Hard Disk Drive Clock :



HDD clock : principle of operation

This video shows you what can be a HDD clock :

the operation principle is rather simple :

  • A slot is milled into the top disk platter
  • A RVB led ribbon is put around the disk platter
  • Xhen the leds are On, light is only visible just at the place wher you can see the slot
  • At every disk rotation you just have to know eaxactly where is the slot to "paint" the "clock arms"
  • Persistence Of Vision is your friend :wink:

Mechanical part

Open your HDD and remove the RW heads

Now you have to mill a slot on the platter as illustrated


Using a dremel fixed on a CNC machine you can get a clean result..

Beaware to keep the center intaact in order not to fragilize too much the platter.


Then you will have to mill the disk in order to make room to easily fix the leds around and under the platter.


The bottom of the platter is painted in white to reflct the light. The leds ribbon is glued.

Take care to leave enough place at "6 o'clock" to position the hall effect sensor. This sensor is crucial to determine precisely the slot position while the disk rotates.


A strong magnet is epoxy glued under the platter exactly at the opposite of the slot so that the hall effect sensor sees the magnet when the slot is at 12 o'clock.

Here is your disk ready to be connected with a nice electronics board

hall sensor
Command and control electronics

Electronics is based on a PIC 18F4550 microcontroler from Microchip. This 8 bits MCU is natively equiped with USB capabilities. It is then easy to connect it to a PC .

Toghether with the PIC you can find :

  • hall effect sensor UGN3503U
  • real time calendar and clock DS1307 sused to keep time when power is off
  • infra red sensor to remotely command the clock (to be done)
  • mosfets to power the leds
  • a transistor to switch On/Off the disk rotation

Click on the picture to zoom schema

All this is soldered on a PCB fixed on the backside of the disk.

PCB and schematics eagle files can be dowloaded


This video illustrates how the software works, recognizing the magnet position at any time the slot goed to 12 o' clock.

As the disk is rotating at 7200 rpm, software must be triggered at a frequency of 7200/60 = 120 Hz

All the computations to display the clock must then be done in less than 8,3 µs ... and repeated every disk turn.

To run the clock you will have to flash the PIC firmware. Here is the .hex file taht you can dowload.

There is also a PC software which is used to tune the variuos parameters :

  • setting time
  • choosing clock arms colors
  • switching display modes
  • tuning layout color intensity (red and green)

PC software is here : download PC software



Finally here is a video done with the latest firmware.

This version has the following features:

  • better clock stability
  • layout color settable
  • more clocks patterns ...