softech@micomz.UUCP (06/08/83)
I was reading all the debate about CD players in cars, and it occured to me that we all forgot one VERY important thing: Playing a CD in a moving vehicle would be about as difficult as playing a standard record (with stylus and all). The tracking system in CD players is so precise and so fragile that it would be impossible to design one small enough and strong enough to resist the G-forces involved without losing the necessary precision. Remember that the little laser beam must be kept ON TRACK and IN FOCUS at all times. Now we are talking about tracks that are only 1/20 th of a normal record groove in width, and there is no mechanical contact to do the tracking with! Its all done optically by a complex servo mechanism that analyses the shape of the laser on the record surface. Minute fluctuations due to hole centering errors or warpage of the surface are corrected by ultra-fast voice-coils that hold the focusing apparatus (remember the little devil SPINS!). A small bump on the road would easily cause several seconds of "errors", if not complete jumping of tracks. So, for all of you waiting to trade-in your old Delco... (By the way, the same goes for the Walkies fans, unless you go real easy on your roller skates...) Richard "Ears" Blouin. !philabs!micomvax!micomz!softech
ksbszabo@wateng.UUCP (Kevin S. B. Szabo) (06/10/83)
I find it somewhat incomprehensible to still see people say something is impossible, especially someone who is obviously a little more technically oriented than the general public. I believe the comment that CD's are impossible due to the stylus tracking problem misses on one main point. It is precisely due to the fact that no contact with the playing surface is required that tracking is simplified. The mass of the "stylus" is no longer a factor when playing since the stylus is probably anchored with some form of leadscrew, instead of floating as is necessary with the mechanical pickup. Fine positioning of the actual pickup may still be done by magnetic means, the servo amplifiers would of course have to be accurate enough to compensate for the forces exerted on the small pickup. I do not consider the design of these amplifiers to be impossible either. Problems of wow and flutter can also be dealt with in the car environment. Since the information off the disk is already in a digital format it is not a difficult task to perform a delay line type operation on the data. This circuit can take take at a certain rate (with jitter, also known as wow and flutter) and output a stream of data at a constant rate. Remember that the digital information is sampled, and hence has a recoverable clock that allows regeneration of timing information. Standard records of course have no such information present. Note that challenging problems are met with new and interesting solutions. The problem of achieving the disk - head distances seen in present disk drives would be difficult to surmount without flying heads. I think this problem is of similar difficulty. Also note that I never said it would be a) cheap or b) easy. Zazzy
caf@cdi.UUCP (06/10/83)
The key phrase is ultra-fast servo system. I suspect that the acceleration encountered in these systems could easily hit a G or two. In that case, only a car wreck or sharp bottoming of the suspension would cause problems. -- Chuck Forsberg, Chief Engr, Computer Development Inc. 6700 S. W. 105th, Beaverton OR 97005 (503) 646-1599 cdi!caf
darrelj@sdcrdcf.UUCP (06/15/83)
Playing CD in a car is likened to playing a phonograph in a car in a recent comment here. It has been done. I have dim (~20 years ago) memories of record players in the dashboard. I haven't any recollection of having heard one, but presumably they (generally) tracked by a combination of high tracking force and spring isolation. I'm pretty sure it only played disks in the 8" format. This predates any reasonable tape alternatives (the 8-track was invented by Mr. Lear (also inventor of a small jet) specifically as a better mousetrap for car audio.
jeff@tesla.UUCP (06/17/83)
Chrysler did offer a record player for cars about 20 years ago. I wonder if they sold any. Jeff
/a3/c5215a/weheh/user@mhuxa.UUCP (06/18/83)
I once rode in a taxi in St. Thomas, Virgin Is. that had an in-dash record player. As I recall, it played 45's. R. Gordon mhuxa!weheh