Most optical encoders actually have two (and often more) sensors in them, so
it only takes one encoder assembly to determine direction and position, or
dial reading. The sensors, simplistically, are arranged in "quadrature" -
consider one full cycle as being 180 degrees on or high (optical window
open) and 180 degrees low (optical window closed) . The two sensors are
arranged so that one comes "on" 90 degrees, or one quarter cycle or pitch
after the other. One sensor is for counting, the other for direction of
count. Direction is determined by the state (level, or 0V - low, 5V - high)
of one channel when the other goes high (or low). If the direction of
rotation of the optical wheel results in, for example, channel one going
high when channel two is low, reversing the direction of rotation results in
channel one going high when channel two is high. The state of channel two
when channel one goes high in this case indicates the direction of
rotation, or in the case of a freq dial, the frequency going up or down.
Simple logic gating produces a steady "up" or "down" signal from the
direction sensor depending on direction.
Howie WB2AWQ
Rich McCabe wrote:
> Mark try this..
>
> http://www.cse.rmit.edu.au/design/mentoring/shaft_enc/lesson2.html
>
> ----- Original Message -----
> From: "David McClafferty" <ve1adh@yahoo.ca>
> To: "Mark Erbaugh" <mark@microenh.com>
> Cc: "Tentec Reflector" <tentec@contesting.com>
> Sent: Tuesday, August 13, 2002 3:56 PM
> Subject: Re: [TenTec] Optical Encoder operation
>
> > Hi Mark, There are two sensors looking at the slots in
> > the disc. The software looks at both and determines
> > the direction by which one it sees first.
> >
> > 73, Dave, VE1ADH
> >
> > --- Mark Erbaugh <mark@microenh.com> wrote:
> > > I believe I understand the basic operation of an
> > > optical encoder, such as the 302. As you turn the
> > > knob, a series of holes on a plate connected to the
> > > shaft generate a series of pulses which the Pegasus
> > > software counts and convert into a value indicating
> > > movement. My question is how does the Pegasus
> > > determine which way (CW or CCW) the knob is being
> > > turned?
> > >
> > > Mark
> > >
> > >
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