# Industrial Welding Machine IoT Controller Specification ## Purpose Retrofit PCB for inverter welding machines. The controller reports MQTT telemetry, arc hours, machine utilization, alarm/warning states, and GPS tracking while surviving high EMI and welding transients. ## Functional Blocks 1. Power and protection: 12V_AUX input, fuse, reverse polarity protection, 16V TVS surge clamp, common-mode/LC filtering, isolated DC-DC conversion, 5V_DIG, 3V3_DIG, and 3V3_ANA rails. 2. Main controller: ESP32-WROOM-32 module for application firmware, WiFi, ADC/GPIO, UART modem control, and local diagnostics. 3. Cellular/GNSS: SIM7600/EC200U-class LTE/GNSS modem with UART control, SIM interface, LTE antenna, GNSS antenna, and high-current local bulk capacitance. 4. Isolated digital inputs: machine ON detection from 12V auxiliary sensing and fan RPM tach input through optocoupler/RC/TVS filtering. 5. Analog and sensor inputs: Hall current sensor interface with RC + op-amp buffering to ESP32 ADC; three common-terminal NTC inputs with pull-ups, RC filtering, and ADC-compatible scaling. 6. Isolated AC voltage monitoring: three-phase voltage sensing section isolated from ESP32 using opto/isolated front-end concept and ISO_GND boundary. 7. Relay-enabled welding voltage sensing: relay contacts enable the weld-voltage divider/filter only when firmware detects Hall current above threshold. 8. Connector block: 5.08mm industrial screw terminals for power, Hall, NTC common sensors, fan tach, AC phases, and welding voltage sense. ## Selected Major Parts - ESP32-WROOM-32E/32D module for WiFi and MCU. - SIM7600E-H or EC200U LTE/GNSS module; SIM7600E-H selected as default due richer GNSS/cellular capability. - IH1205S isolated DC-DC converter for 12V to isolated 5V generation; note 1W margin is tight for modem operation, so production design should validate modem peak current and may require a higher-power 12V input module if available. - AP2112K-3.3 for local 3.3V digital regulation from 5V_DIG. - PC817/PC847 optocouplers for isolated status/tach/phase sensing. - LMV358 for Hall/analog buffering. - SMBJ16A/SMAJ16A TVS for 12V input; TVS/ESD arrays or discrete clamps at all external signal connectors. - TDK/Sunlord common-mode chokes for noisy external signal pairs and power entry. - 5.08mm Phoenix/Kefa screw terminals for industrial field wiring. ## Net Naming Power nets: 12V_AUX, 12V_PROT, 5V_DIG, 3V3_DIG, 3V3_ANA, MODEM_VBAT. Ground nets: DGND, AGND, ISO_GND, CHASSIS_SHIELD. Signals: HALL_ADC, ARC_DETECT, NTC_IGBT_ADC, NTC_TRANSFORMER_ADC, NTC_HEATSINK_ADC, NTC_COMMON, FAN_TACH_ISO, MACHINE_ON_ISO, AC_PHASE_A/B/C, WELD_V_SENSE, WELD_SENSE_EN, MODEM_TX/RX, MODEM_PWRKEY, MODEM_STATUS. ## Isolation Strategy - Welding/machine-side signals enter through screw terminals into the ISO_GND domain. - Optocouplers or isolated measurement front-ends transfer digital/phase status across the isolation boundary. - Hall and NTC low-voltage sensors may use AGND with filtered entry only if their source is already low-energy and referenced to the machine control board; otherwise isolate them using external/current transducer modules. - Maintain a routed isolation slot or keepout between ISO_GND and DGND/AGND. Do not bridge with copper pours. - If chassis bonding is required, use a controlled single-point RC/Y-cap/TVS strategy, not a direct AGND-DGND-ISO_GND short. ## PCB Stackup and Sectioning Use a 6-layer PCB for EMI margin: L1 components/signals, L2 DGND reference plane, L3 power plane, L4 signal/analog, L5 AGND/DGND controlled plane regions, L6 low-speed/connector routing. Board zones: power entry at one edge, isolated field I/O along an opposite/side edge, ESP32 at board edge with antenna overhang and copper keepout, LTE/GNSS modem near antenna connectors, analog conditioning between field connectors and MCU but away from switching power. ## Connector Recommendation Use pluggable or fixed 5.08mm screw terminals, derated by 50% for continuous current. Put GND/common first where feasible. Keep AC phase and welding voltage connectors physically separated from low-voltage sensors. ## Industrial Layout Rules - Place TVS/ESD clamps immediately after connector pins before series resistors/filter components. - Place common-mode chokes at cable entry points. - Keep relay contact/welding voltage sense and AC phase networks away from ESP32 antenna and ADC traces. - Route analog ADC traces short, guarded by AGND, with RC filters close to ADC/input buffers. - Provide no copper under ESP32 antenna on all layers and place module antenna at board edge. - Use wide power traces/pours for 12V_AUX, 5V_DIG, and modem supply; place bulk capacitance at modem supply pins. - Provide mounting holes connected to chassis/shield only if enclosure bonding strategy is defined. ## Firmware/Telemetry Requirements - Publish MQTT telemetry: machine_on, arc_on, weld_current, arc_hours, utilization, three temperatures, fan_rpm, ac_phase_present flags, weld_voltage_when_enabled, alarm/warning bitfield, GPS position. - Debounce/low-pass all opto inputs. Use Hall-current threshold plus hysteresis for arc detection and relay enable. - Do not sample idle welding voltage unless WELD_SENSE_EN relay is closed after current threshold confirmation.