USB cords with DVD/RW
 

I have two cord with an external DVD/RW I bought some time back. There's
two cords the one I use with USB 2 on my tower to the DVD/RW and looks like
data but it's power too.

This second one IDK what it's for. I goes to the "power" interface on
the DVD/RW. I guess I don't need it. But idk what would. Is it to get your
DVD/RW to move faster or something?

Bill

USB cords with DVD/RW
 

Bill Cunningham wrote:
I have two cord with an external DVD/RW I bought some time back. There's
two cords the one I use with USB 2 on my tower to the DVD/RW and looks like
data but it's power too.

This second one IDK what it's for. I goes to the "power" interface on
the DVD/RW. I guess I don't need it. But idk what would. Is it to get your
DVD/RW to move faster or something?

Bill



Is it like this ?

A USB cable with two headers ?

VCC ---------+
X----- |
X----- |
GND ---+ |
__________| |
| |
| VCC ---------+---------- 5V 1A max
| D+ -------------------- USB2 data
| D- --------------------
| GND ---+---------------- GND
} |
+----------+

It's a way to extract more current flow
for the +5V VCC supply to the drive.

In that diagram, two 5V 500mA connectors work
together, to make a 5V 1000mA powering source. The
connectors should not go into the same USB stack,
and should be staggered on different stacks (to
avoid the Polyfuse opening).

*******

Some drives have a barrel connector for
powering with an external adapter. Which
is another way to do it. The external adapter
then provides the 5V the "slim" drive is using.

On full sized 5.25" drives, the adapter is 12V
or 12V/5V with four pins. And the adapter has
no trouble running those (only a BluRay might
be a bit much for your average hard drive adapter).
I don't think you're referring to one of those
older full height motorized tray ones.

*******

If the drive was "USB3", then the higher current
rating of the USB3 plug may mean just one
connector is needed.

The DVD drive spins at a controlled speed, so no,
it doesn't go faster if the voltage is increased
or anything. It's strictly regulated with a
three phase motor (with low torque ripple) and
the laser actually tracks a spiral path, like the
DVD was a long play vinyl recording.

The drive has three spinning states it can be in:

1) No data errors. The rotational speed cannot speed
up indefinitely. Presumably the media tag is used
to decide what a good max speed is. DVDs rotate slower
than CDs, in practical usage. Since good media is hard
to find, you might get up to around 7MB/sec or so.

2) Seeing too many errors. In this state, the motor may
be set to a lower rotational speed, in the belief that
this will give a better opportunity for data recovery.
Note that even without this, the three dimensional Reed
Soloman error recovery is very good, and uncorrected errors
hardly get through.

3) When the DVD really screws up, is when the laser cannot
track the groove. DVD+ and DVD- use a different encoding
for the groove. The laser uses that modulation (whatever it
is), to keep the laser head (which doesn't touch the disc),
right over top of the spiral path it has to follow. it
is the "loss of laser lock" which actually causes unreadable
media, and the motor running in fits and jerks. If the
laser could maintain lock as in (2), then Reed Solomon
does the rest.

HTH,
Paul

USB cords with DVD/RW
 

"Paul" wrote in message
...
Is it like this ?

A USB cable with two headers ?

VCC ---------+
X----- |
X----- |
GND ---+ |
__________| |
| |
| VCC ---------+---------- 5V 1A max
| D+ -------------------- USB2 data
| D- --------------------
| GND ---+---------------- GND
} |
+----------+

It's a way to extract more current flow
for the +5V VCC supply to the drive.

In that diagram, two 5V 500mA connectors work
together, to make a 5V 1000mA powering source. The
connectors should not go into the same USB stack,
and should be staggered on different stacks (to
avoid the Polyfuse opening).

*******

Some drives have a barrel connector for
powering with an external adapter. Which
is another way to do it. The external adapter
then provides the 5V the "slim" drive is using.

On full sized 5.25" drives, the adapter is 12V
or 12V/5V with four pins. And the adapter has
no trouble running those (only a BluRay might
be a bit much for your average hard drive adapter).
I don't think you're referring to one of those
older full height motorized tray ones.

*******

If the drive was "USB3", then the higher current
rating of the USB3 plug may mean just one
connector is needed.

The DVD drive spins at a controlled speed, so no,
it doesn't go faster if the voltage is increased
or anything. It's strictly regulated with a
three phase motor (with low torque ripple) and
the laser actually tracks a spiral path, like the
DVD was a long play vinyl recording.

The drive has three spinning states it can be in:

1) No data errors. The rotational speed cannot speed
up indefinitely. Presumably the media tag is used
to decide what a good max speed is. DVDs rotate slower
than CDs, in practical usage. Since good media is hard
to find, you might get up to around 7MB/sec or so.

2) Seeing too many errors. In this state, the motor may
be set to a lower rotational speed, in the belief that
this will give a better opportunity for data recovery.
Note that even without this, the three dimensional Reed
Soloman error recovery is very good, and uncorrected errors
hardly get through.

3) When the DVD really screws up, is when the laser cannot
track the groove. DVD+ and DVD- use a different encoding
for the groove. The laser uses that modulation (whatever it
is), to keep the laser head (which doesn't touch the disc),
right over top of the spiral path it has to follow. it
is the "loss of laser lock" which actually causes unreadable
media, and the motor running in fits and jerks. If the
laser could maintain lock as in (2), then Reed Solomon
does the rest.

HTH,
Paul

What would increased current flow do? The one USB plugged into the USB port
does provide all the voltage to run the DVD motor. 5 V

Bill

USB cords with DVD/RW
 

Bill Cunningham wrote:

What would increased current flow do? The one USB plugged into the USB port
does provide all the voltage to run the DVD motor. 5 V

Bill

What does the rating on the casing of the
DVD drive say ?

The USB port is rated at 5V @ 500mA for USB2.
USB3 is a bit higher.

They can cap the current flow to the motor,
but it affects spinup time. Once the spindle is
up to speed, only air friction losses have to
be made up, so the current flow to maintain speed
shouldn't be quite as high as the startup current.

Hard drives run in a kind of constant current
mode during spinup. But the value of the limit
set on those, varies in a counter-intuitive way.
Small drives draw large current, so they can
spin up fast (as boot drives). Large capacity
drives (with four platters) draw smaller current
flows during spinup, and take more time to get
up to speed. I believe there is a factor of
that nature in optical drives too, in that the
acceleration is controlled, and could be
controlled so it doesn't draw too much current.

The only "slim" optical drive I have here, is in my
laptop, and it wouldn't be that easy to get
a measurement off it.

So if something provided more current for the
optical drive, the drive doesn't have to use it.
It then remains as an "untapped resource".

If the drive drew too much current, then the fuse
could open and stop it from operating. That's why
they made those cables with two connectors on it.
So you could plug into two different stacks,
and draw current from two different fuses.

Paul

USB cords with DVD/RW
 

"Paul" wrote in message
...

What does the rating on the casing of the
DVD drive say ?
[...]

The casingsimply says fragile. And there is a reference to instructions. I
don't remember getting any instructions but they're long gone now. Maybe a
slip of paper. Once again thanks for your help Paul.

Bill