How to safely power Notecarrier AF?

Hi,

the Notecarrier AF has USB and 2 JST, and the Feather board (e.g. ESP32) has USB and JST. Which of these can / should be used to power the assembled dev kit? And is it safe to connect both USB ports at once? (e.g. to get debug output from the Feather and use the Blues debug terminal).

Kind regards,
Thomas

Hey @tamberg, great question! You absolutely can plug USB cables into both the AF and the ESP32 at the same time. I do this all the time during development for exactly the reason you describe: to connect directly to the Notecard over USB serial and push firmware updates to the ESP32. Both devices will draw their power directly from those ports, but both are connected to a common ground, so won’t interfere when simultaneously connected.

As for the JST connectors, we recommend powering your project through the JST port on the Notecarrier-AF and not from the ESP32 or another Feather that includes a LiPo. You’re not at risk of ruining either device by powering through the Feather JST in terms of what we have tested, but since the Notecarrier includes additional power circuitry and reverse polarity protection, you’re better off going through the JST on the Notecarrier itself.

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You mention powering the Notecarrier-AF through he JST port. I assume you mean the Battery JST port… If we needed to power the unit from an external source (a vehicle with a 12v supply), then what would you suggest? DC-DC from 12v to 5v, and into the JST battery port? But what if we also need the battery backup (lipo) ability?

@tremmert maybe this helps https://www.adafruit.com/product/4755

(It takes 12V from solar or any other source and works with feather.)

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Hmm… Thank you for the recommendation. Any other thoughts out there? The Adafruit device you recommended only supports a max of 10v input. I am wanting to power this from a 12v power source. I could add a regulator, but I wanted to see what else others might be doing.

I was thinking about using a 12v to 3.7v buck converter, but was worried about the efficiency. I am hoping this will run off a 12v battery (not sure of the size) for a couple weeks…

Also, someone else mentioned powering the board through the JST connector. Which one? The solar or battery? If I am using a 12v to 3.7v buck converter, and connect it to the battery JST connector, and then plug in my laptop to a usb port, will that be safe?

max of 10v input

Oops, you’re right. It’s for 6V solar panels, not 12V.

How about https://www.adafruit.com/product/1065

5V regulated output from 6.5 – 32VDC input

Then connect 5V to the solar JST on the note carrier AF.

Based on https://dev.blues.io/hardware/notecarrier-datasheet/notecarrier-af/

The solar charging circuit is designed for use with a 4.5-7V solar panel.

So this should work, right?

@tamberg You have found a great solution! The product fits both the max current and max voltage constraints. Additionally, you will also need to add a LiPo battery to the battery JST, so your power solution will be able to absorb the 2A burst required to power the modem if and when it connects to GSM/GPRS.

It’s worth noting, it is NOT possible to source the 2A directly from the solar input JST, because the charge circuit is only rated for 1.25A.

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@zfields, thanks! Which capacity LiPo (and solar panel, if any) do you typically use?

Hello again @tamberg,

We use 1800-2500mAh when using flat “Pouch” lipo batteries (make sure you get the polarity correct; our preference is the Adafruit LiPo), or use most any available 18650 LiPo (although our preference is Panasonic NCR18650PF because of its temperature characteristics).

Solar panel is a matter of preference and of course it depends upon how much energy you need.

Sorry for the delay between responses. This has been such a good question, we are having internal discussions which are leading to us updating our documentation. So thank you for the excellent question!

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Been looking for this answer. Thanks!