STM32 Smart Irrigation System

• STM32F103
• ARM Cortex-M3
• CMSIS · zero HAL
• ADC
• I²C · SSD1306
• SysTick scheduler

What it is

A controller that keeps a plant watered on its own. It continuously reads a soil-moisture sensor and drives a pump only when the soil dries past a threshold — with hysteresis so the pump doesn't chatter, and a hard safety limit so it can never run forever. It's written bare-metal on an STM32F103: every peripheral is configured by hand from the register map, with no vendor HAL and no RTOS.

How it works

• Clock bring-up from scratch. Hand-configured the 72 MHz clock tree — PLL setup and flash wait-states — before any peripheral runs.
• Clean analog reads. Polled ADC with 16-sample burst averaging plus an integer exponential moving-average filter, so noisy soil readings become stable values.
• Safe pump control. Hysteresis around the moisture threshold, wrapped in a max-run-time safety finite-state machine that force-stops the pump on a fault.
• Local UI. An SSD1306 OLED over I²C shows live status.
• Non-blocking scheduling. A SysTick-based cooperative scheduler runs the tasks — the whole firmware image fits in under 4 KB.

Why it's built this way

Going HAL-free is deliberate: it proves I can read a reference manual and bring a chip up from a blank flash, and it keeps the image tiny and fully understood. The integer-only filtering and the safety FSM reflect real embedded discipline — no floating point where it isn't needed, and never trust an actuator without a fail-safe.