Rotary Encoder

For the frequency adjustment,
use a rotary encoder with two
gray coded outputs.

Expensive
solution 1:

Rotary encoder from HP "HEDS5701-A00" Farnell
no=730944

This type has 500 steps / revolution

BUT they are expensive, from 40 to 75 US$ depending on type.

The two outputs from the encoder
looks like this

turning the knob clockwise will generate 0 - 1 - 3 - 2 - 0 and so on

turning the knob counter clockwise
will generate 0 - 2 - 3 - 1
- 0 and so on

The PIC program compare the
old value with the new value,
to find out what direction the knob was
turned.

Cheap
solution 2:

A step motor from
an old floppy drive 5 1/4
inch disk can be used,

The two windings generate voltage when the motor is turned,

The pulse relations from the two
windings is in perfect gray code,

but needs to be amplified and level converted
to fit the 5 Volt input level of the
PIC controller

This type from a TEAC drive has 200 steps / revolution

Has ball-barings and a super good feeling

Note on the picture
the small aluminium thing that was on
the 5mm axle,

to remove it simply heat
it up fast
up to 150 C use
wide screw driver to pull
it off,

don't use force to pull
it off, this
will kill the ball-barings.

Detail to mention here: the need for a big
and heawy knob on the
stepper axle,

becourse at slow turning the
magnet will push and pull
small and weak pulses,

some of them powerfull enough be seen on the output, this is removed totaly with a heawy
knob.

Also: both outputs will be at high state
everytime the knob is standing still,

so the verry
first low-pulse on output A or
B, Should be ignored in the software.

The whole floppy drive costed me under
1US$ at a HAM marked !!

This schematic is from VK6BRO, thanks alot, it's much
more simple than the first solution
I had :-)

Why not also
visit his
great homepage

Here is the PCB layout, using SMD or normal
standing up components

Download
Gerberfile

This PCB is 35 X 35 mm and
is glued on the back side
of the steppermotor,

Input connector has pinout that fits directly
to the steppers.

The output connector has the
same pinout as the HP and
BURNES encoders.

Note the BIG hole in the
center of the PCB is for the axle
that goes out on the rear
side of the
steppermotor.

This knob was turned by
OZ8LX, and then cromed !

Looks good, the weight is 330 grames of pure
cobber, it was not possible
for me to
find brass, that is much better
to work with

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