LED Dim brighten depending on rotational speed...

[prozcrito]

Hello all,
I was wondering what i need to do this:

My goal is to mod a DVD drive with a clear cover so you can see the DVD/CD spinning. When no cd is in it or when there is no drive activity the LED will be off. When the cd/DVD is spinning the LED(s) will get brighter and dimmer based on the rotation of the disc.

Thanks

[Chewy_Solo]

i have really no idea myself, but im guessing that you could do some sort of sensor that detects the speed then it can change brightness based off of that? no idea rly :P hope i helped

[jdbnsn]

You can use the search function for some of these question, won't always help but if there has already been a solution it will save you the time of having to wait for replies. Below is a link to a worklog showing how to cut a drive open and make the disc visible. You may find that your desire to have an LED indicate disc RPM may be an advanced operation. I personally have no clue how you would manage it and unless you are highly skilled with electronics and soldering I wouldn't attempt it. Good luck on the mod though and welcome to TBCS!

http://www.thebestcasescenario.com/forum/showthread.php?t=7538&highlight=drive

[calumc]

It wont be exactly what you want but I have a window in my dvd drive and I just have the activity LED moved to the top of the drive and replaced with a blue one.
Its simple but is pretty close to what youre looking for.

[jdbnsn]

I think that is an excellent alternative.

[prozcrito]

I agree it is simpler but i'm trying to enter my case in modding contests so i have to be originial. Unfortunately my knowledge with electronics is limited. I was thinking to somehow use the concept of the the wind up flashlight you find at the Discovery store or at The Sharper Image but instead of the flashlight holding the charge, the charge depletes as soon as you stop spinning or it gets dimmer the slower you crank it.

Thanks very much for the input so far :D

[Tabspace]

you're probably better off going for the sound activated led for this project. your dvd probably spins up so quickly that all you'd get is a couple of seconds of dull to bright. no fun there. But lighting up to the rythm of your chaingun while you kick butt in unreal III?Awesome!!
you cant use your indicator light as a clock anyway because its on or off. no real easy way of doing this. you'd probably have to set up some kind of IR detection circuit with a modified bottom plate that let IR through once every revolution(on the side so as to not be interfered with by the dvd.). with your hard drive light you might be able to get away with this though.But still not very fun.

[calumc]

Maybe if you added a capacitor into my idea it would give a better result?

[mtekk]

This should be possible, that said, I hope you are comfortable with doing some possibly heavy modification to your DVD drive, and are good at soldering or know someone who is. The ideal way to get a LED to adjust brightness compared to RPM of the drive is to siphon off some of the current sent to the motor. If the motor is not brushless (which I doubt is the case) then the voltage supplied to the motor will be proportional to the RPM, and then everything is really easy. In that case you should use an op-amp as a buffer/power regulator so that you don't actually starve the motor in driving the LED (no/very little current would be siphoned off). That only works for non-pulsing supplies, if the supply is pulsating (e.g. it is driven by "Digital Voltage Regulation") then you will want to add a filtering capacitor in so that you get more or less the average voltage rather than the instantaneous voltage (it probably would work with out it, though it may flicker a bit).

HOWEVER, most motors in a computer are brushless, there are several reasons for this which all revolve around durability and they produce less electrical noise. Brushless motors have three wires (typically, some have four) connecting to them. One is a sensing wire, this should have the RPM of the drive encoded in it's signal in some form. You could assemble a microcontroller (and accompanying logic circuitry) to pick up the signal and decode it to a reasonable analog signal to apply to your LED. This will be complicated, and you'll need to figure out the modulation of the RPM data being used by the drive motor. There may be a different way of doing this, but this is what I think would be the most obvious route to pursue.

When is the contest/when is your submission due? I think this is a very cool idea, and I'd try it myself (on some old drive that I have sitting around) and of course help you get it implemented, but I will not have time until spring semester is over (and at that time I'll have a left over microcontroller from one of my EE classes).

[Helix666]

In a CD drive, the motors are not brushless.
(Just thought I'd let you know ;) )

[mtekk]

In a CD drive, the motors are not brushless.
(Just thought I'd let you know ;) )

Are you sure? I had a DVD drive that was apart and I could have sworn it had more than two wires going to it (a good indication that it could be brushless). I'll check on this later today. That fact that old CD/DVD drives with working motors are routinely taken apart to grab their brushless motors in model aircraft would lead me to assume that there is a good chance it is a brushless motor.

[xmastree]

I always thought that the spinning motor was brushless and the head movement motor was a stepper.

[mtekk]

That's more or less what I've seen. The motor driving the disk(s) is usually brushless, the "seeking" ones (move the reading head) are typically brushed motors (for removable disks, hard drives have their own coil/magnet thing).

[Helix666]

Well, in all the ones I've dismantled, both the motor driving the disc and the one moving the laser have brushes.
Although I can check a slightly more modern one. bear with me.

EDIT: hm, seems I was wrong. The newer CD drives do have stepper motors.