Okay, probably you have seen this before. You take an old hard disc, open it, remove some pieces, cut some other pieces, add a piece of sand paper and connect it to a spare computer power supply. That's it. At least that's what I thought. After 30 seconds the disc just stops spinning. That is not nice.
So how did I solve this?
Some diagnosis first: I removed the hard disc heads. Therefore the electronic isn't able to successful finish the self testing. And after a while - 30 seconds to be specific - it just stops the whole system to prevent damage. Now my hard disc has a specific chip for motor control. It's an L6269 by STM. It uses a serial communication (SPI style) to interface with the control circuit (btw 25MHz of speed). Now. If I could just interrupt this communication so that this final stop command would never arrive the motor control IC then I would be fine. I thought about a few techniques for that like adding a MOSFET and a small microcontroller or doing all the communication and control by my own self-build controller.
But I ended with the simplest of it all. That's how it's done: Communication here uses some sort of SPI interface. It uses 3 lines: Clock, Data and Enable. If one device wants to send some information to someone else it first pulls Enable on High. Now it has the attention of all other devices. And everyone else waits for the data to arrive. I just soldered this "enable"-pin to the ICs power supply. Therefore it's always on High and the final stop command never arrives. But does the motor start spinning or is there a first initial start command? Well, to be short, it just starts.
Now I could also fine-tune the motor by communicating to the motor control IC - but that's far beyond the scope of this project. Oh, one last thought. If you apply to much force on the spinning disc it becomes slow and finally the internal logic of the motor control IC stops the system. But you can grind pcb boards pretty well.
