The device is powered by 2 AA batteries, a no-name regulator from eBay steps up the system voltage to 5V, the MCU is an Atmega88PA that i still had left over from another project, a 32kHz clock crystal allows the MCU to remain in a power saving sleep state for most of the time. Everything fumbled together without much planning and some hot glue. While in sleep mode, the current consumption is so low, it is not even properly measurable with my cheap DMM, so the battery should last for months.

The firmware is copypasted together from other projects I've been working on, it simply wakes up every second, increments it's uptime counter and goes back to sleep. If a button is pressed shortly, the feeding status of the corresponding cat is checked by comparing a timestamp to the uptime and accordingly displayed, red means just fed/cat almost full, after 4h the LED will light up yellow, meaning cat is half-empty, after a total of 6h the LED will light up green, meaning cat likely hungry/cleared for feeding. A long press of the button resets the internal timer of the respective cat.

The enclosure is based on this model, I just added the base in Fusion360: