Adding a LiPo charging shield

[onehorse]

It looks like I can separate VIN from VUSB by cutting a jumper on the Teensy 3.1 backside, and then use VUSB and AGND as input to an on-board LiPo battery charging circuit. Then when I separate from the USB cable, I still have power as long as the battery is charged and plugged into the shield. Do I have this about right. Also, what happens to VIN in this case, can I still use it as another V input? Not that I would really need it! Thanks.

 

[PaulStoffregen]

It looks like I can separate VIN from VUSB by cutting a jumper on the Teensy 3.1 backside, and then use VUSB and AGND as input to an on-board LiPo battery charging circuit. Then when I separate from the USB cable, I still have power as long as the battery is charged and plugged into the shield. Do I have this about right.

Yes, exactly.

In fact, the original Teensy 3.0 was designed that way with the intention to someday make a shield exactly like you're describing. That was 2 years ago and it's still merely an idea on the drawing board, but you're definitely thinking about it the right way.

 

[onehorse]

I am looking at the MAX1551 for a small LiPo charging add-on shield for Teensy 3.1 which is available from Sparkfun and Mouser for less than $2 each. I am not sure it is even necessary to cut the VIN and VUSB. I'll test it out when I get a few of the chips and let you know how it works. I verified I can simply connect a 4.2 V LiPo battery to VUSB and AGND and get the Teensy 3.1 and its LSM9DS0 sensor board to function. A small charging circuit would allow the battery to be essentially permanently mounted to the Teensy, and the MAX1551 has a low voltage logic output that goes HIGH when V < 3.95 V to indicate charging is needed so an LED could be added as an indicator.