A trenchant analysis of the new "gaming" technology introduces readers
to the interactive toys that will soon influence an entire generation
of young users.
The material in this appendix is directly derived from a set of tutorial web pages authored by Andrew Miller. Andrew has since moved on to other pursuits (that pesky "work thing," don'cha know...), so in the interests of education, I "prettied" up his tre
The Gate acts as an antenna, so leave it unconnected.
The 1-meg resistor helps protect the FET from being harmed by any
accidental sparks to its Gate lead. The circuit will work fine
without this resistor. Just don't intentionally "zap" the Gate
wire with a charged object or your charged finger.
To test the circuit, charge up a pen or a comb on your hair, then wave it
close to the little "antenna" wire. The LED should go dark. When you
remove the electrified pen or comb, the LED should light up again.
If you suspect that humidity is very high,
test this by rubbing a balloon or a plastic object upon your arm. If the
balloon does not attract your arm hairs, humidity is too high.
This FET sensor is not an ideal educational device because it responds
differently to positive than to negative.
negative objects turn the LED off, it lights again when removed.
positive objects make the LED bright, then dark when removed.
Obtain a small capacitor with a value below 100 picofarads. Connect it
between the FET gate lead and one of the other FET leads (doesn't matter
which one.) This greatly reduces the
sensitivity of the device
Now make the circuit MORE sensitive.
Obtain an alligator clip-lead, and connect it to the Gate lead of the FET.
Let it
hang loose without touching anything. You'll find that this has vastly
increased the sensitivity of your FET circuit.
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