Re: Arbitrary Quadrature Encoder
 

Do you have an estimate of when this may be complete?

Thanks,
Mike

Re: Arbitrary Quadrature Encoder
 

We've calculated the table of stripe sizes, and are testing to find the practical limit. We don't have an estimate yet on when we will finish that testing, as we are still making adjustments on the boards (four complete, so far).

One of the things that we were less prepared for was the relative difficulty of the testing of the SMT board. It is really easy to attach probes to just about anything on our wire-wrapped board, so we can "see" what is happening. We didn't have the foresight to add a bunch of through-hole locations to add probe points to the back side of the board, so we could test input voltage levels to the first stage op-amps.

With the move from 5mm through-hole LED's and phototransistors to surface mount equivalents, there are physical changes that we are still adjusting for. Specifically, the 5mm LED's had a 20° beam, while the 0603 package has a 120° beam. Likewise, the 5mm phototransistor had a 20° cone of high-sensitivity, while the 0603 package phototransistor has a 120° cone of sensitivity. The SMT components are better suited for a transmissive/interruptor application than the reflective one that we are doing. In practical terms, this greatly reduces the distance between the encoder strip and the encoder. Our original goal was and still is to make an encoder that has a lot of tolerance for the distance between the encoder strip or disk, and the encoder.

There are domed surface mount components that can improve our range, but they are much larger than what we can easily place on the board. Likewise, there are reflective paired sensors that have a longer range, but these are also much larger than the components we are currently using.

The easiest adjustment is to change the threshold voltage, which is what we are testing now. The next step for us is doubling our illumination, which may expand our range by ~40%. This will need a new board design, so we are applying the lessons we learned so far to a new board.

Re: Arbitrary Quadrature Encoder
 

Testing is ongoing, but is throttled by student availability. The end of the school year is always chaotic.

We refined the design a little, based on our experience with the SMT boards we made. As mentioned in my last post, we are going to double the illumination, and adjust the spacing between our detectors. We also moved the detection portion to the center of the board, to make the encoder ambidextrous.

Our board shop says we should have them next week, which is after the close of our Kickstarter project.



Speaking of Kickstarter, it has been an illuminating experience. We want this to become a COTS part that any team can use, and we do not have the funds to make this happen ourselves. We have four days left, but our funding pledges have flat-lined over the last week. Thus far, our video has been watched about 1,100 times. Of our supporters, only three have come from Chief Delphi, while half have come from people browsing through Kickstarter projects. There may be more overlap, but that's what is being reported to us.

Of course, we would like our project to be successfully funded by the crowd, but if it isn't, we will still plug away at refining and developing the device. If we repost, we will have a much better project, and a much more polished video

Re: Arbitrary Quadrature Encoder
 

Well, the Kickstarter is over. Although we didn't make our goal, we're framing this experience not as a failure, but a learning opportunity on the path to a delayed success. In hindsight, it is clear that we should have been further advanced on our SMT boards before starting, and we should have looked at a smaller first run, accepting that the unit costs would be higher.

Right now, we intend to keep the development burners going all summer, until we feel that we have an adequate encoder that meets our original goals. For us, that is essentially matching the sensing we got from our wire-wrapped prototype, but on the much more compact SMT board. Even with some setbacks, we have not fallen behind our original schedule.

Where are we now? Well, we've done a lot of testing that has shown us that the encoder can sense encoder strips of several different resolutions, but we have found a lower limit that is a little too coarse for our comfort. Specifically, as the stripe size decreases, the sensing range also decreases. The encoder becomes really picky on the clearance distance between the strip and the detectors, until a point is reached where the encoder strip only registers gray, no matter what the clearance is. There is no problem with a "native" resolution strip, other than requiring it to be a bit closer than we like. It still has a bit of flexibility on the clearance distance.

This encoder was never supposed to be high resolution, as the point was to be more flexible and forgiving than the commercial encoders. We still want to be able to use the encoder for higher-resolution detection, as it would expand the envelope of uses.

