase "hands-on") ... The owner, Tim Walker -- if I recall correctly -- went to MIT and studied all sorts of educational topics. He now sells the Digi-Comp replica. It is VERY easy to build and teaches kids about binary math.
> From: cclist at sydex.com
> To: cctalk at classiccmp.org
> Date: Sun, 25 Nov 2007 10:11:29 -0800
> Subject: RE: FD400 drive troubleshooting
>
> On 25 Nov 2007 at 9:50, dwight elvey wrote:
>
>> I was thinking about Tony's idea of the multiple and it occurred
>> to me that there was an issue. We've been thinking of the
>> flashes as instantaneous strobes while they have duration.
>
> Dwight, I think it's worse than that. There's also the idea of
> "persistance of vision" that gets in the way and also makes the
> strobe disc work--our eyes do not have instantaneous response and the
> only reason a strobe disc really works is because a fixed pattern is
> drilled into our optic nerves many times per second. Were this not
> the case, one could have a 45 RPM strobe disc, not with 400 bars, but
> with, say 4 or 50--but our eyes would likely not register these as a
> single continuous event.
>
> Of course I haven't tried this yet and I really should.
>
Hi
That is why I think the spiral with bars would work the
best. Persistance from adjacent bars would only be a
small issue at the tops and bottoms of the bars. The
eye would tend to follow the spiral.
Such spirals could be made for any RPM. In the case
of disk drives, one could make three different spirals.
Each for a percentage below and a percentage above
the exact one. This way, one could quickly see if the
speed were within a specific tolerance.
Dwight
_________________________________________________________________
Put your friends on the big screen with Windows Vista? + Windows Live?.
http://www.microsoft.com/windows/shop/specialoffers.mspx?ocid=TXT_TAGLM_CPC…
> From: cclist at sydex.com
>
> On 24 Nov 2007 at 22:27, dwight elvey wrote:
>
>> I got my math wrong. The fellow is also wrong.
>> 45/60 = .75.
>> 100/.75 = 133.333....
>> If rounded to 133, you get 45.11278195----
>> Still, using Tony's multiple method, 400 dots
>> would work fine. It would be a large disk but
>> it would work.
>
> 45 rpm is 0.75 r/sec. The strobe lamp flashes 100 times per second
> (50Hz * 2). So, the disc completes 3 complete revolutions in 4
> seconds. During those same 4 seconds, the lamp flashes 400 times.
>
> So there needs to be 400/3 bars on the disc if there is to be a bar
> exactly underneath the lamp for every flash, or 133.3333 bars, which
> causes the problem. If we increase the number of bars to 133
> exactly, the disk will be turning at 100/133 = 0.75188 r/sc or about
> 45.1128 rpm.
>
> If we put 400 bars on the disk, the lamp will flash once for every
> third bar passing under it. Not the crisp display we were hoping
> for, however--and I don't know what the visual error would be without
> trying it.
>
> At least that's how I compute it. So maybe the guy is right.
>
Hi Chuck
I was thinking about Tony's idea of the multiple and it occurred
to me that there was an issue. We've been thinking of the
flashes as instantaneous strobes while they have duration.
This would, as you state, cause a loss of contrast. This
would tend to overlap the dots and white space of adjacent
dots.
This would indicate that a continuous 400 dots would most likely
work poorly.
Still, the spiral method should work fine, with just as much
contrast as the single row method. One could use the original
size dots and spacing.
So, I feel that the fellow was incorrect that such a strobe disk
could not be made for exact 45 RPM.
Now, looking at the 78 RPM problem, the task seems more
difficult, for both 60Hz and worst for the 50Hz.
Still, three or four spirals with the correct spacing would be
enough, even if it didn't come out to a nice integer.
Dwight
_________________________________________________________________
Share life as it happens with the new Windows Live.Download today it's FREE!
http://www.windowslive.com/share.html?ocid=TXT_TAGLM_Wave2_sharelife_112007
---------Original Message:
Date: Sat, 24 Nov 2007 22:27:04 -0800
From: dwight elvey <dkelvey at hotmail.com>
Subject: RE: FD400 drive troubleshooting
> http://www.extremephono.com/free_turntable_strobe_disk.htm
>
> Note that the 50Hz disc is 45.11 RPM
>
> Cheers,
> Chuck
>
Hi
I got my math wrong. The fellow is also wrong.
45/60 = .75.
100/.75 = 133.333....
If rounded to 133, you get 45.11278195----
Still, using Tony's multiple method, 400 dots
would work fine. It would be a large disk but
it would work.
Dwight
-----------Reply:
If you're saying that he's wrong, that it's not 45.11 but should be
45.11278195 then I can see why you & I are arguing over whether
300/50 = 360/60 or 360/60 = 300/50...
