Dual CAN STM32 ESP32 Gateway

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)