Teensy 3.x Feather Adapter

[ThousandLightYears]

Hello,

I just got this adapter assembled with my Teensy 4.0 and was happy to get the teensy powered through the adapter board. On the product page, it is mentioned that the battery can be recharged via the Teensy's usb connection. What I'm wondering is if I will need to cut the VBUS-VIN trace on the teensy.

Thank you,
Sam.

[michaelmeissner]

No, you don't need to cut the VIN/VUSB trace. Basically when there is USB power, the battery is charged if needed, but the power comes from the USB line. If there is no USB power, then it will use the battery.

I wrote this some time ago about various Teeny models compatibility with the feather adapter:

• https://github.com/TeensyUser/doc/wiki/Feather-Wings

[ThousandLightYears]

If there is no USB power, then it will use the battery.

Thanks for this. Out of curiosity, does it recoginze when usb is plugged in because of the 5 volts vs 3.7/4.2 volts from the battery? Or is there some other circuitry that does this?

[michaelmeissner]

When I plug in USB, the voltage on VIN is straight from the USB plug (4.8-5.2 volts). When the USB plug is not present, the voltage is that of the battery (3.7-4.2 volts). Several of the Adafruit add-on battery chargers (BFF and trinket backpack) are designed this way.

I have to imagine there is a transistor within the adapter that prevents current coming from the battery if there is power in the VIN already.

I've used other battery chargers where you have to cut the VIN/VUSB trace, and connect VUSB to the charger power input, and VIN to the charger power output. In these chargers, the USB power is reduced as it always goes through the charging circuitry. I go back and forth as to which I prefer.

With this other charger, there is an on/off switch that prevents the Teensy from getting power, but the battery is still charged. This is useful for cosplay props where you want to charge it at night, but don't want the blinky lights running.

On the other hand, the Adafruit feather adapter doesn't need you to adapt the Teensy for the charger, and you can use normal stacking headers on the feather adapter if you don't want to attach it permanently. As a practical matter, the Adafruit feather adapter has a more solid JST connector. With the other charger, I have to solder a JST connector to the board, and I've had times where it has come off in attaching/detaching the battery.

[ThousandLightYears]

Thanks for the info Michael.