[sdiy] LFO, analog computers

[Jim Patchell]

Matti wrote:

> Two things on my mind lately, and I was wondering if the list had anything to
> offer.
>
> 1)In trying to produce theta waves in the brain, I wondered if I couldn't simply
> set an oscillator to 4-7 Hz, instead of putting one wave with some frequency
> into one channel, and another with a difference in frequency of 4-7 Hz into the
> other. Will normal speakers/headphones output such low frequencies? What about a
> soundcard? Most give a range of 20-20kHz, but shouldn't lower frequencies come
> out fine, or amybe distorted?
>
> 2) Can capacitors be made by doping silicon, as chips are? I'm thinking, if they
> can be, a whole lot of sample and holds might be possible to make a sort of an
> analog hardrive; think : one capacitor the equivalent 32(64...) bits of data.
> Might be useful to engineers. Or musicians. Naturally, an analog CPU would be
> most useful with such a device. Has this been done? Can't this be done?
>

    Capacitors, generally, are made my putting a layer of SiO2 over silicon, and
then metalizing that.  Basically the same process as making a metal gate mosfet.
You can also make a capacitor by using a reversed biased diode junction.  I am sure
there are a lot of other ways to do this as well.  The main problem with capacitors
on a chip is size.  You can only get so many picofarads on a chip.  In fact, if I
remember correctly, the 30 pf cap that was used on the 741 for compensation was the
largest feature on the chip.  A DRAM is basically a sample and hold.  A charge is
stored on the gate of a mosfet, except if you recall, that has to be refreshed every
2 mSec or so.  There would be a lot of engineering hurdles to overcome to make an
analog memory....wait a minute, now, keep calm Harry, but if you made an analog
memory, you would end up with.......a BBD! ;^)

    -Jim

>
> Of course, I don't know very much about computer hardware.
>
> Many thanks for your time.
>
> --------------------------------------------
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> the back. A gold to lead to resurrect what's left to die.
>
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