ADS1299 EEG board with isolated CANbus, USB, prototyping, etc.

mduchmduch
edited January 2016 in Other Platforms
Hi all!

I've been working on an EEG acquisition PCB for the last couple of months, and today I received my PCB. I wanted to create a little project based on the ADS1299, and I had a couple of chips I wanted to experiment with. 

3D renders

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PCB

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So here are the broad lines!
  • PIC32 MCU
  • CAN communication : I chose CAN BUS communication because I wanted to send realtime EEG data straight into MATLAB. I had prior experience with the VNT Toolbox, and I thought it could be a good way (maybe unconventional) to send data into MATLAB. Of course the CAN BUS is isolated.
  • FTDI Serial communication : Will be used mainly for debugging with a command line interface. It could also be used with a serial communication library for data transmission. The USB interface is isolated as well.
  • Prototyping area : If I want to add chips/features/etc.
  • I'm also testing a I²C to SPI interface for the ADS1299
  • EEPROM : For saving certain parameters onboard (sample rate, etc.)

Now I guess I'll be busy soldering and programming for the next couple of months!

Let me know what you think!

Comments

  • wjcroftwjcroft Mount Shasta, CA
    @mduch, wow, very cool looking design.

    It looks like you have some onboard LiPo battery charging built in as well. Is the component at U11 some type of CANbus isolator? Which PC board fab and CAD program are you using? Will you use a reflow oven at your lab or something more hand intensive?

    Congrats,

    William

  • mduchmduch
    Thanks @wjcroft ! I didn't include onboard charging, because I felt the space, time and components requiered for a safe isolated system wouldn't be worth it. I will use an external LiPo charger and charge the batteries "offline".

    The CANbus tranceiver/isolator is U12. U11 is an isolated DC/DC converter rated for up to 5.2kV of isolation. It is more expensive that I would like, but I don't want to take any safety risks! I used Altium Designer and had the PCBs manufactured by Elecrow. I will hand solder the whole thing.

    Cheers!
  • wjcroftwjcroft Mount Shasta, CA
    Thanks. Can you mention the manufacturer / part# of your DC-DC converter? That is a good isolation figure, I think it may even meet IEC medical ratings. What's the isolation voltages on your CANbus and USB isolators. I assume those use some type of opto parts; can you tell us the usb isolator device you are using?

    How do you get your computer access to the CANbus, is that a card or usb adaptor? Is the DC-DC converter getting input voltage from the CANbus or the USB? The Molex isolated power socket for input, don't you already have your isolated power? How much does the DC-DC supply?

    Regards,

    William
  • wjcroftwjcroft Mount Shasta, CA
    Here's a review for Elecrow I ran across,


  • mduchmduch
    DC-DC converter : MEJ1S0505SC from Murata
    CANbus isolator : ISO1050DWR from TI
    USB isolator : ADuM4160 from AD

    I use a CANbus USB adapter from Kvaser (Leaf Pro or Leaf HS V2 both work with isolated CANbus). For the USB isolator, the chip can work by using the USB 5V supply on the host side, and use a different supply on the device side. In my case, the device side is powered by 3.3V. The DC-DC converter is getting supply from the 5V supply on my PCB, not the USB supply.
  • wjcroftwjcroft Mount Shasta, CA
    edited January 2016
    MDuch, thanks. Murata has that MEJ1 line, looks great.

    http://www.murata-ps.com/en/news/new-products/1926

    ---

    Yeah, I was aware of the AD isolators, A number of inexpensive USB isolators now on the market, Adafruit announced their $35 module in April 2015. Based on the Analog Devices parts. Full speed optoisolated up to 12 megabits/sec.

    http://www.adafruit.com/product/2107

    http://www.analog.com/en/products/interface-isolation/isolation/usb-isolators.html

    Based on Analog Devices' proprietary iCoupler® technology, the USB 2.0
    compliant ADuM3160 and ADuM4160 are fully isolated to 1.5 Mbps and 12
    Mbps, and have been developed to lower system cost, reduce design size,
    and decrease design time, all while meeting the most demanding medical
    and industrial standards.

    Also passes isolated power, 5v at 100ma, via onboard transformers in the Analog Devices part. But that is not very much. So your Murata converter makes more sense with your expandable breadboard approach.

    Are you planning on selling your boards? The fab prices at Elecrow seem really reasonable.

    Regards,



  • mduchmduch
    edited January 2016
    That Adafruit module is a cool little board!

    I do not plan on selling the board; a future version of this project will probably be used as an educational device at my university. I do not plan on keeping CANbus as the main communication, as it needs a somewhat expensive CANbus USB adapter. This interface will be used for speeding up the development process while I explore alternatives.
  • biomurphbiomurph Brooklyn, NY
    @mduch
    Thanks for sharing your project! The board looks great! 
    Please consider posting your project on our Community page when you get it all soldered together and tested!
    www.openbci.com/community
  • bianguolongbianguolong ShenZhen

    How is your project going? Would love to see your results

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