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DIY-BAS

Do It Yourself - Bio-signal Acquisition System. Its an accesible, and friendly alternative to acquire and study complex bio-signals like EEG

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Neuroscience its a complex field, or so we may think. This is because we do not have the tools necessary to dig into our own brains. The solutions are complex, intrusive and costly. There are many Brain-Computer Interface approaches but using limited hardware with staggering prices above thousands of dollars. This makes clear that this is an elite field of study. But like many other elite fields in the past, it is not until more simple and equally powerful tools are provided to begin truly unveiling the mysteries of the universe.

So what is limiting us? well, there has not been a commercial low cost approach exploiting the processing capabilities of a normal computer. The filtering and amplification techniques are the same as used decades ago, but with some minor improvements. This modern approach is ambitious and realistic. Machine Learning algorithms can be used to reduce electronic design complexity and 3D printing can also be used to create an easier to use device.

Introduction

This project begun with the idea of a smart home, regulating environment variables according to the sleep stages you are in. But there is no reliable way of measuring that! EEG or MRI are the only accurate ways for telling the quality of a sleep. But guess what, those machines are expensive. They don't have to be. EEG is a better approach since it does not involves you to be in a hazardous magnetic field to tell whether you are asleep or thinking in the woman of your dreams. Its non intrusive, and if well designed its portable and comfortable.


Problematic

Imagine you are in a kilometer long park. This park is filled with people talking, and your buddy is at the other extreme calling out your name. Yes, it is in fact that hard to listen to an EEG signal. Static and other signals in our bodies lie around 120mV while EEG signals are in the range of 1-160uV (yes Micro Volts). But hey, technology is amazing and it is completely possible to do so at a low effort expense. My goal is to do that. And yes, it is uncomfortable, having 32 to 124 wires on your head to get a complete EEG scan? current approaches look like this:

They use that to check on your sleep. Yeah, imagine sleeping with that! The leading opensource alternative OpenBCI looks like this:

Please, i dare you to wear that to switch tabs. Ok, i am not gonna lie, its open source and it works pretty good. The alternatives above are fare more tedious to setup. But still, OpenBCI offers only a 16 channel board for almost 1000$ the cheapest of 4 Channels costs 200$ + 250$ Headset (for printed yourself option! Even though its opensource, they provide cables, electrodes and whatnot). You cant do much with 4 channels in research. But i get it, electrodes, instrumentation op-amps, and filters are expensive. But here is where my brilliant idea comes!

Solution(s) - Proposal

None, i don't have ideas.... (juust kidding)

For electrodes i found out recently some guys are making 3D printed electrodes! And this company has an interesting approach of flexible electrodes. Mix those to and i bet you have cheap, comfortable DIY electrodes. Put those comfy electrodes in a cap like the first ones and you have an ultimate massag... i mean ultimate wearable EEG cap.

For the amplification, i found a novel design from 1994 which eliminates instrumentation amplifiers, coupling filters and other amplifiers, replacing them with 3 op amps to do all of that. And there is this other paper that implements differential amplifiers in a different way relying on ICA algorithm to eliminate the use of expensive instrumentation amplifiers. See where i am going? Yes, less components, more Machine Learning! Woho!

About filtering. Come on, its 2017, everything is digital. But i will thank to ICA to Better remove particular noises such as 60Hz rather than a careless notch filter. Thanks to the last paper cited above.

For Computing. Thank God for Raspberry Pi and DSPs like Teensy (i know its not a DSP, but who cares. It does deliver and with an awesome community). I like the idea of OpenBCI to have a small board built into the helmet or cap... Lets cross our fingers that the RPi Zero Wireless would be able to handle the ML or better yet, use a ESP8266 as a serial transparent bridge between teensy or whatever ADC or DSP we put in, and a local server that can also be a Raspberry (i have serious issues about Raspberry, i'ts true love. Don't judge me!)

Modularity. About ModularEEG and CHIP... They were right on spot on modularity. I am thinking of building 3 modules.

