Re: TECH: question about optical sensors for trackballs & spinners


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Posted by Bill Lash on 11, 2001 at 4:09 PM:

In Reply to: TECH: question about optical sensors for trackballs & spinners posted by Tehrasha on 11, 2001 at 2:17 AM:

You could probably do this and get the results that you describe. You would need to divide the signal from each of the detectors by two so you would need two flip-flops per channel. You would also need to be careful about initialization, or you would have a good chance of having a channel go backwards if the circuit powered up in a particular state. A better approach might be to develop a small state machine that tracked the states from the sensors, and put out a set of signals that reacted half as fast. That might take a few more flip-flops and some logic, so you might want to consider implementing it in a PAL if you can program one.

It might be simpler yet to run the signals to microcontroller (an AVR or PIC would probably work) and write code to make sure that you sample the inputs fast enough that you catch all of the transitions, and then send out the data over a serial port or a PS2 port. There are application notes out there that basically give you the code for doing this. The problem with the processors that they use on most mice is that they are usually clocked pretty slowly, and so they miss transitions.


: One of the biggest problems with using trackballs and spinners in cabinet projects is strobing. That pain-in-the-butt phenomenon that occurs when you spin the device hard in one direction, while the sensor either stalls and doenst read the movement, or even worse, reads it backwards.

: One attempt to fix this has been to adjust the sensitivity of the emulator and simply not spin the device as much. Another was to remove the star wheel on the devices, and replace them with one that has fewer blades or holes.

: My question is, can a similar effect be done at the electronic level? For instance, wiring a JK flip-flop in toggle mode, in line with the optic lines? This would be the electronic equiv. of having a star-wheel with 50% less holes. Wouldnt it?

: It CANT be this simple, or it would have been done by now, right? Anyone played with this concept before?




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