Saturday, November 19, 2011

Avago ADNS-9500 Up and Running

I spent most of yesterday designing, milling and building the new circuit board for the Avago ADNS-9500 chip.  It took most of today to work through all the software changes required to make it work.  It certainly has a much higher DPI capability that is pretty insane.  Moving the ball just a little jumps from the edge of one screen all they way over to the edge of the other screen (using two computer monitors).  I'm not sure I'll have much use for that in 5670 DPI mode, but it is there should I find a need for it.

From an electrical design standpoint, the ADNS-9500 is very similar to the ADNS-7550.  Changes included a new physical package layout, grounding one pin to select between 5V and 3.3V and bumping up the size of one of the capacitors.  Other than that, the two chips use exactly the same design.

From a software perspective, I had to make arrangements to download the SROM to the chip every time it boots up.  My attempts at this were pretty bad and just crashed my Teensy board.  After doing some Google searches, I found a sketch pre-made that worked like a champ.  I was able to combine it into my current software to make a working version.  I just updated the firmware software to the current version and all is working well.  There were a few minor additional changes required to make this chip do all that I had ADNS-7550 doing, but the firmware download was the biggest hurdle.  The key ended up being the need to store the SROM image in flash memory on the Teensy instead of the default SRAM since the flash has a much larger capacity. 

In addition, I'm using the taller version of the ball support on this new circuit board with a wider set of metal ball support contacts.  It is nice and silky smooth.  The three metal supports contact the ball just below the equator line.  It seems that the further I spread these out, the better the ball movement feels. 

Tuesday, November 8, 2011

Scroll Wheel Update w/Pics

Posting has been a little slow, but I have been busy every day working on this.  Going into this, I knew that the scroll wheel would be the most mechanically complex portion of this project.  All of the parts need to be made and fit together.  I have the wheel itself and the supports on either side milled out so far.  I'm working on the circuit board at this point and need to mill out the outer case.

The theory of operation is that there will be two photo transistors that will be picking up a reflected light pattern from a rotating code wheel.  I found a nice little component (GP2S60) that incorporates both the phototransistor and emitter in a tiny surface mount package.  It is called a photointerrupter, made by Sharp.  A pair of these will be used to generate a quadrature signal that will indicate how fast the wheel is turning and in what direction.  Being optical, they won't create any drag.  I'm looking for this scroll wheel to be easy to move and have no detents, like all other scroll wheels do. 

Below are some pictures from my CAD system showing the assembly of the scroll wheel:

The photointerrupters are shown in red and yellow.  The circuit board will fit in the recess window on the right.  Those photointerrupters will be surface mounted to it:

The codewheel is highlighted below.  It will be a white piece of paper with a black set of stripes printed on it.  Simply, it will be glued/stuck to the side of the wheel. 

Tuesday, November 1, 2011

Better Optical Chips Arrived from Avago

Ask and you shall receive.  I'd like to extend a big thanks to Avago Technologies for sending me samples via Fed-Ex of their ADNK-9500 kit.  I only asked for the raw chips, but they sent the lenses and a CD too!  Awesome!  I can now start doing some designs based upon this new better chip.