[Kyle] wanted to try something new. A Persistence of Vision Clock using a CD-ROM drive.
We have covered lots of POV Clocks that make use of hard drives, but we think this is the first time we have seen a CD-ROM drive used instead. [Kyle] points out that CD-ROM drives are typically much quieter than hard drives, which is the main reason he chose the CD-ROM route.
At the heart of this project is a good old ATMEGA168 and an RGB LED strip for the lights. To measure and maintain the rotational speed of the clock [Kyle] used an IR photodiode that detects a reference mark on the disc. An elegant build of a classic POV Clock, with a new twist!
The cool thing about this project is he did not actually use the CD-ROM drive like you think he would — he chucked the spindle motor and instead is spinning the disk using the tray ejection motor! He did this so he could control the motor by PWM straight off the microcontroller, whereas the spindle motor would require an IC and a varying control signal with specific voltage amplitudes.
He also experimented with different backgrounds and background lighting, which you can see in the video after the break!
great job! Why didn’t anyone else realize this was better than an HDD, which are so loud.
I put together a NAS box with four WD Green drives and they’re so quiet that the barely audible cooling fans running at 5v instead of their rated 12v are actually louder…
you could probably get better control by using multiple references say like having a sunray pattern printed on the back something like you see used on floppy drive motors.
Very nicely done build!
I do have a comment on the reliability of the motors though: the brushless motors of HDDs as well as the discarded CD-ROM spindle in this project have life expectancy 100s (1000s perhaps) times longer than the brished motor of the tray mechanism. The tray motor is only designed for intermittent duty and the brushes will give out in short order. Unlike an HDD, which you can have spinning for 10+ years (I’m still running a 12 years old Linux server with the original drives), the brushed DC motor at the heart of this project will probably work a couple of months at best (likely much less, I just feel generous today :)
But the idea is great. I suggest the author brings back the original BLDC CD-ROM spindle motor (the controller chip to run it is on the CD-ROM’s PCB) and enjoys his nicely looking POV clock for years to come!
“whereas the spindle motor would require an IC and a varying control signal with specific voltage amplitudes”
He could have used the micro to control the brushless motor – additional IC is not a requirement.
Well, in theory, yes. In practice though the poot micro would be very busy servicing the BLDC motor and will barely have any cycles left for the clock. In order to spin this baby at about a 1200 RMPs (easy to divide by 60) for a nice POV effect, the BLDC will have to be commutated 36 times per revolution or 720 times per second. You would want to have some feedback at least to know that you’re spinning in the right direction, then there are syncro interruptor photodiode, LEDs, buttons, RTC, what have you. I’d say it’s much better to use the chip that’s already there on the CD-ROM’s PCB or simply dedicate a micro to the motor and another to the clock functions.
720 times per second is peanuts. Even on a 16 MHz CPU, that gives you 20000 cycles per interrupt. How many do you think you need ?
That site seems to have disappeared…
(http://www.wengenroth.co/projects/cd-persistence-of-vision-clock/)
Sorry about that, just after the article appeared on HaD my server went down. Took me a while to get everything straightened out. It’s back up now
“[Kyle] points out that CD-ROM drives are typically much quieter than hard drives”
I’m sure this doesn’t refer to the eject mechanism, but to the original BLDC spindle motor. Which he replaced.
If only he’d been able to find the driver bits for the BLDC somewhere somehow… oh, wait.
I’ll agree it’s not critical to this project, but it does seem like an opportunity missed.
As many of you have pointed out, I used the ejection motor rather than the spindle motor. I did this primarily because I wanted to keep this a 1-chip design. Its been running for over 4 months with no problems (hardware wise). I still have the remaining parts from the CD-ROM drive that I will eventually use to either improve upon the design and make use of the spindle or build a second clock all together.