How to Transform Old Hard Drive Into Time Gadget

...
Hello everyone!

So, what are we going to recycle today?
Let's take a look what we have in that big box. I'm pretty sure we'll find something to start with.
Well, that's hard drive... one more... two more... plenty more; internal, external, IDE, SCSI, MFM...
Wow, that's quite a load of junk. Sadly, overall capacity of this box of HDs is much less than capacity of one HD which is humming inside my desktop today.
Let's see what we can do for those guys... this one would be good as paperweight, this one as door stopper, but this external SCSI HD looks very promising.

Let's examine it closer:
- solid metal case;
- LED at front panel;
- power connector and switch at the back;
- power supply +5V, +!2V;
- 12V fan;

That's almost finished device, it just needs new guts.
By the way, I've always wanted my own hard drive clock, and right now I have everything to build one.
That's settled. We are making hard drive clock.
Is anyone interested in joining the team?
/
/
/

Step 1: Another POV Device

...
Yes, I know, I've reinvented wheel, since few projects are already built :
http://alan-parekh.com/projects/hard-drive-clock/
http://instruct1.cit.cornell.edu/courses/ee476/FinalProjects/s2006/ja94/Amsel%20-%20Klitinek%20Final%20Project/index.htm
http://www.ian.org/HD-Clock/
but in my opinion, original author of idea is Paul Gottlieb Nipkow who used spinning disk with holes to generate image:
http://en.wikipedia.org/wiki/Nipkow_disk

Functionally device is quite simple and it's easy to clone it using commonly available hardware and components .

Well, main ingredients for project :
- hard drive;
- index sensor;
- LEDs;
- controller;
- power supply;
- couple of weeks without sitting in a bar, watching TV, surfing Internet ;-)
...

Step 2: Hard Drive

...
From my experience, not any hard drive is appropriate for the task..
We have to conduct short function test before destroying fragile unit.;-)

At first, open hard drive and remove actuator arm with magnetic heads.
Next, connect cable and apply power.
Spindle motor should start spinning. Some of hard drive controller may refuse to work when there's no signal from magnetic heads, so spindle motor will shut off after short delay. In that case we'll have to modify controller or select another hard drive and test it again.

Hard drive I've got is external SCSI Fujitsu brand.
Power consumption 12V 0.6A, 5V 1A
Spindle speed is 4400 RPM. That's 13.64 mSec for revolution.

Drive contains five platter. For this design I've left only two. Upper disk is used for image generation, lover disk - for indexing.

I cut slot in upper disk using Dremel tool, then sanded and painted top surface black for best contrast.

Matching inner surfaces of disks are painted white for color diffusion and reflection.

Step 3: LEDs

...
For the first unit I've built, I had to make PCB with 24 red, green and blue LEDs surrounding disk, but discovery of RGB Flexible Light Strips made huge improvement in quality of light and simplicity of final unit

Here's where to get this great product from: http://www.superbrightleds.com/specs/FLS.htm

Light strip has self-adhesive backing and consists of few section with RGB LEDs and SMT resistors. All section are connected in parallel so you can cut any amount you need for your project. It requires 4 wire cable to operate. Anode is common.

Values of resistors are selected for 12V application but it's possible to replace it to work with different voltage.
I left it as is, since hard drive uses 12V.

Amazingly, 9 LEDs strip has the same length as circumference of disc so it fits perfectly inside casing.
Light strip is soft and flexible so I've made base ring from scrap plastic for reinforcement .
Ring is secured inside hard drive with hot glue.

Power consumption for 9 LEDs :
RED - 43.75mA
GREEN - 32.5mA
BLUE - 34.8mA

LEDs of one color are controlled by dedicated 2N7000 MOSFET switch.

Step 4: Index Sensor

...
Purpose of index sensor is to tell microcontroller when full disk revolution is completed.

