Dual CAN STM32 ESP32 Gateway

About the project

1. Project overview We are looking for an electronics design engineer to develop a controller / telematics module for installation in construction machinery (excavators, loaders, road-building equipment). The device acts as a gateway between the machine's CAN buses and a Wi-Fi network — collecting data from two independent CAN buses, processing it locally, and exposing it over Wi-Fi to a service application or telematics backend. Target architecture: STM32 — main MCU: handles both CAN buses, application logic, I/O ESP32 — Wi-Fi communication module, connected to the STM32 over a serial interface (UART/SPI — to be decided during the concept phase) The operating environment is a construction machine: vibration, −40 °C to +85 °C, dust, moisture, and electrical disturbances from the vehicle harness (cranking, load dump, transients). The design must be built for these conditions from the start, not hardened afterwards. 2. Technical requirements 2.1 Power supply Input voltage range: 9–32 V DC continuous operation, covering both 12 V and 24 V vehicle systems Transient immunity per ISO 7637-2 (pulses 1, 2a, 2b, 3a, 3b) and ISO 16750-2 Reverse polarity protection Load dump immunity per ISO 16750-2 §4.6.4 Overcurrent and thermal protection Switching (buck) regulator designed with EMI in mind — layout optimised for low emissions Low-power mode (sleep / standby) with wake-on-CAN — target quiescent current to be agreed (goal: as low as practical, since the device may stay connected while the machine is off) Reference part for the main buck stage: ST A5975DTR — up to 3 A step-down switching regulator, 4–36 V input, 250 kHz fixed frequency, PowerSO-8, AEC-Q100 qualified, with a 10-year longevity commitment from ST. Please treat this as a reference and starting point, not a mandate. Two things we would specifically like your opinion on: The A5975D's 36 V absolute input ceiling leaves limited headroom above a 32 V rail once ISO 7637 transients and load dump are considered. We expect a protection front-end (TVS clamp, series element, or an active clamp / pre-regulator) ahead of it — please propose and justify your approach, or propose a higher-voltage part instead. At 250 kHz fixed frequency, please confirm the switching harmonics do not land badly relative to the CISPR 25 bands we need to pass, and design the input filter accordingly. If you believe a different regulator is the better engineering choice, say so in your proposal — a well-argued alternative is welcome. 2.2 CAN buses Two independent, galvanically isolated CAN buses (isolation at least at the transceiver level) CAN FD required, with backward compatibility to classic CAN 2.0A / 2.0B Bit rates: arbitration phase 125 kbit/s – 1 Mbit/s; CAN FD data phase up to 5 Mbit/s 120 Ω termination, software- or jumper-selectable — to be decided ESD / transient protection on CAN_H / CAN_L Target higher-layer protocols: J1939 and CANopen (firmware implementation is out of scope for this brief — what matters is that the hardware supports them) 2.3 Wireless Wi-Fi 2.4 GHz (802.11 b/g/n) on an ESP32 module — a pre-certified module preferred (e.g. ESP32-WROOM / WROVER or equivalent; final selection yours, with justification) Antenna: U.FL / IPEX connector for an external antenna, and optionally a footprint for a PCB/chip antenna — to be decided during the concept phase Properly engineered RF path: 50 Ω impedance matching, keep-outs, RF-appropriate stackup 2.4 Main microcontroller STM32 family — specific part selected and justified by you Requirements: at least 2 CAN FD controllers (FDCAN or equivalent), −40…+85 °C minimum (+105 °C grade preferred), good supply availability and long lifecycle (10 years minimum), package suitable for automated assembly SWD debug interface brought out to a connector or test pads Non-volatile storage for configuration and logs (EEPROM/FRAM or QSPI Flash) RTC with backup power (supercapacitor or battery — to be decided) 2.5 Inputs / outputs (to be confirmed in the concept phase) 4× isolated digital inputs, tolerant of vehicle supply voltage 2× analogue inputs, 0–10 V or 4–20 mA 2× high-side switch outputs with diagnostics and short-circuit protection Status LED indication ESD / transient protection on every line leaving the enclosure 2.6 PCB construction Multilayer (likely 4 or 6 layers — to be decided, given the RF and EMC requirements) Industrial or automotive grade components (AEC-Q100 / Q200 where available), −40…+85 °C minimum Designed for automated assembly (SMD; minimal THT) Conformal coating accounted for — masks and keep-outs defined Board dimensions and mounting points to be agreed. Target enclosure is an aluminium or plastic IP67 housing with Deutsch DT or AMP Superseal connectors. The enclosure and mechanical design are out of scope, but the PCB must be designed to fit them. 2.7 Compliance and EMC Certification testing is not part of this engagement, but the design must be built to pass first time: EMC: designed against the EMC Directive, ISO 13766 (earth-moving machinery), ISO 11452 and CISPR 25 Environmental: ISO 16750 (parts 1–5), IEC 60068-2 (vibration, shock, thermal cycling) RoHS / REACH compliant throughout Machinery Directive — the device is a sub-assembly installed in a machine 3. Scope of work (deliverables) Phase 1 — Concept and architecture Requirements review and clarification of open points Selection of key devices (STM32, Wi-Fi module, CAN transceivers, buck regulator, protection circuits) with justification and supply-availability analysis Block diagram, power budget, preliminary BOM cost estimate Proposed PCB stackup and estimated board dimensions Phase 2 — Schematic design Complete schematic in editable form (KiCad preferred; Altium Designer acceptable — please state which you use) Design calculations for critical sections (power, isolation, protection) Preliminary BOM with manufacturer part numbers, alternates (at least 2 sources for critical parts), and pricing at 100 / 1,000 units Schematic review with us before layout begins Phase 3 — PCB layout Placement, stackup, routing EMC/EMI-aware layout (ground partitioning, filtering, return paths, separation of power / CAN / RF sections) Properly implemented 50 Ω antenna path Thermal management (copper pours, thermal vias) Clean DRC against the chosen fabricator's rules DFM/DFA review and DFT provisions (test points for bed-of-nails or flying probe) Phase 4 — Manufacturing documentation Gerber X2 + drill files (or ODB++) Production BOM in a format ready for the assembly house Pick & Place (centroid) files, assembly drawings, top/bottom Assembly drawing with dimensions and mounting points 3D STEP model of the populated board — for enclosure integration Technical description / application note: pinout, connector definitions, supply parameters, start-up sequence, measurement points Bring-up test recommendations Phase 5 — Prototype support Support during prototype ordering (2–5 units) Bring-up and debug support for the first build Any resulting corrections rolled into revision B 4. Out of scope Firmware (STM32 and ESP32) — handled separately Enclosure and mechanical design Prototype fabrication and assembly EMC and environmental certification testing Wi-Fi side application / backend If you can cover these areas as well, please note it in your proposal — it is a plus, but not a requirement. 5. Requirements for the contractor Essential: Demonstrable experience in industrial or automotive electronics design (not consumer) Completed CAN / CAN FD projects — please give specific examples Experience with STM32 and with Wi-Fi/RF designs (RF layout, antenna matching) Practical design-for-EMC experience — designs that passed testing Proficiency in KiCad or Altium Designer Working communication in English or Polish Nice to have: J1939 / CANopen experience Projects for construction, agricultural, or commercial vehicle applications Experience taking designs into series production (not prototypes only) Hands-on familiarity with ISO 16750 / ISO 13766 6. Terms IP: full transfer of economic copyright in the design documentation to us upon final payment; source files (schematic, PCB, libraries) delivered in editable form Confidentiality: NDA signed before work begins Payment: per-phase, on acceptance of each deliverable Communication: weekly status update; video call at the schematic and layout review gates Contract: B2B (invoice) or contract for specific work with copyright transfer 7. What to include in your proposal Brief description of 2–3 comparable projects (what it was, your role, whether it reached production) Quote broken down by Phases 1–5 Proposed schedule (duration per phase) Which EDA tool you work in Any comments or objections to the assumptions above — particularly welcome if you think something in this spec is suboptimal Availability (start date, hours per week)

Skills required