[HomeBrew] Shaft encoder lesson

[James C. Garland]

Richard,
I'm not familiar with the requirements of your project, but I'd 
imagine you'd need a quadrature encoder. If you turn the shaft on 
quadrature encoder at a constant rate,  the A and B outputs will 
produce square waves that are 90 degrees out of phase with each 
other. The software in the DDS microprocessor can use these two 
outputs to tell how much you've turned the shaft, and also whether it 
was turned in a CCW or CW direction. One output is sufficient to tell 
the rate of rotation, but both outputs are needed to determine the 
sense of rotation (CW or CCW).

YOu might be able to use your optical encoder in this application. 
Basically, your optical encoder will also have A and B outputs and a 
GND, but also a Vo pin, which you would normally connect ot +5V.  The 
A & B outputs would then be either 5V or 0V, depending on the shaft 
position. WIth any luck, you should be able to control your DDS with 
these outputs.

You can look up the grey code and hexdecimal codes on Google to get a 
good explanation.  I'd be very surprised if your DDS circuit used any of these.

73,

Jim Garland W8ZR


At 05:50 PM 3/28/2006, you wrote:
>** Please do NOT cross-post messages when posting to HOMEBREW **
>
>Greetings to all on list.
>I am in need of your expertise regarding mechanical shaft encoders.
>I am building a DDS VFO project and it calls for a mechanical 
>encoder with three pins.
>Output A, Com, Output B. so far so good.
>I already own an optical shaft encoder, but I do not know how to 
>adapt it to the circuit.
>
>Question:
>
>When I go to the Digikey site to order  a mechanical 
>"Grayhill"  encoder, I find they come in different flavours, such as 
>hexadecimal, 2 bit, grey, and quadrature. I have no idea what I need.
>
>The encoder will feed a 16F628,    A to  RA0,  B to RA1  and com to RB4
>
>Please-  what is the difference between the encoder types?  Am I 
>asking a question that takes a textbook chapter to answer?
>any comments appreciated
>
>Richard  VA3NDO
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