I reviewed the existing specification and searched for the MCU, ADC, RTD converter, and terminals. The exact ESP32-WROOM-32S remains unresolved; I did not substitute another module.
Current state: the schematic still has 0 components and 0 nets, and no PCB layout has been created. The existing Project Specification and System Architecture remain unchanged.
Remaining work is component/datasheet/footprint verification, schematic construction, power and accuracy budgets, connector pinouts, and electrical review before layout. Your selected shared isolated analog return requires compatible sensor grounding; vibration remains an expansion interface only.
Revision A — 2026-10-10. Draft / architecture review, not approved for schematic or manufacture. SmartMaintain is a production-intent, professional low-cost IIoT predictive-maintenance retrofit for existing machines in Tunisian SMEs. This file and System Architecture define three separate PCB proposals only. No components, nets, board geometry or additional projects are authorized at this stage.
Project Overview
Three independently powered nominal 24 VDC units: acquisition, energy communications, and WiFi/LTE gateway. Monitoring only: not a machine controller, protective relay, emergency-stop or safety-control system. Existing safety systems remain independent. No industrial, EMC, radio or safety certification is claimed.
Intended Use
Install in industrial cabinets near motors, VFDs and contactors, with qualified installation, grounded/shielded field cabling and purchased DIN-rail enclosures. Capture process, temperature, vibration and electrical-energy data; diagnose abnormal operation and support maintenance decisions without controlling machines. Environmental class, temperature/humidity, condensation, altitude, ingress rating and surge exposure must be agreed before detailed design.
What the Device Should Do
Acquire four 4–20 mA and two 0–10 V slow channels with external conversion, calibration, diagnostics and fault protection.
Count four independently configurable PNP/NPN nominal 24 V digital inputs with isolation; pulse bandwidth remains sensor-dependent.
Measure a separate PT100/PT1000 3/4-wire RTD through dedicated conditioning.
Require provision for one dedicated vibration interface; sensor output choice, implementation/population, module versus onboard realization and exact bandwidth remain gated. No baseline design may omit vibration capability.
Read an externally purchased certified industrial Modbus energy meter: voltage, current, active/apparent power, power factor, frequency and imported energy only where the selected meter exposes these measurements.
Gateway polls acquisition and energy nodes, buffers timestamped quality-tagged data and publishes MQTT over TLS using WiFi or cellular according to a commissioned policy; reconnect automatically.
Report supply, sensor, link, storage and communication health; distinguish stale/invalid measurements from zero readings.
Main Features
ESP32-WROOM-32S or compatible 3.3 V module on each unit; exact manufacturer/lifecycle/temperature grade not selected. Pluggable labelled industrial screw terminals, power/status/link LEDs, programming/debug, test points, isolated protected RS485 and protected DC input on all three boards. Gateway additionally has an A7670-series modem, SIM interface, LTE RF connector/path and dedicated modem supply. Firmware provision and remote updates must not bypass authentication.
Mechanical System Architecture
Text
Industrial cabinet / DIN rail
+-- purchased SELV 24 VDC supply and separately fused distribution
+-- purchased enclosure: acquisition PCB proposal -> sensor glands/terminals
+-- purchased enclosure: energy PCB proposal -> uplink and meter cable
+-- purchased enclosure: gateway PCB proposal -> uplink, SIM access, antenna feedthrough
+-- separately purchased certified energy meter/analyzer
+-- shield/PE clamps and equipotential bonding hardware
Enclosure envelope, mounting pattern, connector pitch/clearance and antenna geometry are provisional; do not invent dimensions. Metal cabinets may require external WiFi/LTE antennas. Each unit has its own protected power input; no power distribution through the RS485 data cable by default.
