Run OpenBCI on LiPo battery

MikeMike
edited October 2014 in Hardware
Hi, 
I was wondering if it would be possible to use OpenBCI board with a LiPo battery like https://www.sparkfun.com/products/341
I assume that the OpenBCI 8bit version runs on 5V, thus I can simply use a booster to boost 3.7V battery to 5V. Should there be any issues with that?

Thanks, 
Mike
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Comments

  • wjcroftwjcroft Mount Shasta, CA
    Mike, I'm just today trying out the Adafruit PowerBoost 500C mentioned on this post,

    http://openbci.com/forum/index.php?p=/discussion/135/lithium-battery-recommendations/p1

    I chose this because the 500C has a built in charger, low battery indicator, etc.  I'm going to keep the PowerBoost board and LiPo at a distance from the OpenBCI board.  For example in pants pocket or on belt loop.  With the 5.2 DC cable running to the OpenBCI board, clipped to my shirt near the collar or shoulder.  (I use short sensor cables, 40" long.)  That slight .2 V addition ensures any 5 V regulators are fully functional.

    The separation serves two functions: to keep the OpenBCI light as it is clipped to cloth.  And just in case there is some mild RFI / EMI radiated from the booster, the distance will eliminate that factor.   Plan to do some scope tests to see if I notice any noise coupling into sensor cables by varying the distance, close and far.

    Of course for safety you only want to do charging with the PowerBoost while you are not wearing any sensors.

    William

  • MikeMike
    Hi William,

    It would be great to hear how it goes. I would like to do the same once I get my OpenBCI... 

    Thanks,
    Mike
  • wjcroftwjcroft Mount Shasta, CA
    Mike, here's an update.

    I have been using the Adafruit Powerboost 500C with one of their lithium batteries and OpenBCI.  Seems to work just fine.  I used the live spectrogram in Brainbay to see if I could detect any interference from the 500C getting picked up by the sensor wires / amplifier.  None that I could see.  Tried positions both near and far from the OpenBCI board.  No differences seen. 

    The 500C does have a small inductor coil, from their docs I believe this is running around 700kHz.  Even with that inductor positioned right over the ADS1299 or other parts of the board, no noise was seen on the display.

    The 500C has had it's share of comments on the Adafruit boards.  I think mostly people using it in unusual circumstances.  So please take my usage as an example only.  OpenBCI project is not promoting any particular booster or charger as the "recommended" lithium power solution.

    I measured the current drawn by the OpenBCI board.  It appears to be the same regardless of whether the board is transmitting or not.  50 milliamps.  The 2500 mAH lithium cell I got from Adafruit on the same order is thus somewhat overkill.  (2500/50 = ~ 50 hours).  They also have 500 and 1200 mAH cells, which would work out to be 10 or 24 hours respectively.  The Adafruit site mentions the TI booster they use runs at about 90% efficiency.

    As one more data point, using the 4 AA cell holder with NiMH rechargables, does not work that well.  The nominal rating of these cells when charged is 1.2V, though mine were coming up to 1.3V.  1.3 * 4 = 5.2V.  Enough to satisfy the 5V regulator, but not for long.  If your NiMH's only hit 1.2V, that is 4.8V(!)  The 4 AA NiMH cells would work better with the 32 bit OpenBCI, since that uses a 3.3V regulator.

    William
  • akritihansaakritihansa
    hello there,

    i am totally confused on how to connect the pins of ADS1299 namely BIAS_IN, BIAS_INV, BIAS_OUT and BIAS_REF. what does the BIAS_ELEC do? I am desperately in need of help..
  • wjcroftwjcroft Mount Shasta, CA
    See this post,

    http://openbci.com/forum/index.php?p=/discussion/170/getting-started-confused-about-srb-and-n1p-pins/p1

    Just use the BIAS pin on the same side as the other pins you are using.  Both BIAS pins are the same signal.  The BIAS_* lines are connected appropriately INTERNALLY on the board, you don't need to worry about that.  The external pin on the header is what you want. 

    Remember, there is SEARCH box on the forum.  For example, search on 'bias' will find multiple entries.

    Regards,

    William
  • akritihansaakritihansa
    hi williams,

    thanks a lot...actually m working on a pcb and not on the kit and this time m stuck with the srb pins. actually m using a common ref electrode, so if it is connected to srb1 then shud i leave the srb2 pin floating and what bout the negative pins?? shud they be shorted externally to ground or avdd??

    thanks,
    akriti
  • wjcroftwjcroft Mount Shasta, CA
    See our V3 schematic for how Joel routed the BIAS_ lines.  Joel and Chip found that using the negative pins with SRB2 had more flexibility.  If you are not using one set of pins you could ground them.  See the V1 V2 schematic, it was not running all the lines like V3.  Note the Bias setup on V3 is superior, so don't use V2 Bias arrangement.

