Optical Mouse Navigation

[phrontist]

A little after build season was over for the 2004 season I started thinking about new ideas for this year's season, particularly autonomous mode. I was poking around CD when I saw a post by Craig Putnam in which he mentioned he was working on an optical mouse based navigation system. What a great idea, I thought! I thought about it periodically during the off season and eventually I had come up with how I wanted to do this, and had almost everything figured out except how to interface the mouse, or mice, to the RC. So I emailed Craig Putnam and he explained his progress on making such a system and much to my delight I found that much of what he had done was what I was planning to do, so I couldn't be too far off track. He also mentioned something mind-boggling...

But before I talk about that I'd like to mention something else. When I first got this piece of information from Mr. Putnam a few days ago, I didn't tell anyone and hoped he wouldn't either. This was pretty stupid for a variety of reasons, which don't need to be enumerated. Anyway, in the past few days I've seen several posts that here that are dancing around the problem, namely the following:

• TTL Serial Port and PS/2 Mouse Interface
• External Lens for Optical Mouse
• New Serial Port Driver
• Looking for Mouse Part

I realized that a lot of people are now working on Optical Mouse Navigation, and it wouldn't be fair to not share everything. So then...

There is a chip that converts PS/2 to RS232, made specifically for interfacing PICs to mice! It's from Al-Williams and it's called the PAK-XI. It slices, it dices, it makes a mean Crème Brûlée! Mr. Putnam, a mentor from team 42, P.A.R.T.S., tipped me off to it after I emailed him about it. But wait, theres more! It's also cheap! Hey! So what's the catch? Well, it may or may not be legal.

Here are a few snippets from my correspondence with Mr. Putnam:

Originally Posted by Phrontist

Panic!

I'm really hoping I'm wrong, but isn't the PAK-XI illegal for use in
FIRST accoording to last year's rule:

<R71>Additional electronic components for use on the robot must be
currently available from or equivalent to those available from Newark
InONe (http://www.newarkinone.com), Future Active
(http://future-active.com), Radio SHack (http://www.radioshack.com) or
Digi-key Corporation (http://www.digikey.com). Additional electronic
components include any object that conducts electricity other than IFI
relays and voltage controllers, wires, connectors and solder. The
total catalogue value of additional electronic components must not
exceed $300.00 USD. This cost is counted as part of the $3,500 limit.
No single electronic component shall have a catalogue value of over
$100.00 USD

Is the whole system in dire peril, dependent on a rule change? Can it
be argued that their chip is essentially equivalent to a PIC with
special software on it? For that matter couldn't it be argued that a
massive collection of bipolar semiconducters could theoretically do
the same thing ;-)

Originally Posted by Mr. Putnam

Oh good grief! Somehow, when I started this project way back when, I had
convinced myself that the PAK chip was OK to use. Given the current rules
though, it would seem problematic.

I suspect that the PAK chip is indeed nothing more than a PIC (or
equivalent) microprocessor with the software already developed and loaded.
Whether we could get a ruling from FIRST on this at this point (before
kickoff) is probably also problematic but worth a try. I'll send them a
message tonight and see what happens.

I will continue on with this project anyway - just because it is a challenge
and useful in teaching our courses. But it will be interesting to see
whether or not it can be used on a FIRST robot. I'd sure hate to see it not
be usable due to the lack of a $5 interface chip!

Originally Posted by Phrontist

*fingers crossed*

Originally Posted by Mr. Putnam

Well, I sent my question off to FIRST last night and got a response today.
Or, more accurately, a non-response (which didn't really surprise me very
much).

As I expected, they won't comment on any possible changes in rules for the
upcoming season. That's not a surprise as it could give one team a
competetive advantage over another.

Regarding whether use of a PAK chip would have been legal last year or not -
they couldn't say.

While poking around on the Microchip web site I found some application notes
and technical briefs that may be helpful. There must be a way to communicate
with the mouse without using the PAK chip. After all, the PAK chip itself
does that and I suspect it is probably some flavor of PIC microprocessor
itself (or something equivalent). You can see some examples of how Microchip
has done that if you look at TB055 and AN956. In the latter case, they are
using USB, but switching from a PS/2-based mouse to a USB-based mouse should
be a trivial exercise.

Good luck!

(I've already ordered some of those chips, and I'm not quite sure if I'm going to go ahead using them and risk their illegality, ideally I can find another solution)

Originally Posted by Phrontist

Well, now everything has come full circle!

