Embedded Filter Life Indicator Design

I’m building a consumer-grade device that relies on a disposable filter, and I need an embedded electronics design that reliably tells users when that filter has reached the end of its life. The core requirement is clear: once the filter’s usable period or flow-rate threshold is met, the system must alert the user that a replacement is due.

Here is what I’m expecting from you:

• Hardware design: a compact, low-cost circuit (microcontroller-based or otherwise) able to sense filter usage and I don’t want a beep sound in the hardware, I only need LED indication with red and green lights.

• Firmware: well-documented code that tracks usage time/flow and triggers the end-of-life signal with accuracy and repeatability.
• Prototype files: schematic, PCB layout, BOM, and compiled firmware ready for quick in-house testing.
• Brief validation notes: how you verified that the alert fires at the correct point.

I want to build a timer-based system in which a green LED blinks at a fixed frequency for 11 months, and after that, a red LED blinks for 1 month. The entire system should run on a coin cell battery.

The dimensions of my project will be 30 mm (length) × 26 mm (breadth) × 5 mm (depth), and the system needs to be designed within these dimensions.