• Hi All,
    I've managed to get a prototype working that reads from a NFC enabled glucose sensor attached to someone (Freestyle Libre to be exact) and sends the readings to an iPhone app. The idea is to turn the glucose sensor that requires the user to place the phone next to it, into a continuous glucose sensor by overlaying the device I have made and sending reading over bluetooth to the phone.

    Works great, the problem is it really needs to last at least a week, and tests so far show I'm not getting even close to this. Because it's wearable the battery supplying the power must be small.

    So far I have the iphone polling every 15 minutes. I scan for the device, subscribe to the characteristic, read the data then disconnect. I'm also putting the NFC reader card into hibernate to save power as well. I thought these measures might minimise power usage however it's not good enough.

    It's probably worth mentioning that I am supplying power from a LiPoly battery via the breakout board's voltage regulator. On the final product I will not be using the breakout board, but just the core device, supplying 3.3V via a voltage regulator on the NFC device I am using, so perhaps that will help.

    I've read quite a few other posts but nothing has helped so far.

    Is there anything else I can do on the Espruino side? Have I missed something?


  • Are you using firmware 2v01? New firmware might be a bit better.

    It's pretty hard to do this 'blind' - do you have an oscilloscope? Ideally you could get a nrf52dk and the power minute board, and it'll help to give you really good stats on what is using the power

  • I am using 2V01.
    To be honest, I'm suspecting the NFC card reader.
    I think I will pursue your suggestion. I don't have an oscilloscope at the moment, but I think this is a good time to buy one :-)

  • We'd 2019.04.03

    Does anyone know if a buck step down converter consumes less power than a voltage regulator? Could device power control be used with a GPIO pin and a MOSFET perhaps, using sleep mode?

    Is this using the MDBT42Q breakout board?

  • Hi, thanks, yes I was thinking about controlling the power to the NFC reader using the Espruino.
    Yes, for the prototype I am using MDBT42Q breakout board, but don't intend to use this in the final product because the NFC card has it's own voltage regulator which I will use to supply the bare module.

  • What does the nfc device do? Isn't that already built into the module - or is it not ble?

  • Isn't that already built into the module

    The nRF52s have what are basically programmable NFC cards. They can only be read by a reader (they can't read other cards).

    As @Robin says it may be that you could add a MOSFET to properly cut power to the NFC reader when it's not in use. You could also try and power the 3.3v directly from Espruino's 3.3v and skip out their regulator - since Espruino's one is almost certainly lower power.

    However it's probably better to get some tools to start measuring before you do too much - you could end up wasting a lot of time on stuff that has little/no effect. Even using a multimeter measuring the power drawn by the NFC's VCC line could be a good first step.

    Out of interest, what NFC reader are you using? Did you improve the existing Espruino libraries for it to allow you to read the actual NFC data and do power management? If so is that something that you might consider contributing back so I can include it as an Espruino library?

  • Thanks for this tips. I'll certainly take a look at these suggestions.
    I'm using the BM019, http://www.solutions-cubed.com/bm019/

    Yes, I do intend to share it soon.

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Maximise battery life for wearable continuous glucose monitor device

Posted by Avatar for user97106 @user97106