RadioBanter - View Single Post - QUESTION: Cheap Accurate Shaft Position Encoder

July 22nd 05, 02:43 PM

wrote:
From: xpyttl on Jul 17, 5:56 pm
"Ian White G/GM3SEK" wrote in message
...

For something like a receiver tuning control, even 256 steps/rev would
sound 'jumpy'. However, you could gear it up mechanically so that even a

Actually, 256 is getting too high in most cases. The "jumpiness" comes from
the size of the step, i.e., the number of Hz per step. Encoders between 50
and 100 are probably the easiest to deal with. You generally want to make
the step size small, like 1 or 10 Hz, but you don't want hundreds of turns
to cover the band.

I'm into the actual receiver portion of a PLL-LO-controlled
HF SW BC receiver tuning in 1 KHz steps. The PLL and its
controlling circuitry are done and a 256-step Grayhill shaft
encoder is used with a shaft encoder decoder circuit from Dr.
Robert Dennis. That decoder circuit uses 3 HCMOS DIPs for
Up/Down counters having separate Up and Down clocks. One more
HCMOS DIP gate package is required for Up/Down counters having
a single clock input and having an Up or Down mode control pin.

At very high resolutions, the pulses can come very fast,
so it gets tricky to distinguish the closure from noise.

I didn't find it so. The Dennis Decoder will allow shaft
encoder rotation rates of 150 RPM with a 240-step shaft
encoder, no problem. Pressed faster, it can handle 300 RPM
or 5 revolutions per second...quite fast tuning. It is

ADDENDA:

The decoder circuit I used was from:

http://www-personal.umich.edu/~bobde...re_decoder.pdf

Two internal time-constants were about 10 times faster than
what I'm using for the tuning control on my receiver project.
I deliberately lengthened the two internal pulses used in
decoding to better observe them on a scope.

The Dennis Decoder is indicated as originating in 1998.

[University of Michigan, not Michigan State University. :-) ]

Actually, if you want to be disgustingly cheap and easy (no machining
required) then use a wheel mouse (complete) - plug it into your radio,
and decode the wheel pulses for up/down = simple switch select and a
few gates for tuning "rate". Worth a try - its not the space shuttle
your trying to build.

73 de VK3BFA Andrew