HM8350A View Datasheet(PDF) - Unspecified
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HM8350A Datasheet PDF : 3 Pages
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A Homebrew
Shaft Encoder
Build a shaft encoder using parts
you can salvage from dead computer mice.
By Doug Smith, KF6DX
Equipment designers often find
that digital shaft encoders are
more expensive than they
would like. Encoders also may not be
available in the angular resolutions
they desire. Here is how I designed
and built a tuning knob for my com-
puter-controlled transceiver using
readily available components and a
little persistence.
Digital Rotation Sensors:
Principles of Operation
When it comes to digital rotation
sensors, the idea is to develop digital
signals that indicate both direction
and rate of rotation. The most common
arrangement is a pair of digital signals
in quadrature. That is, two digital sig-
225 Main St
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kf6dx@arrl.org
nals having a 90° phase relationship
(see Fig 1). When the shaft is rotating
in one direction, signal A leads signal
B; when rotating in the opposite direc-
tion, signal B leads signal A.
It is easy to determine the direction of
rotation using an edge-clocked D flip-
flop (see Fig 2). Applying signal A to the
flip-flop’s clock input and signal B to its
data input, signal B is low at signal A’s
rising edge when rotation occurs in one
direction; it is high when rotation is in
the opposite direction. The flip-flop’s
output signal, Q, therefore indicates the
direction of rotation. Such a direction
signal, combined with the rate of one of
the signals, A or B, yields the direction
and speed of rotation.
Of Mice and Men
John Steinbeck is a better “read,” but
the method described above is exactly
what happens inside your computer
mouse or trackball. Movement of the
Fig 1—Desired shaft encoder output
signals A and B.
Fig 2—A rising-edge-clocked D flip-flop
decodes rotation direction.
Mar/Apr 2002 1
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