Alt-BEAM Archive

Message #04293



To: beam@sgiblab.sgi.com
From: Richard Piotter richfile@rconnect.com
Date: Sat, 05 Jun 1999 15:11:29 -0500
Subject: [alt-beam] Re: BEAMAnt Schematic corrections(tips)


XOR: Exclusive OR. If one input is on and the other is not, then an XOR
operates. The XOR drive uses an Nu neuron to sense tactile contact. When
not active, the Nu is most likely at Gnd, so when the bicore outputs
ground, the voltage on both sides of the motor are the same (no
difference) and it doesn't turn. It's like touching a lught bulb's wires
to the SAME battery post. It don't work like that. When the Bicore
outputs a high (say 5 volts if it were regulated), then the Bicore side
of the motor Is 5 volts + and the Nu side is Gnd, so there is a voltage
applied accross the Motor, and it spins, say for this example clock wise.

Here is where the XOR drive comes in. Say it bumps something and the
tactile sensord fire the Nu. Now the Nu is at 5 volts (from the previous
example). Now when the bicore output is inactive, at ground, rather than
being stopped like before, you have gnd at the bicore side of the motor
and 5 volts + at the Nu side of the motor so now the motor spins counter
clockwise (opposiste as before). when the Bicore output goes high, then
the motor has 5 volts and 5 volts on either side, and once again, is
inactive cause there is no voltage diference.

This ability makes it possible to back up from an object that the bot
runs into. no more photovore stuck in a wall or a corner!!! It'll try to
back away from obstacles with the XOR drive.

FET: Field Effect Transistor. It's a semiconductor device that though is
constructed with doped silicon as transistors and diodes and chips are,
was designed to opperate in a similar fasion as a vacuum tube. Vacuum
tubes typicaly work the opposite of a transistor, and as great as the
transistor was, the engineers had to relearn the characteristics. FETs
were the next solution, in that they opperated much like the Vacuum tube
and circuits could be modernized with less work than if they had used
transistors. FETs are still popular today. All CMOS chips are made from
microscopic MOSFETS (Metal Oxide Semiconductor-Field Effect Transistor).
Mostfets have a drain and source and a center channel of silicon. they
also have an insulator and a gate (metal plate over the insulator). The
gate acts like a capacitor (metal plate, insulator, semiconductor).
Because of the insulator and the fact that it relies on charges not
current flow to control it, it saves some power. The voltage applied to
the gate generates a charge that causes the channel's conductive area to
change by effecting the number of free electrons or "holes".

Why do I know so much bout these? I had to take a class on them! Ahhh!
They've filled my head with FETs and Thyristors!!! AHHHHHHHHHH!!! (:

I did very well in advanced digital though (my favorite class last semester).




Jason - wrote:
> i would like to know whats 'XOR driven' havent come across this word
> before and a FET too...thanks
>
> jason


Richard Piotter
richfile@rconnect.com

The Richfiles Robotics & TI web page:
http://richfiles.calc.org

For the BEAM Robotics list:
BEAM Robotics Tek FAQ
http://people.ne.mediaone.net/bushbo/beam/FAQ.html

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