    You might also try searching on the TI forum,

    http://e2e.ti.com/support/data_converters/precision_data_converters/f/73/t/374626.aspx

    This conversation would be better placed in another topic.  As it is not related to the LiPo subject line.

    Thanks, William

  • biomurphbiomurph Brooklyn, NY
    @Mike,
    Yes, you can use LiPo or any other battery supply to power the OpenBCI boards.
    Just make sure that you are providing enough power for the supply requirements.
    the 8bit Board has a 5V LDO regulator for the ATmega (so we can run at 16MHz).
    the 32bit Board has a 3V3 LDO regulator.

    The boost converter discussed should work just fine. 
  • MikeMike
    Hi William, 
    I was wondering how did you connect the power-boost to the OpenBCI board? 
    Did you use the VDD pin or you just plugged it into the battery' holder location?
    I used the booster/charger before but I connected it to the Vcc, just want to make sure to not mess up the board.

    Thanks, Mike 
  • wjcroftwjcroft Mount Shasta, CA
    Mike, hi.

    You can use a couple of these JST-PH extension cords, removing the connector from one end and soldering the wires onto the 5V and GND holes of the PowerBoost 500C. Far end of the extensions just plugs into the OpenBCI. Each cable length is a half meter long. I placed the booster + battery in my pants pocket.

    http://www.adafruit.com/products/1131

    Photo of booster on top of battery, using removable double stick foam is on the bottom of this page.

    https://sites.google.com/site/biofeedbackpages/velcro-sensors

    You could actually place a smaller battery + booster closer to the OpenBCI. I put mine in the pocket to keep the OpenBCI board light enough to clip onto my shirt. I unplug the battery from the booster when not using it.

    William



  • JakeStewJakeStew
    edited March 2015
    Why not just use a proper 2S+ battery?  They're cheap and easy to come by.  Adding switching boost regulators seems like an additional, unnecessary complication.

    I'm kinda surprised that you're not seeing any noise problems from it.  Have you checked power supply ripple?  There could be some problems that end up being filtered out in the end but cause problems none the less.
  • wjcroftwjcroft Mount Shasta, CA
    edited March 2015
    Jake, the Powerboost 500C is 15 bucks. I consider that 'cheap'. It does the boosting as well as charging from a usb port. Low battery detection, etc. Check the specs on the TI boost converter (link on same page).

    http://www.adafruit.com/products/1944

    I found no interference whatsoever in my tests. I've not used multi cell Lithium packs, but for best and safest charging, don't you need to have a charger that levels each cell independently? Sounds more complex than this simple combo board and one cell. With a booster you also get the full amp hours and battery life possible from the cell. And the low battery cut-out avoids possible damage to the cell if the voltage drops too low, since Lithiums are sensitive to this.
  • brainbrain Canada
    @wjcroft

    You do need a balance charger for multi-cell lipos, but they're quite inexpensive and simple to use -- you can get a serviceable one for about five dollars on hobbyking.com. I can send links to the HK chargers I have when I'm in the same place as they are...
  • wjcroftwjcroft Mount Shasta, CA
    edited March 2015
    There is also a caution on the 32 bit board. The 3.3v regulator there can only take 6 volts maximum. (8 bit board, which has 5v regulator can handle 12v.) So...  LiPo cells are nominally 3.7v and fully charged 4.2. If you plug a two cell LiPo into the 32 bit board, that is potentially 4.2 * 2 = 8.4 volts.

    The Powerboost puts out a constant 5.2v regardless of the lithium cell voltage or charge level.

    http://openbci.com/forum/index.php?p=/discussion/157/battery-on-the-32-bit-board

  • JakeStewJakeStew
    Good info.  The regulator might be something to tweak for the future.
    In most of the electronics I'm familiar with it's common to use a 2S lipo and a buck regulator to get a 5v line.

    Maybe one of the best things to use would be an external cell phone battery recharger.  They're cheap and provide regulated 5v power with USB charging, low voltage cutoff, etc..

    I was hoping to avoid any manner of switching supply noise and run with a linear regulator though.
  • biomurphbiomurph Brooklyn, NY
    @JakeStew yes, we are going to be upgrading the 32bit Vreg on the next manufacturing run. It will be able to handle a more reasonable Vin range.
  • MikeMike
    edited April 2015
    Hi 

    Just to double check again before I connect this booster (http://www.adafruit.com/product/1944) to 8bit BCI board.
    It seems that the board is accepting 6V-12V and the booster seems to provide 5.2V - So, my question is will it work correctly? I really want to be sure that I'm not going to ruin my board by connecting this.

