Using a real Harddrive
as an IDE activity indicator
A Mod from:
ZapWizard
I wanted a Harddrive window on my PC, but with no way to show it off I came up with this mod.
The moving head effect is very cool to look at, and provides a unique aspect to any case.
So I decided that if I mounted a laptop harddrive to the front of my case, and wired it so that when the IDE activity LED was active the head would move.
So... I got a cheap laptop harddrive and went to work.
First, I will show you how I did it with my drive (A rare find), then at the end explain how you can modify a normal drive to do the same.
The hardrive: 130Mb laptop hardrive, $5 at Goodwill computers. Works perfectly (For now)
It is slightly shorter than a normal laptop drive.
The one on the left is my first attempt at this mod, I broke some wires on this drive though
My guide to putting a window on it is here: Laptop Harddrive window
TAKE IT APART!!!
This took a normal screwdriver, and a star driver. The HD is in a separate case from the electronics.
The drive casing is VERY thin, good in case I want to separate it from the electronics
The cable to the motor, I though I would end up having to wire to this but as I will explain later I didn't have to hack straight to the motor.
Now for some hardware hacking!
I connected a 1Kohm resistor to +5 volts and started poking around the drive until the head moved.
I repeated with the 1K connected to ground. I found two points that worked. (Keep reading)
These pins saved me TONS of time
The back of the drive has TONS of testing points, some even labeled!
I found a group of four points right near each other, 5 Volts, Ground,
And two points that are wired directly to the head's coil controller chip.
The first pin sets the reference voltage of the comparator.
The second sets the trip voltage, if it is higher than the reference the head moves to one side, if it is lower than the head moves the other way, PERFECT!!! (Your results may vary)
I soldered a 4 wire cable to the points, and started experimenting.
In the end I connected a 1k ohm resistor from +5volt to Reference.
The trip wire was connected to Pin 39 on my Kazaa Hardrive, in series with a 33uF capacitor and 100 ohm resistor.
The Other two wires powered the drive.
I ran into one problem: The head moves TOO fast.
When there is a lot of activity such as scandisk or defragmenting the head violently moves back and forth making tons of noise when it hits the side bumpers.
So I decided to look up the controller chips to get their spec sheets and see what I could do to slow it down.
(I should have done this in the first place it would have saved lots of time)
On the board it has two motor controller IC's. The one on the left controls the Motor for the disk. The one on the right controls the head movement. I searched Google for their part numbers (Plus PDF) to find their spec sheets.
They are located here: MOTOR IC - HEAD IC
-Hacking the Head IC-
The IC is and Allegro Microsystems A8932CLWA
Pin 16 is reference voltage for the head movement comparator.
Pin 15 is the active or trip voltage for the movement comparator.
These two were wire directly to the test points I soldered to, but I need to slow the head's movement down.
So I connected a 33uF capacitor between pin 16 and pin 19 (Which is wired to the output of the comparator)
This way when the comparator is tripped the capacitor charges up, raising the voltage level at the reference.
This causes the head to move slower, until the max voltage is reached. Perfect!
Unfortunately the drive turns this IC off after a few seconds due to the fact that the drive is now hacked and the data is corrupt. Well, Pin 18 is Power off (Active low).
So I disconnected the pin from the board and wired a 1kohm resistor from +5volts to pin18. This made sure that the IC can never be turned off.
-Hacking the Motor IC-
This IC is also turned off after the self diagnostic, so looking at the spec sheet there are several pins that can stop it from working.
Pin 21 is called CHIP SELECT, when it is low the microcontroller can program it to stop or go, so wiring this high stops all data from the microcontroller.
Pin 20 is Reset, when this is low the chip is in sleep mode, so again this is wired high.
Pin 11 is brake, this stops the motor cold, so again this is wired high.
Now when it is powered up the chip spins up the motor to a nominal speed and keeps it there, PERFECT!
Here are some animated GIF of the movement when totally done.
The actual disk was removed so that I didn't scratch it, I replaced it when I was done.
( My still camera only captures 5 FPS )
Small 214Kb (1/2 of frames removed)
Large 410Kb (5 Frames per second)
Original Harddrive (The one with the window)
In the end the result was perfect, it provided the random head movement, in sync with my harddrive's activity LED. Making it seem like it was the actual drive accessing data.
I don't have final picture yet as I am still deciding on where to place LED's.
-Recreating this modification-
To recreate this will take some skills and bravery,
The chips to control the motors are already there, USE THEM!
Look up the chip numbers of the IC's (Search Google for "Chip### +PDF)
Search until you find the chips that control the motor and head movement.
Use their spec sheets to adapt them to do what you need.
Or simply hack around, like I first did until you get some results.
Have fun!
I do not have any schematics as this mod was done by just plain fooling around.
This modification is HARD I cannot answer questions about specific drives, or design custom circuits.
I can help you with a specific IC, but only AFTER you have found the Spec sheet.
