The Lemon Fool

This short video won't win any BAFTAs but it does show the light (in this case, an old-style filament lamp rather than an LED) and how the tape runs slowly through the machine while being scanned at a much higher speed by a pair of heads on a spinning drum.

https://www.youtube.com/watch?v=lApDKLDzOnI


Julian F. G. W.

jfgw wrote:

AleisterCrowley wrote:Looks like a right cockamamie scheme!

How would you do it?

...

Another reason that I can think of for having separate sensors for the start and end of the tape is that, without these, the clear leader would end up being passed over the head drum. I can imagine that this would cause increased wear or even potentially cause damage.


Julian F. G. W.

That does make sense to a point, although I'd be inclined to have the sensors either side of the read head with two LEDs rather than some crazy Heath Robinson/Rube Goldberg scheme poking a double sided LED in a hole and detecting lights out of other holes! I'm sure bits of dirt and misplaced labels cause issues

jfgw wrote:Another reason that I can think of for having separate sensors for the start and end of the tape is that, without these, the clear leader would end up being passed over the head drum. I can imagine that this would cause increased wear or even potentially cause damage.

I've just looked at some of my VHS tapes, including a couple of virgin ones and a couple that I'd used and rewound, and with the flap open I see that all of them have the clear leader across the whole of the front, head facing, with the join at the very right hand end (looking at it).

So, either the leader is passed over the drum head, or, if that's really to be avoided, the player winds on a fraction before pulling out the tape to the head, or the leader is just the right shortness so that by the action of the player pulling out the tape the leader can't be stretched out to actually touch the head. From the video you posted it looks like it's probably the latter.

I must admit I always thought end/start of tape detection was done by physical resistance, i.e. by not being able to wind any further, as all the VCRs I had on rewinding went whir-whir-whir-thud-pause-clunk, if you follow what I mean.

AleisterCrowley wrote:That does make sense to a point, although I'd be inclined to have the sensors either side of the read head with two LEDs rather than some crazy Heath Robinson/Rube Goldberg scheme poking a double sided LED in a hole and detecting lights out of other holes! I'm sure bits of dirt and misplaced labels cause issues

VHS was designed some years ago. LED dies where relatively expensive, plastic lenses less so. Part count affects cost. There were and are a lot of cockamamie schemes. My favorite is when somebody figured out to make RF band pass filter with 5 inductors instead of 6 and everybody* was studying hyperbolic equations for a few years.

* For a very limited definition of everybody.

God, that brings back some gruesome memories - filter design...Chebyshev, Butterworth....

AleisterCrowley wrote:end of tape detector???

Why would you need that? Surely cassette tapes had no use for any such thing, and by implication any later tape format had an obvious precedent. What did old reel-to-reel tapes do at the end?

Don't blame me, it wasn't my idea!

AleisterCrowley wrote:That does make sense to a point, although I'd be inclined to have the sensors either side of the read head with two LEDs rather than some crazy Heath Robinson/Rube Goldberg scheme poking a double sided LED in a hole and detecting lights out of other holes! I'm sure bits of dirt and misplaced labels cause issues

A problem with that is that the tape would have to be loaded (or, at least, partly loaded) for the end detection to work. VHS machines retract the tape into the cassette before doing a full-speed rewind or fast-forward. Also, with top-loaders, the photodiodes could also detect whether or not a tape had been inserted.

Another issue is that you need a light source one side of the tape and a detector (such as a photodiode) the other. With the light source poking inside the cassette, this is easy. If the tape had to be loaded first, then one half of the end-of-tape detector would have to be moved out of the way while loading and unloading and things would be even more complicated. (This could be why V2000 and Betamax used different methods.) Compare this with the capstan and pinch roller; the cassette drops down over the capstan so that the capstan is behind the tape and the pinch roller is in front. If it were not done this way, one or other would have to drop down while the tape was loaded.

Given where the holes are, misplaced labels would not be a problem. If there was so much dirt for it to cause a problem, I suspect that there would be other issues too.

mc2fool wrote:I must admit I always thought end/start of tape detection was done by physical resistance, i.e. by not being able to wind any further, as all the VCRs I had on rewinding went whir-whir-whir-thud-pause-clunk, if you follow what I mean.

I suspect that that would result in a lot of stretched, if not broken, tapes.

Julian F. G. W.

UncleEbenezer wrote:

AleisterCrowley wrote:end of tape detector???

Why would you need that? Surely cassette tapes had no use for any such thing, and by implication any later tape format had an obvious precedent. What did old reel-to-reel tapes do at the end?

I think I recall audio compact cassette mechanisms having a little plastic tab that went in one of the holes in the cassette. When the tape got tight, it would push the tab down and shut off the machine (or auto-reverse it).

I thought reel-to-reel just kept going with the loose end of the tape making a flick-flick-flick sound and with no tape going past the heads (not something you want to happen with a cassette). Some machines had auto-reverse where a short length of sensor tape had to be stuck onto the back of the leader.


Julian F. G. W.

UncleEbenezer wrote: Surely cassette tapes had no use for any such thing, and by implication any later tape format had an obvious precedent. What did old reel-to-reel tapes do at the end?

On reel-to-reel decks the end of the tape pulled out of the slot in the spool of the feed reel. The take up reel continued to spin and the loose end went whap-whap-whap against some part of the deck as tape tension fought with centrifugal force (or inertia if you insist on non-rotating frames of reference).

You had to refeed the tape to rewind. Even if you stopped before the end you still wanted to refeed before rewinding. Rewinding was best done with the tape not passing through the read/write heads. Movie projectors worked the same way.

I am wondering why I bothered with this one

Three more to go,



Not many guesses for no. 6 yet.

There have been some fairly specific suggestions for no. 9:
It is not for a roller blind;
It is not for a venetian blind;
It is not for a vertical blind.
I have already told you you are very close, so what is it for? Giving us these is not the only thing they did for us!

I have given some clues for no. 10:
The middle bit screws in;
Both ends of the grey bit look like a wall plug;
The screw head is not big enough to fix anything.


Julian F. G. W.

9 Roman Blinds...but, I have these in my lounge and there are no plastic bits -just hoops and nylon cords with a knob on the end (usually me...)

jfgw wrote:I am wondering why I bothered with this one

Ignore that. I had my second jab yesterday. I am not feeling 100% today.

jfgw wrote:
Not many guesses for no. 6 yet.

But I suspect there's loads of us really interested to find out what it turns out to be though Julian!

Cheers,

Itsallaguess

It just looks so like all the conference phones I've used I can't think beyond that answer

AleisterCrowley wrote:9 Roman Blinds...but, I have these in my lounge and there are no plastic bits -just hoops and nylon cords with a knob on the end (usually me...)

Correct answer AleisterCrowley. It is a roman blind sidewinder. https://www.jones-interiors.com/blind-cassette-systems/


Julian F. G. W.

AleisterCrowley wrote:It just looks so like all the conference phones I've used I can't think beyond that answer

Not audio-related.


Julian F. G. W.

No. 6 digital magnifier.

RC

ReformedCharacter wrote:No. 6 digital magnifier.

RC

Not a digital magnifier.

Well I'll be surprised if anyone guesses no 6 ... I didn't even know such a thing existed! Spoiler. (Yes, I cheated!)