    Thanks, 
    Mike 
  • wjcroftwjcroft Mount Shasta, CA
    edited April 2015
    Mike, hi. Yes it's always worked fine for me. I assume there are some others using it as well.

    William

  • MikeMike
    Thanks William. 
  • nekrodezynfekatornekrodezynfekator Poznan, Poland
    It is possible to use OpenBCI with that accu? 


    That accu have lower voltage than standard battery.
  • wjcroftwjcroft Mount Shasta, CA
    re: NIMH 1.2 V cells, see this previous comment, copied below.

    As one more data point, using the 4 AA cell holder with NiMH
    rechargables, does not work that well.  The nominal rating of these
    cells when charged is 1.2V, though mine were coming up to 1.3V.  1.3 * 4
    = 5.2V.  Enough to satisfy the 5V regulator, but not for long.  If your
    NiMH's only hit 1.2V, that is 4.8V(!)  The 4 AA NiMH cells would work
    better with the 32 bit OpenBCI, since that uses a 3.3V regulator.
  • nekrodezynfekatornekrodezynfekator Poznan, Poland
    What do you think about use powerbank like this? It is safe for OpenBCI?

    https://cdn4.pcadvisor.co.uk/cmsdata/reviews/3532885/Olixar_enCharge_Power_Bank.jpg
  • wjcroftwjcroft Mount Shasta, CA
    All USB power sources such as you are showing should provide regulated 5 volts. So should work fine.

    Then again, I'd get something associated with a known quality supplier if you can. Yeah, all of this stuff is made in China, but some manufacturers cut more corners than others. Especially if it is priced so low you can't believe such a 'deal' you are getting...  :-)
  • GromitGromit
    I tried my hand at using that powerboost board with a LiPo battery and I do see quite a lot of ripple on the 5V output, something like 50 mV amplitude sawtooth, ~830 hz.

    I made a clone board recently (just the ADC) and have been powering it up using a DC supply plugged into the wall. Then I tried powering everything using the powerboost, but I surprisingly get more 60 hz noise in the raw signals than before. It's quite interesting...will check to see what could be causing it.
  • wjcroftwjcroft Mount Shasta, CA
    edited July 2015
    For switching / boost based power supplies, 1% ripple is quite normal. 1% of 5 volts is 50 millivolts.



    The 5.1 to 5.2 output voltage (plus slight ripple) of the supply should be easily flattened by the onboard linear regulators, 3.3 or 5 V.
  • GromitGromit
    Oh right, I expected some ripple but was a little surprised by the amplitude. I checked the regulated supplies for the ADS1299 and the analog supply AVDD looks fine, while there's still a slight ripple on the digital supply DVDD. This is probably due to my crappy soldering job though, I may have damaged one of the caps on the DVDD regulator.

    Also I found the source of my noise; I was getting data with the electrodes plugged into the ADS input pins, but unconnected to my body. So the electrodes acted like antennae.

    Another thing: when I have the powerboost supplying the board, I can hear a high pitched whine...I'm assuming it's some kind of coil noise coming from the inductor on the powerboost. It doesn't affect any recordings from the ADS, but the sound is a little annoying.
  • wjcroftwjcroft Mount Shasta, CA
    Gromit, thanks.

    Interesting about the whine you're hearing. The Powerboost 500C I have here is completely silent. Does the sound dampen somewhat when you press down on the coil on the board? There is a discussion forum at Adafruit for this product. You also could probably get an exchange. Another thing to try would be to use some potting compound (like silicone or epoxy) around the coil. But that would preclude your exchanging it. Any switching type supply uses a hi freq oscillator like this. The 500C supposedly is running at 700KHz; so that must get translated down into audio range like with a subharmonic.

    William


  • GromitGromit
    It's a little weird, the whine does dampen a bit when the board is moved around but I can't see any sort of pattern (pressing down sometimes helps, sometimes doesn't). Also, when the sound is more noticeable when the bluetooth radio is on so perhaps it has something to do with additional current draw.
  • JakeStewJakeStew
    High frequency whine is usually capacitors charging.  Perhaps your power system output cap is undersized or under filtered and is charging/discharging constantly.
  • qwer1304qwer1304
    For the 32b board, can I work directly off the 3.7V LiPo?
    Thx,
    David
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