# CNC Water Flow Controller

A fail-safe water flow monitoring module designed to protect CNC spindles and laser cutter tubes. It reads impulses from a ZJ-S401 water flow sensor, displays the real-time flow rate on an I2C OLED display, and triggers an active-low alarm to the CNC controller if the flow drops below a user-defined threshold.

![Flow Controller Schema](images/Flow_Controller.svg)

![Front](images/Flow_Controller_front.png)
![Back](images/Flow_Controller_back.png)

![ZJ-S401](images/Sensor_ZJ-S401.png)

## Table of Contents
1. [Features](#features)
2. [Hardware Design (KiCad)](#hardware-design-kicad)
3. [Panel Design and GCode](#panel-design-and-gcode)
4. [Microcontroller Pin Mapping](#microcontroller-pin-mapping)
5. [Firmware Logic](#firmware-logic)
6. [Firmware Build & Flashing](#firmware-build--flashing)

## Features
* **Microcontroller:** WCH CH32V003J4M6 (RISC-V).
* **Display UI:** 8-pin connector for a custom OLED/Button panel (I2C SSD1315).
* **Adjustable Threshold:** 2-button interface (Up/Down) using an analog resistor ladder (ADC) to save MCU pins.
* **Fail-Safe Output:** N-channel MOSFET (2N7002) acting as an open-drain output. It actively pulls the CNC input to GND during normal operation. If power fails, wires break, or water stops, the connection opens and triggers the CNC alarm.
* **EMI Protection:** Hardware RC debouncing and noise filtering on the sensor input.
* **Direct 24V Operation:** Powered directly from the CNC controller's 24V rail.

## Hardware Design (KiCad)
* **Power:** 24V DC Input (via CNC connector J3).
* **Sensor Compatibility:** ZJ-S401 Water flow sensor (plastic valve body, a water rotor and a hall-effect sensor). See [the working principle of the hall water flow sensor](https://www.seeedstudio.com/blog/2020/05/11/how-to-use-water-flow-sensor-with-arduino/).
* **Output:** 3-pin CNC interface (+24V, GND, ALARM_CNC). Connects directly to standard CNC active-low sinking inputs.

## Panel Design and GCode
The [scripts](scripts) folder contains a guide to panelize the board (`Flow_Controller_Panel.kicad_pcb`) and howto generate gcode.

## Microcontroller Pin Mapping (Per Schematic)
| Pin | Schematic Net | Function | MCU Port (SOP8) |
| :--- | :--- | :--- | :--- |
| 1 | `FLOW_PULSE_MCU` | Input: Pulse counter from Flow Sensor | PD6 |
| 2 | `GND` | System Ground (VSS) | VSS |
| 3 | `ALARM_TRIGGER` | Output: Drives the Gate of the 2N7002 | PA2 |
| 4 | `+24V` | System Power (VDD) | VDD |
| 5 | `I2C_SDA` | I2C Data (OLED Display) | PC1 |
| 6 | `I2C_SCL` | I2C Clock (OLED Display) | PC2 |
| 7 | `BUTTON_ADC` | ADC Input: 2-Button Resistor Ladder | PC4 |
| 8 | `SWIO` | WCH-LinkE Programming Interface | PD1 |

## Firmware Logic (Overview)
1. **Interrupts:** Pin 1 (PD6) counts falling edges from the flow sensor. Flow (L/min) is calculated every second.
2. **Failsafe:** If `Current_Flow >= Threshold`, Pin 3 is driven **HIGH** (MOSFET ON, CNC OK). If `Current_Flow < Threshold`, Pin 3 is driven **LOW** (MOSFET OFF, CNC Alarm).
3. **UI:** ADC reads Pin 7 (PC4) to detect button presses for adjusting the threshold.
4. **Storage:** User-defined threshold is saved to MCU flash memory.

## Firmware Build & Flashing
The firmware is written in C using the lightweight `ch32fun` framework. All source files and toolchain documentation are located in the `firmware` folder.

**Step-by-step Setup:**
1. Follow the setup guide in [`firmware`](firmware) to install the RISC-V GCC toolchain and `minichlink`.
2. Connect your **WCH-LinkE** programmer to the 3-pin SWIO header `J1` (+3.3V, SWIO, GND).
3. Run `make` to compile the firmware.
4. Run `make flash` to upload the code to the CH32V003 microcontroller.