BTW, you're wrong; it's 45.1127819548872180451127819548872
;-)
m
---------------Original Message:
Date: Sat, 24 Nov 2007 10:02:54 -0800
From: dwight elvey <dkelvey at hotmail.com>
Subject: RE: FD400 drive troubleshooting
>> From: dm561 at torfree.net
> ------------Original Messages:
>>> Date: Thu, 22 Nov 2007 12:17:31 -0800 (PST)
>>> From: Fred Cisin
>>> Subject: Re: FD400 drive troubleshooting
>>>
>>>>Many/most drives have 50Hz/60Hz zebra discs on the flywheel, for using a
>>>>flickering fluorescent light.
>>>
>>> Which just happens to be the ratio of 300RPM vs 360RPM, so that on a 300RPM
>>> strobe disk w/a 60Hz light the 60Hz bars = 300RPM and the 50Hz bars = 360RPM.
>>>
>>> FWIW,
>>
>> Hi
>> I think you have the ratio backward. The 60 Hz disk for 360 RPM
>> can be used for the 50 Hz 300 RPM.
>> Dwight
>>
>> ----------Reply:
>> Well, unless you're just saying that a 60Hz 360RPM strobe disk (if you had one)
>> would also sync at 300RPM under a 50Hz light, I don't see what's backward.
>Hi
> That is what I said. The disk with 20 bands would work for both
>a 360 RPM and 60Hz light or a 300 RPM and 50 Hz light.
--------
Gee, I thought that was what *I* said (and you claimed was backward).
Let's see; I said that 300RPM @ 50Hz = 360RPM @ 60Hz, and you
said that's backward - 360RPM @ 60Hz = 300RPM @ 50Hz.
Sounds like the same thing to me (and Tony) except that a 360RPM
strobe disk is a lot harder to find than a 300RPM.
Sheesh...
---------
> Tony mentioned that one could increase the number of bands for the
>problem of the 50Hz with a 360 RPM drive. It makes sense.
--------
Indeed; glad to hear it.
-------
> Tony mentioned that most 8 inch drives were speed controlled by
>the mains and as long as the belt was in good shape, using a strobe
>wasn't much needed.
-----
You really should read more carefully; he didn't say "most," he said
"all of mine," referring to his particular collection. In fact, many 8" drives
were 24VDC powered, including the Pertec FD400 which prompted
me to send (and regret) the original post that started this bizarre exchange...
m
I'll send you a private message with contact info for Doron Swade. He will know the answers to your questions.
-----Original Message-----
From: "B. Degnan" <billdeg at degnanco.com>
Subj: Babbage Calculating Machine Article 1833
Date: Sun Nov 25, 2007 9:44 am
Size: 2K
To: cctalk at classiccmp.org
New York Weekly Messenger 2-13-1833
Babbage Calculating Machine Article 1833
On the back page of this newspaper is an article that describes in some
detail the eye-witness account of a *working* machine: "...the greater part
of the calculating machine is already constructed....I have had the
advantage of seeing it actually calculate, and of studying its construction
with Mr. Babbage himself..."
Does this account describe a working computer? To help make this
determination I would want to learn more about the error checking
capability of this machine, which I assume was used for calculation of
significant digits. A described, Babbage's calculating machine could be
described as "computer-like" at least. I believe that this article reports
the closest Babbage got to a actual working computer. Or just an elaborate
calculator. There are no references in the article to what we today would
identify as punch cards or programming.
Download the PDF
http://www.vintagecomputer.net/babbage/charles_babbage_2-13-1833.pdf
...and read for yourself. The article describes error checking and how
results are viewed and how log tables could be calculated accurately, for
use in astronomy. The article noted that regarding the printer "..less
progress was made...".
In the 1830's news from Europe would take a few weeks to reach New York, as
boat was the only cross-Atlantic communications. Most articles in the paper
refer to end of December 1832 events, including the account of the
Calculating Machine.
Overall there was a lack of contemporary articles about Babbage's
calculating machine in 1832-35. I was able to find just the one often
quoted article by D Lardner: "Babbage's Calculating Engines" from
the Edinburgh Review 59 (1834) pg 263-327. The New York Weekly Messenger
article above was printed a year prior, making it among the first known
articles about Babbage's calculating machine. The apparent lack favorable
press and the loss of funding in 1834 obscured the fact that the machine
had a working visual "display" and was probably more complete than people
realize. Was the calculating machine programmable? Maybe. Most writings
about the Babbage projects were published a generation after the project
was cancelled and I don't think that it's possible to discount the notion
entirely.
