We wanted to make the Feather HUZZAH32 easy to power both when connected to a computer as well as via battery. There's two ways to power a Feather. You can connect with a Micro USB cable (just plug into the jack) and the Feather will regulate the 5V USB down to 3.3V. You can also connect a 4.2/3.7V Lithium Polymer (Lipo/Lipoly) or Lithium Ion (LiIon) battery to the JST jack. This will let the Feather run on a rechargeable battery. When the USB power is powered, it will automatically switch over to USB for power, as well as start charging the battery (if attached) at 200mA. This happens 'hot-swap' style so you can always keep the LiPoly connected as a 'backup' power that will only get used when USB power is lost.
The above shows the Micro USB jack (left), Lipoly JST jack (top left), as well as the 3.3V regulator (to the right of the JST jack), changeover diode+transistor (below the JST jack) and the Lipoly charging circuitry (right below the regulator).
There's also a CHG LED next to the USB jack, which will light up while the battery is charging. This LED might also flicker if the battery is not connected, it's normal.
You have a lot of power supply options here! We bring out the BAT pin, which is tied to the lipoly JST connector, as well as USB which is the +5V from USB if connected. We also have the 3V pin which has the output from the 3.3V regulator. We use a 500mA peak low-dropout regulator. Please budget 250mA for the WROOM32 module. While you can get 500mA total from it, you can't do it continuously from 5V as it will overheat the regulator. We use this to power the ESP32 which draws about 200mA continuous. The good news is you can put the ESP32 into sleep and low-power modes much easier.
If you're running off of a battery, chances are you wanna know what the voltage is at! That way you can tell when the battery needs recharging. Lipoly batteries are 'maxed out' at 4.2V and stick around 3.7V for much of the battery life, then slowly sink down to 3.2V or so before the protection circuitry cuts it off. By measuring the voltage you can quickly tell when you're heading below 3.7V
Since the ESP32 has tons of ADC pins, we 'sacrifice' one for Lipoly battery monitoring. You can read half of the battery voltage off of A13. Don't forget to double the voltage you read, since there is a divider.
If you'd like to turn off the 3.3V regulator, you can do that with the EN(able) pin. Simply tie this pin to Ground and it will disable the 3V regulator. The BAT and USB pins will still be powered
The two primary ways for powering a feather are a 3.7/4.2V LiPo battery plugged into the JST port or a USB power cable.
If you need other ways to power the Feather, here's what we recommend:
- For permanent installations, a 5V 1A USB wall adapter will let you plug in a USB cable for reliable power
- For mobile use, where you don't want a LiPoly, use a USB battery pack!
- If you have a higher voltage power supply, use a 5V buck converter and wire it to a USB cable's 5V and GND input
Here's what you cannot do:
- Do not use alkaline or NiMH batteries and connect to the battery port - this will destroy the LiPoly charger and there's no way to disable the charger
- Do not use 7.4V RC batteries on the battery port - this will destroy the board
The Feather is not designed for external power supplies - this is a design decision to make the board compact and low cost. It is not recommended, but technically possible:
- Connect an external 3.3V power supply to the 3V and GND pins. Not recommended, this may cause unexpected behavior and the EN pin will no longer. Also this doesn't provide power on BAT or USB and some Feathers/Wings use those pins for high current usages. You may end up damaging your Feather.
- Connect an external 5V power supply to the USB and GND pins. Not recommended, this may cause unexpected behavior when plugging in the USB port because you will be back-powering the USB port, which could confuse or damage your computer.