I got the GF one of these Velleman "rolling message" kits for the GF for Christmas, which with a few minutes of training she managed to solder up herself, and likes a lot to leave messages for her roommate on when to get off her lazy butt and take out the garbage.
It's powered by a DC 9V wall wart and regulated down to 5 for the LEDs and uP, and uses a 9V battery to keep the character memory alive when unplugged.
She doesn't like that she can't just put it anywhere and gave me a "honey-do" project to rectify this.
I had some small LiPo batteries sitting around along with charger board:
and started experimenting on perfboard. Hooked up the charger to a battery and a 2-5 V boost converter breakout based on the TI TPS6120:
I thought it would be as simple as connecting the charger output to the battery and converter, and attaching a SPDT toggle switch driving a CMOS NAND flip-flop run from the battery rail to drive the converter's shutdown pin, to control power to the display after the battery is charged.
Unfortunately it seems that with the boost converter and the uncharged battery connected in parallel, the USB charger's output keels over when plugged into a port.
So it appears I need a switching arrangement, suggestions?