    1. Main Board: This will handle signal multiplexing, ADC acquisition, and serial transmission.
    2. Digital Board: This board will contain one ADC with some signal multiplexers and a anti-aliasing filter. This board will be the intermediate between the main DSP and the Analog boards. The Digital boards can be stacked up creating a bus communication using something like I2C or SPI with the Main Board.
    3. Analog Board: This board will contain Op-Amps capable...
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Software&Server_Diagram.jpg

This is a conceptual Workflow-like diagram for the software services and routines running on the server side.

JPEG Image - 56.07 kB - 04/01/2017 at 11:37

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Electronics_Diagram.jpg

This is a block design Diagram of all the electronics to be implemented. This is the design for the complete model introducing more ADCs and a serial bus communication between modules.

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MultiChannelModules_Diagram.jpg

This is the block design diagram sketch for the Multi-channel Module. This module handles amplification as well as handling dc-bias and dc-coupling.

JPEG Image - 40.58 kB - 04/01/2017 at 11:37

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AnalogBoards_Diagram.jpg

This is the block design Diagram for the Analog Board Module. This Module takes care of anti-aliasing filters as well as ADC conversion and multiplexation of various signals

JPEG Image - 57.80 kB - 04/01/2017 at 11:37

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FullPlatform_Diagram.jpg

This is the Full Conceptual diagram of the entire platform. It basically shows how the Electronics and SoftwareServer Diagrams connect to each other.

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MainBoard_Diagram.jpg

This is the block design Diagram of the Main board. This board isolates the power supply and also charges a battery. The heart, a DSP (Teensy 3.2 right now), is here. It has isolated serial, WiFi, and possibly Bluetooth.

JPEG Image - 49.55 kB - 04/01/2017 at 11:37

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  • 1 × Teensy 3.2 32 Bit Arduino-Compatible Microcontroler. Has a 16bit ADC!
  • 1 × TDE-200-15 Disposable/Reusable Dry EEG Electrodes
  • 2 × LT1012 Amplifier and Linear ICs / Operational Amplifiers
  • 1 × TL062 Amplifier and Linear ICs / Operational Amplifiers
  • 1 × MEJ2D0505SC Power Management ICs / Power Supply Module
  • 2 × TLC1078 Amplifier and Linear ICs / Operational Amplifiers

  • All components arrived! AT THE SAME TIME!!!

    rodrimen04/01/2017 at 12:44 0 comments

    So, i mentioned that the components would arrive next week? Guess what...

    I forgot to mention that Teensy arrived earlier this week. But that was amazing! Mouser, Linear and Florida Research Ins arrived at the same time (not in the same box, that was just to show off). But yeah, you guessed it right...

    #LatePrograming #Procrastinate #DIY-BAS

  • First Entry!

    rodrimen03/31/2017 at 17:06 0 comments

    Let me Introduce first, I am Rodrigo Mendoza. I am studying Mechatronics Engineering at "Universidad Catoliva Boliviana - La Paz/Bolivia." Whats the purpouse of this project? I love open Source Community and i love to sleep. Yes, i love to sleep. When i first started to even think on EEG, i wanted to have my room automated to regulate my sleep making it more effective, but i did not have any reliable source to measure my sleep! Until my college was about to get a BCI applications EEG device. Well, the plan failed so i decided to stop college for a semester and dedicate to build one myself.

    The alternatives like ModularEEG, The Programable CHIP, and OpenBCI were somewhat good, but still complex build or too expensive for my budget. I noted that neither uses ICA as a base, so i started to research the field. Suddenly my vacation was gone and i was on the middle of the research. So here we are.

    My research and my ideas i think are robust and well defined. So now we begin to build it and test! The electronic components arrive this week and i am exited. I will upload the complete or partial schematics of the design some time soon. If you have any thoughts let me know. Here is my gitHub reppo, i know, its really empty. It is because i am learning how to use git and github for that matter. But dont worry, i'll learn soon enough!

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T3rr0rByte13 wrote 04/08/2017 at 22:27 point

Looks interesting, I will be interested to see the Smart Home portion of your project. Cheers!

  Are you sure? yes | no

rodrimen wrote 04/10/2017 at 21:48 point

Thanks! I will post on the logs any updates or videos on the matter. If you get any ideas on the topic, they are welcomed!

  Are you sure? yes | no

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