Wednesday, 1 February 2012

POV Fun With 2.5" Hard Disk Drives

I picked up a few faulty laptop drives cheap on ebay to take to bits and use for POV projects. I haven't finished them yet, but have been tinkering over time and will post my progress as I go.

For the first one I wanted to put a row of SMD LEDs on the platter itself (or at least on a bit of PCB replacing the platter). The problem is powering the thing... I still need to play with inductively coupled coils for power transfer, but for now I decided to use batteries.

With CR1216's and 1117 regulator

I started with a couple of CR1216 cells in holders - they balanced pretty well when the disk span up and it didn't vibrate too much. Unfortunately when I built up the rest of the circuit I hit a problem.. the LEDs would start up fine but after a few seconds they had faded down to nothing. Fresh batteries - same thing.

CR1216's are 3V lithium batteries (putting out about 3.3V) so I had a 1117 5V regulator on board to give me 5V for the PIC16F688 and the LEDs. I wondered if the current draw was reducing the battery EMF right down below the drop-out voltage of the reg so basically nothing got through the regulator. However when I removed the regulator from the circuit exactly the same thing happened. I guess CR1216's just don't have the oomph for running these high power LEDs :o(

Then I removed the CR1216 holders and put a couple of LR44 holder in their places. LR44's are alkaline button cells at 1.5V and they are a bit bigger than the CR1216's so I worried a bit about their mass on the spinning disk, but it seemed I could get away with that and they didn't fly off or anything (well, maybe just the once..)

The other concern was the lower voltage. I would get 3V instead of 5V to power the LEDs, so would they light properly? They did :o) However, the 3144 hall-effect switch I was going to use for indexing needs 4.2V minimum so I could not use that. Therefore I am currently able to get some pretty, but not stable, patterns while I wait for some new hall switches to arrive (with 3V minimum supply).

With LR44's and reg removed
Once I have the new hall switch I should be able to index the position of the disk using a magnet fixed below it, then I want to display text on the platter. This is really a test... the PIC doesn't have the memory to do much and the batteries probably wont last that long, but I hope to make another with external power (either with a brush to the back of the platter - there is continuity through the hub which makes that easier - or by inductive coupling)

This clip shows it in action. The data is just a binary counter for something to display, but its pretty

From POV on laptop hdd platter

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