Electrical System Architecture
Text
Field sensors -> acquisition conditioning/isolated domains -> ESP32 slave 10
Certified meter <-> isolated separate meter segment <-> energy ESP32 slave 20
Acquisition + energy <-> one linear isolated RS485 uplink <-> gateway ESP32 ONLY master
Gateway -> WiFi OR A7670 LTE -> MQTT/TLS -> backend/dashboard/maintenance analysis
See System Architecture for full flowchart, interface matrix, barriers and power tree. Energy is the only master on its second independent meter port; it is never a master on the uplink. No mains or CT-secondary circuit belongs on any proposed PCB.
Hardware Subsystems
Table
Unit
Required blocks
Separation / design expectation
Acquisition
protected power, ESP32, four current shunts/front ends, two voltage front ends, precision multiplexed slow ADC, dedicated RTD, four isolated DI, mandatory provision for one dedicated vibration interface, isolated uplink
Six slow inputs and RTD share a proposed isolated analog island; group isolation only, not channel-to-channel. Vibration waveform conversion is separate from the slow ADC.
Energy
protected power, ESP32, two independent isolated RS485 interfaces, diagnostics/debug
Separate UARTs, isolated supplies and cable-side references for meter and uplink. Meter does all electrical-energy measurement externally.
LTE burst current and RF must be segregated from quiet circuitry. No modem powered from MCU GPIO or an assumed adequate 3.3 V rail.
Interfaces and Connections
Nominal 24 V power on every unit; uplink A/B plus isolated reference on each unit; second A/B/reference meter port on energy; optional second sensor-master port on acquisition is a new independent segment, not multiplexing the uplink. Sensor ports: four current pairs, two voltage/reference pairs, four DI pairs with explicit polarity/mode mapping, one RTD 3/4-wire terminal group and mandatory provision for one dedicated vibration connector/interface. Vibration output choice, implementation/population, module versus onboard realization and bandwidth remain gated, not its baseline requirement. Gateway has one SIM interface, one LTE antenna path and WiFi antenna as module/enclosure require. All units retain debug TX/RX/local GND and EN/BOOT access; isolation-aware programming procedures required.
Power and Runtime Expectations
Continuous operation from purchased certified suitable 24 V SELV DIN-rail PSU(s), independently protected/fused branches. No battery/charging or outage runtime promised; buffering protects network-outage data, not guaranteed operation without DC power. 18–30 V may be considered as a provisional design-study range, not an accepted input specification. Sensor 24 V feeds default to external fused distribution, not PCB feedthrough.
Power Tree and Power Budget
Text
Each unit: external 24 V -> overcurrent + reverse-polarity + coordinated TVS + EMI filter
-> efficient buck(s) -> MCU 3.3 V / local logic
Acquisition -> isolated DC/DC -> quiet post-regulated analog/reference/ADC/RTD rails
-> separate isolated uplink supply
-> optional separate IEPE high-compliance/boost rail (not selected)
Energy -> separate isolated uplink supply AND separate isolated meter supply
Gateway -> separate isolated uplink supply
-> dedicated controlled modem buck rail + bulk/MLCC -> A7670
-> storage rail / MCU 3.3 V
External fused 24 V sensor distribution -> sensors (load not included in PCB budget)
Budget is not yet numerically established; no regulator, fuse, TVS, connector-current or PSU rating finalized. Mandatory budget load inventory: every ESP32 active/WiFi peak and idle load, LEDs/debug/logic, each isolator/transceiver, each isolated DC/DC no-load loss and efficiency, slow ADC/reference/RTD excitation/front ends, four DI field currents, chosen vibration ADC/amplifiers and IEPE excitation/boost, gateway storage writes, SIM/translator and modem attach/transmit bursts. For each rail sum simultaneous loads, startup/inrush and reserves; reflect downstream power through every regulator/isolation stage using worst-case efficiency and accepted minimum input voltage. Verify cable drop, thermal dissipation, current limiting and burst response. Unknown sensor power remains external unless a revised budget authorizes PCB distribution.