We should be getting the boards for the first slight re-design (Rev. 0.2) this week, and have already gotten a second redesign (Rev. 0.3) prepared with some different components to try to address the resolution issue. Ironically, to get to higher resolution with smaller stripe sizes, we may have to go to significantly larger components on the board, that have integrated optic features. Testing will determine our course of action, as the components for the Rev. 0.3 board will add significant cost, compared to Rev. 0.1 and 0.2.

Re: Arbitrary Quadrature Encoder
 

The world has changed so much over the last quarter of a century. I look at the FIRST program, like most mentors, and ponder what it would have been like to have this kind of competition when I was in high school. That usually leads me to consider other technical advances that I can't seem to live without today, like cell phones, laptop computers and e-mail. I realize that even those are old-tech now, replaced by smartphones, tablets, and the myriad of social interaction and language destruction technologies like texting, twitter, and FaceBook. I digress.

When I was in high school, I had no problem sending an order through the mail, and waiting weeks to receive whatever it was that I had ordered. Usually, I would wait a week, and then eagerly check the mailbox every day, to see when my goodies would show up. Usually this was an act of ritualistic disappointment, until the fateful day that my package would arrive, but I was blissfully unaware that package delivery could be done any faster.

Things took longer. I had a high-speed 1200 baud modem, and I liked it. Yes I loved it! Compared to the 110 and 300 baud modems of the time, it was blazing. I used that modem and it's successors into college, and remember when the internet was not so easy. Now I'm one of those old codgers that surfed the World Wide Web with lynx (in all of it's text-based glory) in mainframe sessions, before any of my current students were born.

I remember my first experience with FedEx, getting a letter overnight. I can't even vaguely remember one of my first e-commerce sessions, when I ordered something online, and it showed up a few days later. In the past year, I've used rapid prototype services like Protolabs to get simple parts in two days, by only sending in a STEP file.

Why I bring all of this up, is a prelude to discussing the prototype board shop that we are using for this project, OshPark.

We submitted our Cadsoft Eagle files to their online system, and their software produced the gerber and drill files for the board, and gave us immediate renderings of what the finished boards would look like. Our designs were combined with the designs of other customers, to make a full panel, and those panels were manufactured here in the U.S. Our last batch of boards was shipped to us by them on Saturday, which is about a 5-day turn-around.

We couldn't be happier with them.

In this day and age, though, it seems that the U.S. Post Office has gotten me nostalgic. I realize that this is a slightly off-week, with Memorial day on Monday, but their online tracking service has taken me back to the days of indeterminate mail delivery of my youth. We know that our boards were transferred into the custody of the USPS on Saturday, at precisely 10:07 a.m., and that they expected to deliver our boards on Tuesday (two days ago). We re-check the tracking status page hourly, a symptom of the impatience caused by the technology that we take for granted today. Nothing has arrived yet. The ritual will repeat tomorrow...

Re: Arbitrary Quadrature Encoder
 

The Post Office has delivered our boards. Unfortunately, we don't know where they have delivered them. All I know is that there are reportedly somewhere in our town, but not at any address of anyone on the team.:mad:

On the positive side, we now have all of the other components for the next revisions of our design. Rev 0.2, posted above will double the illumination and move the detectors closer together. We will actually be testing two different sets of emitters and detectors on our third board revision (Rev. 0.3). That board has been getting minor tweaks to make it more amenable to reflow soldering, rather than wave soldering. That doesn't affect our hand-work now, but will make it easier when we do move into production.

Re: Arbitrary Quadrature Encoder
 

We had a fortunate break today when a neighbor discovered our package in his mail today.

We mentioned the changes we made for this board in an earlier post. Here, you can see the differences from the first set of boards. The position of most components were adjusted in some way. Additional labeling and keying of the JP1 connector was also added. JP2 was also labeled for its function.

Board front - Rev 0.2 on left Rev 0.1 on right


Board rear - Rev 0.2 on left Rev 0.1 on right

We got some branding on this set :D

This week is graduation for much of our team. We will most likely be assembling the new boards this weekend, and testing soon afterwards.