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 Forum index » DIY Hardware and Software » Stickney Synthyards
Circle to Square converter
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PHOBoS



Joined: Jan 14, 2010
Posts: 5578
Location: Moon Base
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PostPosted: Sun Aug 31, 2014 3:50 pm    Post subject: Circle to Square converter
Subject description: using an old motor as a rotary controller
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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. Very Happy
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. Cool


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. Cool

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 Wink


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not drawn in the schematic is the 9V voltage regulator
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Circle to Square converter - coil trace
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"My perf, it's full of holes!"
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RingMad



Joined: Jan 15, 2011
Posts: 427
Location: Montreal, Canada
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PostPosted: Mon Sep 01, 2014 3:19 am    Post subject: Reply with quote  Mark this post and the followings unread

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.
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PHOBoS



Joined: Jan 14, 2010
Posts: 5578
Location: Moon Base
Audio files: 705

PostPosted: Mon Sep 01, 2014 4:57 am    Post subject: Reply with quote  Mark this post and the followings unread

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,..

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DUBmatze



Joined: Feb 18, 2013
Posts: 150
Location: south Germaica (schwabilon)

PostPosted: Mon Sep 01, 2014 6:40 am    Post subject: Reply with quote  Mark this post and the followings unread

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+ Wink )
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Skrog Productions



Joined: Jan 07, 2009
Posts: 1195
Location: Scottish Borders
Audio files: 155

PostPosted: Thu Sep 11, 2014 10:31 am    Post subject: Reply with quote  Mark this post and the followings unread

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