I initially emailed you after finding nothing on the web about this
task except for those documents on the Microchip site. Oh well.

Were you able to find C18 versions of this kind of thing, because
there is little chance that I'll be learning assembler in time to make
this thing work for shipment. Bah.

Mr. Putnam has also put together a great presentation on the topic which can be found here.

I'm currently building a prototype mouse assembly, and the problem of the moment is sufficent illumination. Here are some more snippets from my correspondance with Mr. Putnam.

Originally Posted by Phrontist

We've been scratching our heads as far as illumination goes, in your
presentation there was a picture of mighty LED cluster. Now, from
expermentation I've ascertained that the LED's in mice are modulated,
and that the CMOS will only work with images illuminated with
modulated light. How did you add more LEDS? We've thought about just
making a cluster and soldering it to the old LED terminals but fear
this will cause too much draw and upset the circuit. Your help is
greatly appreciated.

Oh, and what about using IR leds? I've seen sites on which
case-modding folks do this just to be different, but rumor also has it
that the sensor is more sensitive to infared light.

Originally Posted by Mr.Putnam

Modulated huh? Hmmm... It never occurred to me to even consider that!

I simply found and whacked in a "mighty LED cluster" (as you so succinctly
put it!) and it worked just fine. The LED clusters are replacement tail
lights that you can get for cars and trucks. I got mine from
http://www.superbrightleds.com/. They come in various "strengths" (number of
LEDs in the array) and dispersion patterns. Getting them from this source is
also a whole lot less inexpensive than going to an auto parts store
(something like 1/2 to 1/3 the price for the exact same unit!).

I don't power the cluster from the mouse for the same reason you cited. I
just run it directly from the 12V supply. Even the biggest array I have
(which is the one in the photo you saw) draws very little.

Now you've got me wondering whether I got lucky with the mouse I used. I
don't recall off-hand the manufacturer of the mouse but I'm sure I can
figure it out once I get back to my office (this is my home email address).
I *do* recall that it uses an Agilent chip, but again I can't tell you right
now which one.

Perhaps the LED is not modulated on my mouse. Or perhaps the little clear
plastic piece that fits over the *other* side of the chip (from where the
optics & floor are located) supplies enough light from the board-mounted LED
(which I left in place) to satisfy the chip. I have had a feeling that the
plastic piece was some kind of a light pipe as it seems to direct some of
the LED's light onto the back side of the chip. I think you can see that
piece in one of the shots of the circuit board in the presentation.

The web site for SuperBrightLEDs has specs on their LEDs as does the Agilent
web site for their chip. I have the details at the college, but the
wavelength of the peak output of the LED array I am using is almost exactly
what is expected by the chip. As I recall it is well inside the visible
(red) spectrum.

Originally Posted by Phrontist

The plot thickens!

Well, I simply guessed it may be modulated after waving my finger back
and forth and finding that if I did it at just the right speed I could
see several fingers. Ultra-scientific, I know. Maybe dragging out ye
olde O-Scope is in order.

We've modified a mouse chip by resolding it's LED to the same
terminals, but on the bottem of the chip. Our thinking is that when
the mouse detects a change it "brightens" the LED until a period of
non-change occurs. Thus we can see if the CMOS is picking up anything
at all by simply holding it at various heights without any optics on
the CMOS. By carefully adjusting the angle of the LED we've
ascertained that 4 inches (measured from the bottem of the chip to the
ground) is the highest we can go before the LED brightness "times out"
indicating the CMOS is detecting zilch. Now we're not putting a whole
lot of stock in this, for obvious reasons.

Here is another idea, if it is modulated, connecting the LED cluster
directly isn't the only way to modulate them acoordingly. Couldn't
some sort of solution be reached with a sort of "amplifyer"? Maybe I'm
just being daft but couldn't a semiconducter or two correctly used
modulate a larger current based on a smaller one.

Hmm, looking at your diagram in the presentation, I'm beginning to
think that you got lucky. I think a single LED is sufficient
illumination to get good data at the distance shown in your diagram.

So this is where things stand at the moment. The purpose of this thread is to have a central place for everyone working on this to talk about it. Please post anything you find that's relevant.

(Innumerable thanks to Mr. Putnam, who doesn't seem to post on CD to often. I hope he doesn't mind me quoting him! Note: These are out of chronological order, for the sake of clarity)