From zero to one hundred
This is not a really assignment, it is a mountain view of the final project, the abstract for researchers, the executive summary for business. It shows whole troubles and successes of the final project,
Answering questions
The goal it was to make 4 stages:
1) Capture ECG (Electrocardiogram). (From USA Fab ECG to EUROPE Fab ECG)
2) Process ECG. (from basic heart beat detection to Fast Fourier Transform)
3) Show visual result (from a basic LED to a Array LED)
4) Design (goal is to make a case portable and good looking)
It was made the Fab ECG, and it works. The main problem is the noise reduction
is for USA 60Hz power supply, so I will try in second iteration to create
a new 50Hz Fab ECG for EU 50Hz power supply.
After some tries with electrodes DIY, I can't make a good electrodes so
I started to check commercial electrodes. It was very disappointing discover
that most of commercial electrodes are bad and don't stick for more than
30 minutes on the skin. Just one commercial electrodes work ok. I'have
made the cables, clip and adaptators.
Visit my final project PAGE 1 for further information
The analog signal from Fab ECG suffer a ADconvertion and a substraction.
After that, if you make a chart of digital ECG, you will see that is possible
to detect Heart Beat by threshold. I've designed the PCB and programmed
the microcontroller.
Heart beat detection it works!
Visit my final project PAGE 2 for further information
For the first iteration, I tried just with one LED. It works!
I've studied all Fab ECG components, designed the new 50Hz Fab ECG, studied
how to make an active low pass filter for 50Hz, milled and soldering all
components. But when I test it, I realize that some wire were missed. I
tried to solve it with imaginative solutions, but it doesn't work.
The best option is to redesign again the 50Hz Fab ECG with those missed
wires and milled again.
Visit my final projet PAGE 4 for further information
I decided to keep pushing about analysis of ECG. I was studying how to make the FFT with 8bits microcontrollers. I discovered that the signal that you want to make the FFT have to be stationary and the ECG it is not stationary. In that case, you have to analyze a window where the signal is almost stationary. But chose one window or another one it is not easy, because have consecuences on FFT. After some deep research, I decided to give up. It's too deep for the short period of time that we have.
Visit my final project PAGE 1 for further information
The next step is to send messages with the LED array. I was experimenting about that point. After many problems with the LED array PCB, I got the possibility of writing words that move on the led array. I made word "NO" in a slide moving from right to left. About the stage 3 it is many more that I really could imagine to achive in those few weeks.
Visit my final project PAGE 5 for further information
Inside size was fixed by the battery size, the minimum size depens on the battery size. One side of the outer case will be in contact with skin, so this part have to be ergonomic and soft. Inside the case, there are 3 departments, divided with 3 methacrylate layers. The departments are for: 1) Fab ECG, 2) Battery and 3) PCB2 Heart Beat Detector and PCB3: LED array. Complete!
Electrocardiogram capture with 60Hz Fab ECG and commercial electrodes, Heart Beat detection with PCB2, Visual result with PCB3: Array LED, Slide word on Array LED, portable case and layers to store all PCBs.
After finish my final project, I have tried to advanced a little bit more
improving the visual result (done!) and improving the Electrocardiogram
capture and processing data with 8 bit microcontroller.
Finally, I hasn't worked 50Hz Fab ECG and Fast Fourier Transform
on 8 bit microcontroller.
I think, 50Hz Fab ECG is almost done. I have studied a lot how to make
it and now I know how fix the missed wires. Could be very interesting for
Fab Community a 50Hz Fab ECG.
About FFT for 8 bit microcontroller, Neil Gershenfeld told during my final
project presentation that there are FFT libraries for 8 bit microcontroller.
This is something to check and work.
If those two questions are solved, we could capture the electrocardiogram without 50Hz power supply noise and we could work on frequency domain with ECG (that allow to work with Heart Rate Variability with all possibilities that it means).
I'm Telecommunications Engineer and all my studies have been developed
on "simulators", for me Fab Academy and specially my final project drive
me to achive hands on level: Create my own design, 3D printing, molding
and casting, and so on. About my final project, I have learned a lot of
hands on electronics, and ergonomic design for wearables.