Finally on what’s with all these posts about Physionet and AFE4400

These slides explain it all! Basically, we have been trying to capture physiological changes associated with getting tired / falling asleep. The goal here is to have an embedded system sensing changes in heart rate over time, just to warn sleepy drivers about the potential of falling asleep while they are driving.

Progress this far: we are seeing some correlation between heart rate variability and sleepiness, but need more statistics. Device-wise, we have a test system using ECG to get RR intervals and changes in them. We have Physionet’s heart rate variability tools running on a Beaglebone black, but we still need exhaustive testing to confirm reliability.

And the current implementation is split over two Blacks because we were developing in parallel, but that can be fixed in a few days’ work (not happening until finals…)

Its very cool to see a physiological indication of potential drowsiness. If we can confirm reliability, we can warn people who might be pushing themselves to keep on the road!

Soldered most of an AFE4400 to ground…

[ AFE4400 ] [ SFH-7050 ] [ Design files on GitHub ]

So I finally took up the courage to paint solder balls onto our freshly cut PCB, but I think I placed too much solder on the thermal pad, and bam, about 5 pins are now shorted to ground. By shorted, I mean that they have about an ohm to 1k ohms to ground. That because our vias didn’t plate so the thermal pad itself isn’t really grounded. Not sure if we’ll still be able to use it to dissipate heat.

I can easily use jumper wires to wire the chip’s ground plane out (one tiny trace at pin 40 will get all the load), or we can try cutting again. I am just tempted to give this one a shot, because getting another board would take time and money.





By the way, the SFH-7050 is the coolest LED package I have come across (one notch above the reverse wingulls!) There are three tiny tiny emitters inside (I wish I had a camera to click the microscopic view…some day when my phone is fixed!)