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.
Designed in KiCad v9.
Table of Contents
- Features
- Hardware Design (KiCad)
- Panel Design
- Microcontroller Pin Mapping
- Firmware Logic
- Development & Programming
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 5V Operation: Powered directly from the CNC controller's 5V rail.
Hardware Design (KiCad)
- Power: 5V DC Input (via CNC connector J4).
- Sensor Compatibility: ZJ-S401 (or similar 5V Hall-effect flow sensors).
- Output: 3-pin CNC interface (+5V, GND, ALARM_CNC). Connects directly to standard CNC active-low sinking inputs.
Panel Design
The 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 |
|---|---|---|
| 1 | FLOW_PULSE_MCU |
Input: Pulse counter from Flow Sensor (via RC Filter) |
| 2 | GND |
System Ground (VSS) |
| 3 | ALARM_TRIGGER |
Output: Drives the Gate of the 2N7002 MOSFET |
| 4 | +5V |
System Power (VDD) |
| 5 | I2C_SDA |
I2C Data (OLED Display) |
| 6 | I2C_SCL |
I2C Clock (OLED Display) |
| 7 | BUTTON_ADC |
ADC Input: 2-Button Resistor Ladder |
| 8 | SWIO |
WCH-LinkE Programming Interface |
Firmware Logic (Overview)
- Interrupts: Pin 1 counts falling edges from the flow sensor. Flow (L/min) is calculated every second.
- Failsafe: If
Current_Flow >= Threshold, Pin 3 is driven HIGH (MOSFET ON, CNC OK). IfCurrent_Flow < Threshold, Pin 3 is driven LOW (MOSFET OFF, CNC Alarm). - UI: ADC reads Pin 7 to detect button presses for adjusting the threshold.
- Storage: User-defined threshold is saved to MCU flash memory.
Development & Programming
To flash the CH32V003, you will need a WCH-LinkE programmer connected to the 3-pin SWIO header J1 (+5V, SWIO, GND).