Manufacturing and Assembly Expectations
Low-cost production-intent assembled SMD boards with testable industrial terminals; final layer count and supplier/fabricator unselected. Precision shunts/reference passives require controlled substitutions and calibration records. Isolation creepage/clearance depend on required working voltage, pollution/environment and barrier class; component certification does not certify a board. Candidate parts are not a committed BOM; confirm genuine sourcing, lifecycle and footprint before capture.
Firmware-Relevant Hardware Requirements
Gateway resource proposal: UART0 debug, UART1 uplink, UART2 modem. Energy: UART0 debug plus two independent UARTs for uplink and meter. Acquisition: uplink UART, debug UART, slow isolated SPI/RTD, separate vibration SPI with DMA candidate, four counter GPIOs, diagnostics and optional sensor bus. Exact GPIOs are deliberately unassigned. Check module-exposed pins, strap behavior, flash-reserved pins, input-only restrictions, EN/BOOT, DMA/driver concurrency and storage contention before schematic. A newer compatible ESP32 requires explicit driver/DMA/GPIO assessment, not silent substitution.
Use CRC, timeout/retry/error counters, collision-free addressing, driver-enable default off and watchdog-safe startup. Local feature extraction and buffering for vibration; raw continuous multichannel streaming is not assumed feasible on the proposed uplink. MQTT/TLS certificate/time provisioning, authenticated updates, offline queue endurance and power-loss recovery are required. WiFi-first/cellular-failover is a proposed configurable default, with hysteresis and data-cost limits.
Physical Design Expectations
Separate field/quiet analog/MCU/RF/high-current power regions; preserve isolation barriers without copper bridges. Keep field ESD currents away from ADC/reference and MCU grounds. WiFi antenna keepout and metal-enclosure effects require exact module guidance. LTE controlled 50-ohm RF path/coax ground, spacing, matching provision and antenna detuning must be verified in actual layout/test; no RF-performance claim exists yet.
Important Design Decisions
Protection recovery is a required design/protection-selection gate: decide retry versus latch-off versus fuse replacement for each protected path, including firmware fault diagnostics and a safe restart policy. No recovery mode is finalized; persistent faults must not be hidden by uncontrolled restarting.
Proposed defaults, pending review: three PCBs; one linear Modbus uplink, gateway only master, acquisition address 10, energy 20; meter address 1 on separate energy-master segment; uplink 115200 8E1, meter settings independently configurable. Group-isolated analog island trades cost against compatibility with differently grounded sensors. Exactly two cable-end terminations per segment, selectable single bias location; separate shield/PE and isolated reference. External certified meter avoids mains/CT circuits. Vibration and LTE variant selection remain gated.
Assumptions
No machine actuation. No final sensor catalog, metrology accuracy, waveform bandwidth, pulse frequency, cable length, retention time, environmental limits or LTE compatibility established. Independent analog configuration does not imply independent analog grounds. Floating/incompatible sensor grounds require per-channel isolation or isolated external transmitters.
Validation and Commercialization Gates
Architecture review -> datasheet/resource/power/error-budget closure -> schematic and ERC -> PCB/DFM/DRC -> firmware -> prototype characterization -> EMC/RF/regulatory testing -> pilot installation -> production release. Validate miswiring including powered-off/negative/24 V input faults, analog accuracy over temperature, DI thresholds/leakage/pulse bandwidth, RTD lead compensation, vibration anti-aliasing/sampling, modem droop/inrush and antenna performance, isolated bus disturbances and offline recovery. Qualified laboratory/regulatory review determines applicable Tunisian and export-market requirements before claims or sale.
Existing Work and Change Notes
Read-only inspection on 2026-10-10: schematic 0 components, 0 nets, no functional groups; PCB root only, copperLayers=0, no designators. Files list initially empty. Nothing electrically reusable; all requested hardware is absent. Project name smartMaintain preserved. Revision A adds architecture-stage files only; no PCB constructed and no overall build completion claimed.