Hello everybody. I hope your weekend is going swell and your spring is off to a great start. I don’t mean to rub salt in the wounds of those of you living on the coasts but we’ve been fortunate enough to have some beautiful weather here in the center of the country for the past few weeks. During that time the team has been hard at work and we have some news to share with you.
To start off, we’ve begun to work on integrating all of the subsystems into one cohesive unit. Up until this point, we’ve worked on and tested all the subsystems in part, but have yet to put the entire pipeline together to run from beginning to end. The reason that we did it in parts was to reduce the number of variables (and potential failure modes) that we're working on at one time. When you’re testing in small units and something doesn’t work how you expect it to it’s a lot easier to figure out what the problem is. We are far enough along in the process now that we can begin to put it all together and iron out any problems that may arise.
Although we have refocused on integration right now, there is still some work left to be done to improve the accuracy of the optical character recognition system. The type of camera that we’re using stretches and squishes the picture depending on how fast it is scanning and it requires some post processing in order to create an accurate image and have accurate word recognition. This is not particularly difficult but it is a trial and error process to figure out what works the best.
FCC testing: Preliminary results
Next up, we got the preliminary results back regarding the FCC testing of our hardware. The device is currently outside of FCC part 15B class B limits. The testing facility stated that there looks to be a clock frequency around 24 MHz that is getting multiplied as harmonics. This suggests that because there are multiple clocks keeping time on our boards, where the different clock frequencies match up we’re getting a spike that is putting us outside the limits acceptable for home use.
To give you a better example of what this means, imagine you have two buzzers. One buzzes every 4 seconds while the other buzzes every 12 seconds. If you start them both at the same time, the first one will buzz at the 4 second mark and again at the 8 second mark. Then, at 12 seconds, both buzzers will buzz and it will be twice as loud. That’s essentially what is going on with our hardware. Where the clocks match up we get a spike in radiated emissions that falls outside of acceptable limits.
Fortunately, we know exactly what is causing this and in all liklihood we’ll be able to write a bit of code to turn one of the clocks off and pass the test, so we’re currently working through that.
Last but not least is the case design. Like I mentioned above, we're to the point where we can begin integration of all the parts and begin testing on the nearly final form factor rather than testing each part individually. To test the full stack, the enclosure needs to be far enough along to hold everything in the correct position.
The first step was to arrange the parts in such a way that minimizes the overall size. We've done this before but Jack was able to come up with a configuration that was more compact and better overall. After that was finished we had to model the body as a solid object and shell out the inside, making sure to keep a uniform wall thickness so the part doesn’t warp due to inconsistent shrinkage as the molten plastic cools.
After we had the shell we could begin working on modeling the internal structures that secure the components in place. We modeled mounts for the camera and lens, as well as bosses that fit into the small holes on the PCBs. Once the parts are seated and the two halves snap shut, everything should fit snugly and securely.
To make sure that worked properly we sent away to have a really nice 3D print made by Shapeways.com. They use a process called selective laser sintering to create a really finely detailed 3D printed model that you can use to test fit.
This iteration of the model helped us figure out what worked well and what didn't. Overall, the size and shape were good, though we may need to extend the case a few millimeters to allow room for the cable between the camera and the camera board. It's easy to grip, weighted nicely, and the button placement is spot on. The mount for the camera could be better if it had an additional rib but the supports for the PCBs couldn't have been more perfect. The lens mount didn't work as expected. As you push the lens into the slot, it displaces the plastic causing it to spring back out. That should be a simple fix but it does need to be redesigned. We also need to add ribs to increase rigidity and create a partition on the left half to prevent the batteries from moving.
Those changes aren't that difficult to make and we should be able to get that finished this week so we can order another 3D print.
Overall, things are coming together pretty well. There are still some issues that we need to work through but they are all well within our skill set as a team. We can see the finish line ahead of us as we are sprinting toward it.