Intent
A standalone, solar-powered monitor for a coop feeder and waterer. Two float switches watch feed and water level; when either drops below its threshold, a dedicated LED (yellow for food, blue for water) lights up as a walk-up-and-check alert. No WiFi, no app — intentionally as simple as the night light, just with two sensors instead of one knob.
How it works
- An ATtiny85 spends almost all its time in power-down sleep, woken periodically by its own watchdog timer to read both float switches and drive the matching LED, then sleep again — cheap enough on average current for a small solar panel and single-cell LiPo to sustain indefinitely.
- Water sensing is a standard liquid float switch: off the shelf, unambiguous.
- Feed sensing is the open question — feed is a granular solid, not a liquid, so a true buoyancy float won't work. The plan adapts the same float-switch mechanism with a light paddle resting on the grain surface instead of floating on liquid. Should work mechanically (the reed switch only cares about arm angle, not what's holding the arm up), but it's unverified until a real bench test happens.
- An active LED flashes rather than stays solid while its resource is low — free in power terms since it's the same wake count either way, just alternating the pin.
Hardware
| Part | Role |
|---|---|
| ATtiny85V | Runs directly off the LiPo's raw voltage, no regulator needed |
| Liquid float switch | Water level — standard, off-the-shelf |
| Adapted paddle float switch | Feed level — unverified, needs a bench test with real feed |
| Small solar panel + single-cell LiPo | Power, via a dedicated solar charge controller (not a bare TP4056) |
| Yellow / blue LED | Food-low / water-low indicators |
Most parts are real, in-stock DigiKey line items. Five are still not sourced: the blue LED, both current-limit resistors, the LiPo, the solar charge-controller board, and the float switches/panel (an Amazon job — DigiKey doesn't stock those categories).
Status & next steps
- Bench-test the adapted feed switch on real grain — confirm it trips reliably
- Measure real sleep/wake current draw to size the solar panel and battery
- Source the remaining parts (blue LED, resistors, LiPo, charge controller, float switches)
- Decide the watchdog wake interval — currently drafted at 8s, the tradeoff between response time and power
- Weatherproof enclosure — a coop means dust and moisture, unlike the other two indoor projects