Circle to Square converter

[PHOBoS]

I disassembled an old printer and one thing that came out of it was a big motor. After removing the controller board
I wondered if there was some more circuitry inside because there was clearly another PCB under the 'platter'.
So I removed it and found a PCB trace coil which looks like a circular squarewave. Curious if it would produce
a useful signal I hooked up my scope and saw that it gave a nice (audible) sinewave with an amplitude of ±20mV

The first thing I did was amplify it to a max level of about 5Vpp using some opamps. The TL071 is used because
of it's high input impedance, the LM358 because it goes pretty much to GND and I wanted the output voltage to go
between 0 - 5 V. Of course the amplitude varies depending on how fast you rotate it.

Next I turned the sinewave into a square. I tried using a CD40106 first but that didn't work to well.
The CD4069UB works great, the more gates you put in series, the more the signal resembles a square wave.
But I still added some schmitt trigger inverters to square it up some more. I also used the signal to indicate
if the platter is moving or not by charging a capacitor when it moves. Initially I used a CD4040 to divide
the squarewave which got reset when the platter is idle.

So I soldered the circuit onto some perf, made a frontpanel for the connectors, a simple wooden case
and it all worked well.


However there was something I was wondering about,..
On the other side of the PCB (with the coil trace) there are 6 coils, divided in 3 pairs that are hooked up in parallel,
that together with the magnet on the platter make up the actual motor. So, could I use these to indicate the direction
the platter is spinning ? (and use a CD4029 instead of a CD4040)

I hooked up my scope again and also got a sinewave from those coils but with a larger amplitude (frequency is lower though).
So the 3 coil sets produce 3 sinewaves that are out of phase, which resembles the waveform of a rotary encoder.
Now I already had the idea that it should be possible to use some flipflop's to convert the signal of a rotary encoder into
a direction output but wasn't sure how yet. I found the answer online and as it turns out it only takes 1 D-type flipflop
to do this.

So I used 2 coil sets for a quadrature waveform and made use of the CD4069UB again to square up the signals.
Because the amplitude is already much higher (4Vpp max) I didn't need an extra opamp this time.
The flip flop then gives the directional information which controls the up/down input of a CD4029.

So I had to do a bit of resoldering and add another PCB and then there was one small problem. I already made
the panel and now had another output (direction) which i wanted to add. Originally I had two outputs that gave
the status of the platter: 'rotating' or ' idle', so I sacrificed the 'rotating' output and used it for the directional output instead.


And just in case it's not clear, it does not spin by itself, but it is used as a manual generator

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[RingMad]

Ha, cool.

This kind of thing can be done with an old hard drive too... the shiny disk spins very smoothly...
http://www.instructables.com/id/HDDJ-Turning-an-old-hard-disk-drive-into-a-rotary/

James.

[PHOBoS]

Ah yes the harddrive version, I remember that one (probably inspired me).
I thought it was more complex because it uses programmable logic,
but I see it actually works in a similar way.

hmm I do have a bunch of old harddrives,..

[DUBmatze]

hehe, thats cool!!!
you can scratch your Lunetta/ modular now ..... (i use a custom cut single side record for scratching with square and sine waves... but there is no direction out ... )

I think the sine out is cool on very big soundsystems with big subwoofers or scoops wile making some bass sweeps. (but watch your beer and your stomach at 5kw+ )

[Skrog Productions]

Nice work , Phobos , I was just thinking (an electric high speed drill with a rubber wheel in the chuck, touching the disc)