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In article <212@ddsw1.UUCP> dino@ddsw1.UUCP (Laura Watson) writes:
>Does anyone here know anything about a way to add an 'autoreversing'
>mechanism to a cassette tape player that doesnt' have this feature already?
>Any advice or pointers to information would be appreciated.  

Unfortunately, most, if not all, forward-only playing cassette machines 
physically, mechanically and spiritually can never be retrofitted for 
autoreverse without major restructuring of the tape transport and electronics.

Here's why:

(1) In order to play the other side of a cassette after reaching the end of
one side, you have to have sensors to detect the tape has reached the end of 
a side - most forward-only decks don't have these sensors (unless, perhaps
the deck is 'auto-stop').

(2) Once the tape has played forwards, the transport must reverse and run at
play speed until the end of the other side - something forward-only decks are
generally incapable of doing.  There's not much one can do about this one 
unless the deck in question has a forward/reverse transport and the 
manufacturer is only letting you run is one direction.

(3) The deck's electronics would need an overhaul to accomodate a forward/
reverse playback (NOTE: and record and erase, if the machine records) head.
Cassettes have two tracks (mono) or four tracks (stereo), one half of which
are used for one side and the other track(s) for the opposite side. One
side's tracks run along half of the tape - when you flip the tape over, you
bring the other side's tracks to bear on the set of heads to playback, record
and erase (see note above). Only one half of the tape is dealt with at a time 
by the standard uni-directional recorder or player.  An autoreverse deck has a 
special set of heads that handle all of the tracks for both sides at once.  
When the tape reverses, the deck automatically switches the signals 
from the one side's portion of the heads to the other side's portion of the 
heads.


A Picture (that may or may not help) :

-----------------------------------------------------------------------------
=========================== Side 2's track(s), read with the tape going <----
=========================== Side 1's track(s), read with the tape going ---->
-----------------------------------------------------------------------------
A slice of a cassette tape, normal forward tape direction ---->

A standard forward-only cassette playback (or record or erase) head :

---------
|       |
| ====  |  Note that the active area of the head can only read one side of
---------  the tape at a time - you have to flip the tape over to read the
		   other side.

An autoreverse cassette playback (or record or erase) head :

---------
| ====  |
| ====  |  Note that the active area of the head can read both sides of
---------  the tape at a time - however, in order to read side 2 going the
		   right direction, the tape has to be going in reverse from the
           normal side 1 direction.

I hope this explanation helped those who needed it and didn't bore to death 
those who could care less or already knew how their cassette machines work.


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