At 09:47 PM 12/19/02 -0600, you wrote:
>hello,
>
>I'm looking over enclosed linear encoders, and I see there
>are two types, absolute and incremental,
>
>what does this mean?
>
>Of couse I want a 'raw' sensor that I can hook up
>my pic to, but I don't understand this term

Absolute encoder gives you position, typically in something like
a Gray code (a binary code which, like the usual, has 2^N states
for N bits, but only one bit changes at a time, which makes
things a lot easier- they can easily be converted back and
forth).

Incremental encoder gives you (usually) quadrature pulses that
you can count up/down to measure changes in position. You need to
set the reference point with a "Home" microswitch or whatever.
Some microcontrollers have hardware to handle quadrature inputs,
you can also use a (C)PLD etc. or the micro directly if the
speed requirements are modest.

There are also hybrid types- incremental with index tracks etc.

Best regards,

Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

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