Smallest MDBT42Q power supply?

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  • Hello, I am looking for the smallest device for Espruino. I think that this would be the MDBT42Q Breakout board, right? What is the best way to power the breakout board? It should be as small as possible. Would you recommend a rechargeable battery and how would you connect it? What battery for powering do you recommend?

    My goal is an espruino device which is as small as possible and has a quite large battery life time. I know that a large battery lifetime would result in a larger device, so it would also be okay if the battery is quite small, but then it should be rechargeable.

    Thanks for your input in advance. If you know other really small devices which support espruino, I would appreciate if you would mention them.

  • Sat 2019.06.15

    The web page content provides sufficient information in order for size comparison.

    http://www.espruino.com/MDBT42Q
    http://www.espruino.com/Pico

    The Pico, sans USB connector tab, has a slightly smaller footprint than the MDBT42Q breakout, although the MDBT42Q is a pin row width, 0.1" wider and two pins longer.



    In the Tutorial Section: Quick Start Best Practices - increasing battery life

    http://forum.espruino.com/conversations/­324125/



    An existing forum post: Powering with a coin cell

    http://forum.espruino.com/conversations/­328173/



    As both possess onboard regulators, what about a drone battery, ~0.75"x~0.5"? Getting around the charge plug and extra wire might be problematic, and the fact a separate rechargeable board or recharger would be needed.

  • Can I simply solder a JST PHR-2 connector to a V+ and GND pin, then connect a LiPo battery (Lithium ion Polymer battery with 3.7V) to the MDBT42Q breakout board for powering from the battery?

    And for recharging the battery, simply solder a micro USB breakout board like this to other V+ and GND pins of the MDBT42Q Breakout board (VBUS -> V+, GND -> GND) and then charge it by plugging in a micro usb cable? Or is there an additional board needed for recharging like this which is soldered the same way is described?

  • If you're after Bluetooth then MDBT42Q is the smallest you can get, but as @Robin says, the Pico is smaller in some ways (but has USB, not Bluetooth).

    If you're going non-rechargeable you could add something like a 1/2 AA Lithium (Lithium Thionyl Chloride or similar) battery - those have 1000mAh+ so should realistically last you a good 5 years for normal applications. The AA size ones can be 3600mAh or so, so would last you far longer.

    Can I simply solder a JST PHR-2 connector to a V+ and GND pin, then connect a LiPo battery (Lithium ion Polymer battery with 3.7V) to the MDBT42Q breakout board for powering from the battery?

    Yes, there are even two 2mm spaced pins specifically for it - there's a small amount of info on that here: http://www.espruino.com/MDBT42Q#breakout­-board

    And for recharging

    You'd need a LiPo charger board (your second link), but yes, you'd just wire it to V+/GND and you're sorted. Don't connect USB voltage directly as that'll overcharge the LiPo battery and could be quite dangerous :)

  • you could add something like a 1/2 AA Lithium (Lithium Thionyl Chloride or similar) battery

    Interesting, thanks, never heard of this chemistry and form factor. In some datasheet it says "open-circuit voltage of 3.67 V and an operating voltage of 3.60 V" Do you connect it directly to VDD or use LDO or diode or something? nrf52832 specfications says Flexible power management 1.7 V–3.6 V supply voltage range

  • I'd just connect direct (and have done in the past) - however the MDBT42 breakout already has a regulator so it doesn't really matter anyway.

    The 'absolute maximum' voltage for the nRF52832 is something like 3.9v IIRC. 3.9v isn't something you'd want to actually go close to, but going 0.07v past their recommended voltage at max battery charge isn't going to stress the chip out too much.

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Smallest MDBT42Q power supply?

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