There are many devices with identical logic output to accomplish this task. The only difference is the way sensors interact with indexing disk..
- IR photointerrupter. Requires slot or hole to be cut in disk.
- IR photoreflective sensor. Requires high contrast mark to be placed on disc surface.
- Hall sensor. Requires magnet to be secured on disk.

I've found few SS49E analog Hall sensors among my stock. It's not the best choice for this application but I've got it working.

Output of SS49 varies in proportion to the strength of the magnetic field.
Normally output is 2.5V but it's climbing up to 5V or dropping to 0V when sensor is facing corresponding pole of a magnet.

Sensor is connected as gate driver to MOSFET based switch which applies square pulses to external interrupt input of microcontroller.

Hall sensor , MOSFET and ballast resistor are assembled on a small additional PCB which is mounted in level with bottom surface of index platter.

Tiny magnet is superglued to bottom surface of index platter.

Step 5: DIY Illuminated Push Buttons

...
As seen once in MAKE magazine; LED and tactile switch are combined as illuminated button.

Another idea for poor man?
I would say It's a good opportunity to make from ordinary staff new and unique thing.
...Yes, and it's working!!!

Illuminated buttons are assembled on a additional small PCB.
Two buttons connected in parallel resemble momentary switch.
LED is sitting on top of buttons and transmits motion to the switches when pressed.
Spring shaped leads are soldered to the board.
LED motion is relatively short so it shouldn't affect integrity of electrical connection.

Buttons and LEDs are connected to digital port of microcontroller and can be controlled independently.

Step 6: Real Time Clock-calendar

...
Nice piece of hardware from Sparkfun.

This tiny assembly contains RTC chip DS1307 with I2C interface, clock crystal and back up battery.
According to Sparkfun, module will survive 9 years without external power.
I bought few modules couple years ago, but when I connected this one to microcontroller it showed correct time. Well, I have to wait 7 more years to determine if they are right ;-)

Step 7: And Finally, Big Daddy

Well, main part of device it's controller board.

Controller is assembled on two sided PCB made by heat toner transfer method.

Brain is implemented on PIC18F2320 running at 40MHz.
Firmware is written in "C".

Upon power-up mcirocontroller reads current time and date from RTC and then refreshes data every hour.

Two timers of microcontroller synchronize work of whole device.

Timer0 is dedicated to measure time of full disk revolution. This value is used to calculate precise moment for LEDs to turn ON/OFF. Because of that, clock will display correct result regardless of disk RPM.
External interrupt function resets Timer0 upon signal from index sensor.

Timer1 is connected to external 32768 Hz crystal and configured as real time clock with period 0.25sec. It's used to scan keyboard, refresh LCD, and recalculate position of clock hands.
RGB LEDs are switching in main program loop.

Keyboard contains two illuminated buttons. It's used to set correct time/data and select clock mode.

Controller is connected with external world via 8 connectors so unit can be taken apart and reassembled within seconds.

Step 8: Assembling Unit

For easy maintenance all electrical interconnections between assemblies are implemented with cables and connectors.

Since upper platter is slightly unbalanced, I had to find method to eliminate noise and vibration.
I used rubber shock absorber from old computer, mounted on custom bracket and fastened to hard drive frame.

Step 9: Improving Quality of Generated Image

To produce contrast and colorful image this devise requires proper control of light and color.
All light emitting areas should be covered and light should be directed only in required direction so I've developed some tips for this.

Top cover for hard drive is made from plastic case of old printer.
Sleeve is made from yogurt container and hotglued to top cover.
Cover and sleeve are painted black.

Step 10: Front Panel Assembly

For front subpanel I used plastic piece from case of old printer.
Front panel is made from piece of junk aluminum.

Step 11: Illuminated Clock Dial

Clock dial is made from acrylic.
Divider marks are milled on manual micromill.
Dial is illuminated by 4 blue LEDs embedded into sides.
Each LED is inserted into short slot and secured with hot glue.
All four LEDs wired in series and connected to12V.
To achieve comfortable brightness, LEDs current is limited to 5mA by 470Ohm resistor.