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#1
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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 |
#2
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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 |
#3
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USB cords with DVD/RW
"Paul" wrote in message news 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 |
#4
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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 |
#5
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USB cords with DVD/RW
"Paul" wrote in message news 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 |
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