Alt-BEAM Archive

Message #05789



To: "'beam@sgiblab.sgi.com'" beam@sgiblab.sgi.com
From: Wilf Rigter Wilf.Rigter@powertech.bc.ca
Date: Wed, 18 Aug 1999 18:59:41 -0700
Subject: [alt-beam] Re: MOSFET sensor thingy



Try these E-field circuits. The mosfet circuit has the advantage of an
adjustable operating point which can also be used to adjust =
sensitivity. The
temperature and +V / gain and set point stability is not great but it's
simple. The CMOS opamp design has good stability and is capable of =
much
higher gain by replacing the 1M feedback resistor with 100K or even =
10K. I
found that these designs provide a usable output when sensing my hand =
24
inch away from the 8 inch antenna. In the process of experimenting I
discovered a very interesting coupled oscillator design which uses the =
CMOS
opamp as a square wave oscillator tuned to 80Hz but which is locked to =
the
60 Hz E-field. The summing node is the noninverting input which is used =
for
hysteresis feedback and the antenna input. When I approach the 8 inch
antenna, from 48 inch away the frequency suddenly jumps to 120Hz and =
then
approaching closer switches to successively higher harmonics of 60 Hz. =
More
on the coupled oscillator Efield sensor later.

regards

wilf

<<...>>=20


> -----Original Message-----
> From: Richard Caudle [SMTP:richard@cqc.com]
> Sent: Monday, August 16, 1999 9:54 PM
> To: beam@sgiblab.sgi.com
> Subject: Re: MOSFET sensor thingy
>=20
> =A0
> =A0Bob Shannon < bshannon@tiac.net >wrote
> > Actually, if you use a MPF-102 rather than the 2N7000, you will =
have
> > reinvented Terry Newton's
> > electrostatic wake-up feelers on his older learning walker design.
> >=20
> > Also seach the archives for the Capaciflector sensor threads.=A0 =
Cool
> stuff!
>=20
> _____ =20
>=20
> =A0
> The MPF-102 is the FET that I didn't have.=A0 I found the circuit on =
Bill
> Beaty's Amatuer Science Website(copyright 1987).=A0 As far as the
> Capaciflector goes, the MOSFET thingy is really nothing like it.=A0 =
The
> capaciflector has a variable frequency(apples) and the MOSFET has =
variable
> voltage(oranges).=A0 This thingy dosen't seem to be electrostatically
> sensitive, but I have to work on it more before I'm willing to commit =
to
> that!
> =A0
> Richard
> =A0
> _____ =20
>=20



5790 Wed, 18 Aug 1999 20:15:34 -0700 [alt-beam] Re: MOSFET sensor thingy "'beam@sgiblab.sgi.com'" Wilf Rigter
content-type: text/plain


Just in case you didn't get it, here's the missing attachment.

<>

Wilf Rigter mailto:wilf.rigter@powertech.bc.ca


> -----Original Message-----
> From: Wilf Rigter [SMTP:Wilf.Rigter@powertech.bc.ca]
> Sent: Wednesday, August 18, 1999 7:00 PM
> To: 'beam@sgiblab.sgi.com'
> Subject: RE: MOSFET sensor thingy
>
>
> Try these E-field circuits.
>



Attachment: efield.gif

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