Werner--as always, you share VERY useful info. It's fascinating. I just wish this was available to a wider audience via a URL I could share. A thought:
The open and free software called "known" works well as a personal blog. I have not (yet) installed "known" but am using a public instance e.g. mine is: http://ronkjeffries.withknown.com The "known" user interface is so-so but not terrible. It is fine for blog entries and nice as a Tumbler-ish way to post photos (that's my initial experiment). I apologize if there is already a way to read qi-hardware emails via a direct URL. I am lazy. Finally, I can NOT resist a small pun. Naming software "known" is confusing. It reminds me of Donald Rumsfeld's memorable phrase. http://en.m.wikipedia.org/wiki/Unknown_unknown Ron K Jeffries On Nov 10, 2014 10:11 PM, "Werner Almesberger" <[email protected]> wrote: > I'm having a bit more fun with the capacitive sensor. As mentioned, > it didn't work very well. I first ran a series of tests to examine > whether changing the configuration of the touch sensing module > would improve the sensor's performance. There are about half a > dozen parameters to play with. From what I saw, it seems that the > parameters are about as good as they get. > > However, I noticed that one of the two channels occasionally just > went dead for a while. Closer examination revealed that bending the > cables between the two boards had something to do with that > failure, but when I touched the cable at either end with tweezers, > the sensor responded normally (any direct contact just makes it go > off the scale). > > I then suspected the battery holder. As one can see in the middle > image on > > http://downloads.qi-hardware.com/people/werner/anelok/tmp/anelok-20140712.png > one of the traces is very close to a pad. So I moved the holder a > bit, but to no avail. I then removed it completely and began to > probe the trace. Turns out that there was a tiny invisible fracture > in the trace that probably responded to bending forces from the > cable. A bit of solder bridged that gap. > > > Then DFU (USB) started to fail occasionally, with an increasing > frequency. Also here, twisting the connector one way makes things > work while twisting it the other way makes them fail. I haven't > looked into that any further yet, but it'll be interesting to find > out what's happening there. > > A boring finding would be another broken trace or a bad solder > joint. If the receptacle is damaged, that would indicate that > either the build quality of that AB connector isn't so good, or > that AB in general is not the best idea (in AB, the plug will not > be stopped by the shield when reversed and the only thing stopping > it seems to be the plastic tongue holding the contacts. Not the > most confidence-inspiring design, but who am I to question the > wisdom of the mighty masters of USB ...) > > But my principal suspect is the cheap plug. Maybe it's already worn > out after a few hundred cycles. We'll see. > > > Next, the daughter board failed completely. That one was easy to > find: one of the wires resented all the bending and snapped. Maybe > using a stranded wire (30 AWG, 7/38) wasn't such a great choice > after all. In any case, this kind of connection will want at least > an FPC in the end. > > > With all the little nuisances fixed, I could get back to wrestling > with the touch sensor. To get a better idea of what it really > measured, I marked distances on the sensor, like this ... > > http://downloads.qi-hardware.com/people/werner/anelok/tmp/brd2-touch-mm.jpg > > (The cable coming out from the back replaces the battery holder I > had removed for better access to troubled traces.) > > ... and put my index finger at various positions. This is what the > results looked like: > > http://downloads.qi-hardware.com/people/werner/anelok/tmp/touch-eval.png > > The red line is the value of the A channel (minus the long-term > average, i.e., the level when no finger is present), the green line > shows the B channel. They both look nice and linear on the > respective lower half, but each has that ugly peak about 7 mm from > the top end. This corresponds to the finger overshooting the sensor > area, i.e., the area of finger over the sensor plates decreases. > > But hey, this is roughly what the sum of A and B (blue) shows. So > let's normalize the channels with the sum. This yields the magenta > and cyan lines. They look almost too good to be true. If we add > them together, we get an even stronger signal (black). > > > When I added normalization to the algorithm, the result was quite a > bit more useful than before. The change is small enough (I also had > to cheat a bit, scale up and add a small offset, or it wouldn't > feel right): > > > https://gitorious.org/anelok/anelok/commit/e568b81f074e2678cd512cb6af0e664c47ed21f8 > > The result was still quite noisy. I then put an averaging filter > operating on positions on top of everything, and this now yields > pretty acceptable performance: > > > https://gitorious.org/anelok/anelok/commit/e225efadded2d25c8dd9c01d8fa873287bb57457 > > The filter is a bit awkward (I could probably have used an EWMA > which doesn't need to record multiple values), but it's easily > extended to chopping off samples from the beginning and the end of > the press interval, in case we get false positions when the finger > is still at a distance from the sensor. > > The touch sensor still isn't perfect but it's good enough for going > back to teaching the UI a few more tricks. > > Curious what they are ? Try the simulator ! > > http://lists.en.qi-hardware.com/pipermail/discussion/2014-August/010693.html > > - Werner > > _______________________________________________ > Qi Hardware Discussion List > Mail to list (members only): [email protected] > Subscribe or Unsubscribe: > http://lists.en.qi-hardware.com/mailman/listinfo/discussion >
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