Rotary encoder

Digi-key carries phototransistors from a number of manufacturers. The last time I disemboweled a mouse the phototransistors were pretty standard looking parts. Look in the Digi-Key catalog.

You can also get LED-phototransistor pairs that are already mounted in handy little holders -- this is a good thing if you are making your own mechanical assembly, because it saves you having to make the mounts.

The HP incremental encoders - HEDS-9100 and up - in the Farnell catalogue all come with either two or three channels - the two channels are two incremental outputs in quadrature, from which any competent enigneer can get directional information, and the third channel - when provided - is an index output.

In fact most of the incremental encoders in the Farnell catalogue explicitly offer quadrature outputs, and I suspect the rest do too, even if Farnell's copy-writers haven't bothered to mention it

Perhaps you might like to reprogram the relevant bit of your brain? You seem to have posted one of those bits of information "that ain't so".

----------------- Bill Sloman, Nijmegen

You're assuming it's flash.

Eh? Quadrature incremental encoders give direction information, and have for decades.

Before you re-invent the rotary encoder, look around for an off-the-shelf solution. There are many many forms of rotary encoder packages. They come in a wide range of resolutions. Most of them have their own shaft which you would have to couple to your motor shaft. However there are also the "hollow shaft" type that can be fitted onto an existing shaft. In searching, use the term "incremental encoder".

-Robert Scott Ypsilanti, Michigan

an A,B,Z incremental type will do it.

John, incremental encoders come in Quadrature A,B,Z or Just A,Z or just A output. Maybe your thinking of absolute types generating the gray/nat binary ?

I've seen John Field's brain in action here before. There's nothing flash about it.

------------------- Bill Sloman, Nijmegen

Tim Wescott wrote:

I recall a time long ago when a Boston University graduate student put up an avertisement for someone to figure out how to calculate the rotational velocity of a disk for $50.00US using photodiodes. I was an undergrad and had never heard of quadrature, but I remember riding in his car several times from Boston to his home 40 miles out in the suburbs to work on the thing in his basement. During the trip, he would drive while I listened to a professor explaining how it works on tapes that he secretly recorded in the professor's office. I was very intrigued, but after three weeks, and having not received any money, I demanded to be paid, at which point he reluctantly gave me a check from Discover Card, which he promplty warned me just two hours after would bounce. Enraged, I burned my (his) notebook, including the design for a proportional-integral-derivative (PID) controller that I had just begun. A fight ensued where he threatened me with lawsuit, and I did my own investigation (since he and his wife were suspiciously overstressed) and discovered that I was doing his master's thesis, and I called the professor at Boston University (turned out to be his advisor) and he called the university police and started a campaign to get me expelled. What's odd is that he eventually graduated with hardly and reprimand while I was placed under investigation for 2 months by a university detective and the office for academic discipline.

-Le Chaud Lapin-

Thanks for all your help,

The type of sensor I'm looking for is specifically the type found in a ball mouse. Mainly, the (probable)price and size of the components make this method desirable. The type of rotational detector often found in a mouse consists of an led facing a small device containing 2 phototransistors situated in such a way that you can decode the direction and speed of rotation with a bit of simple programming by looking at the state of "sensor 1" and then looking whether "sensor 2" goes from light to dark or dark to light. I've tried the HEDS type complete package which is fine although expensive in the long run.

If anyone knows specifically the sensor I'm still looking for (which, if you look inside a mouse, you might see something like LD1 for the LED and LQ1 for the sensor marked on the PCB silkscreen) I'd be grateful for a part number or manufacturer to get me started.

Many thanks,

Pete

Thanks,

You're probably right. There is a fairly small incorporated assembly for under 5 pounds from Agilent. It's important for me to get the component cost right down which doesn't always give the easy solution.

Thanks again,

Pete

Nah, it's just Bill Sloman. ;-)

I think everybody pretty much knows your style - you do dynamite electronics, yet can get a little bit cynical from time to time. :-)

I'd like to think of you as an "informed optomist." :-)

Cheers! Rich

No. It was just a pun. In at least one of my dialects "flash" means much the same as "flashy", with a similar sort of implication to "scintillating", though slightly less positive - "flashy" and "flash" suggest more superficial brilliance, without real depth.

John Woodgate could probably give chapter and verse, if he were around.

-------------------- Bill Sloman, Nijmegen

My pleasure. I know you would be equally happy to field my drop-offs.

---------------- Bill Sloman, Nijmegen