On Sun, 24 Oct 1999, Benno Senoner wrote:
> PS: Now if we could get one of these turntables recorded with special
> static waves (saw waves), we could add add turntable motion detection
> and get the same features as "finalscratch" on BeOS:
> scratching an audiofile in realtime using a real turntable.
> :-)
Uhm, I have just developed a sensor decoding method that could be
useful for this. It's probably overkill, as it's accurate to some 128
bits/period of the input signal with input signals of around that
resolution. It's just that I most probably can't release the
details... :-(
Anyway, I have a clue about how to do it, so I could give some hints
if needed.
And there are other ways than a special LP. For example, a quadrature
decoder; get two reflective optisensors (UV LED + photodiode in a
single package - handy! :-), and use an encoder stripe around the
turntable disk. The encoder strip should look like this:
Sensor 1: #### #### #### #### ####
Sensor 2: #### #### #### #### ####
Note: 90 degree phase diff!
Then run the "sensor 1" signal into the U/_D input of a binary
counter. (Standard chip - use 4xxx chips [CMOS], as they're less
sensitive to Vcc errors. Do *not* use buffered chips as triggers for
reading the sensors - they can start to oscillate and fry!) The
"sensor 2" signal goes to the count input of the chip. The chip is
then hooked up to a parallel port or something, so that you can read
the current value.
Of course, you may also rip out the electronics from a mouse.
(Preferably a PS/2 one, as they have 30-150 Hz update rate, as
opposed to 10-30 for serial mice...) That's two channels and some
buttons + decoder and interface - and there are drivers. :-) Remove
the LEDs and photodiodes/transistors from the mouse PCB, and replace
them with wires to the new detectors.
//David
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