A Scroll Wheel Project - Open for Discussion
I had previously mentioned that I seem to be stuck on my current project. As I have said, I would like to keep the actual project undisclosed for the time being but I would also like help from the internets if any have useful knowledge on the matter. All help received in the comments section or otherwise will be appreciated and noted if this project ever really gets completed.
The project that I previously mentioned is one involving a scroll wheel taken from an optical mouse. For this portion of the project, I simply need to determine how the scroll wheel recognizes the difference in the direction that the wheel is turned (scroll up or scroll down). I will then use this to produce different results with a circuit of my own. The following describes my current progress and the area that I am stuck on.
I have desoldered the scroll wheel’s hardware from the circuit board and have been analyzing the outputs of the device’s three separate terminals with a multimeter to determine how the scroll wheel device recognizes which way the wheel is turned. I have observed that everyother ‘click’ (referring to a notch in the rotation) is a shorted connection between all three of the terminals, while the other notches contain a resistance value that seems to change each time I rotate another notch, no matter which way I rotate it. I have looked for some type of pattern in these varying resistance values but so far, have not found one.
Anyone know what’s going on here?
The wheel itself is a simple rotory encoder. If I recall correctly if you have three wires Red, Yellow, and Black (ground). A connection will be made alternately from Red to Black then Yellow to Black. Depending on what connection was made first you determine the direction.
Comment by c0ffee — June 5, 2006 @
This is probably a so-called quadrature encoder. If you attach a two-channel scope to the wheel you should see that one of the signals lags behind the other. This difference in phase can be used to detect which direction the wheel is turning. Try googling for ‘quadrature encoder’ and you will find better explanations. Good luck with the project!
Comment by Karl-Martin Skontorp — June 6, 2006 @
thanks! from both of these comments, I have already made some progress. Sometimes, just knowing what to google will really help. Before this post, I honestly didn’t know to google anykind of encoder, but now I have two to investigate. I’ll keep updating with progress.
Comment by brandon — June 6, 2006 @
Quadrature encoding depends on the phase of one of the sensors leading or lagging the other to determine direction. If there’s an interrupter wheel punched full of slots, and two photodetectors at 0 and 90 degrees, then that’s what you’ve got there.
Comment by Tom — August 4, 2006 @