Rugged 40A Industrial/Automotive Time-Delay Relay (Fixed Price)

### Project Overview We are looking for an experienced embedded hardware engineer to design a rugged, dual-voltage (12VDC/24VDC) cyclic time-delay relay. The device will be bundled as an accessory for industrial, forestry, agricultural, and mining equipment operating across North America and Europe. While maintaining a target unit manufacturing cost (COGS) of ~$3.70 USD (~$5.00 CAD) at 1,000-unit production volumes is important, field reliability is paramount. The device will operate in harsh engine bays exposed to severe vibration, thermal shock, dust, fuel/solvents, and power washing. We need a designer who understands how to select high-quality domestic Chinese components, implement robust high-current PCB tracing, and build a rock-solid industrial circuit that will not freeze, corrupt, or fail under harsh electrical noise. --- ### Key Technical Specifications 1. Control Logic & Interface: - Functionality: Repeating loop timer (~15 seconds ON / ~20 minutes OFF). High timing precision is NOT required. - 4-Wire External Harness Interface: V+ (12VDC/24VDC operational input), GND, Switched LOAD output, and a dedicated "ON NOW" trigger line that resets the timing cycle upon a momentary button press/ground pulse. 2. Form Factor, Pin Mapping & Internal Ground Routing: - Physical Case: Standard ISO Mini Relay plastic cube enclosure (~28mm x 28mm / 1-inch cube) specified in high-temp, UV-resistant PBT or PA66 plastic. - Terminal Interface: Standard 5-blade 6.3mm (1/4") male spade terminals on the baseplate. - Pin Mapping & Internal Ground Tie (Form C Layout): * Pin 30 = Line V+ Input * Pin 87 = Switched LOAD Output (Normally Open) * Pin 85 = Ground (GND) * Pin 86 = External "ON NOW" Trigger Wire * Pin 87a = Tied directly to GND (Pin 85) internally on the PCB to allow the motor ground return lead to connect straight into the relay socket for a simplified harness. 3. Load Switching Stage, High-Current Tracing & Inductive Protection: - Internal Assembly: Heavy-duty 40A open-frame/PCB-mount mechanical relay core integrated onto the PCBA. - Ratings: Rated for 40A switching performance at 12VDC/24VDC. Switches line voltage directly to the load via the relay contacts. - High-Current Copper Tracing (V+, 87, and 87a): The high-current power paths—including V+ to Pin 30, Pin 87 to Load, and Pin 87a to Pin 85 (GND)—must use heavy copper layout (2 oz or 3 oz) with wide trace pours and heavy via stitching to comfortably pass up to 40A continuous without thermal buildup. - Ground Isolation: High-current motor return ground on Pin 87a must be laid out to prevent ground-bounce noise from interfering with the MCU logic ground. - Inductive Load Protection: The relay will switch a small compressor motor on and off. The output circuit must include proper snubber / flyback diode protection to suppress inductive kickback and prevent contact pitting/welding. 4. Power Protection & Reverse Polarity: - Reverse Polarity Protection: Dedicated reverse polarity protection (e.g., low-drop P-channel MOSFET or high-current Schottky/diode protection) on the V+/GND lines so reverse wiring will not damage the module. - Transient Protection: Dedicated logic power supply stage (12V/24V down to 3.3V/5V) with heavy-duty TVS diode array to comfortably survive ISO 7637-2 / ISO 16750-2 load dump surges common in 24VDC heavy machinery. 5. Compliance & Environmental Requirements: - CE Certification Readiness: Designed to pass European CE compliance testing (EMC/EMI compliance per EN 61000 / EN 55032 standards, including ESD protection on all input lines). - MCU & Hardware Safety: Must use a proven, reliable Tier-1 MCU family (e.g., ATtiny, STM8, or high-tier WCH) with Hardware Watchdog Timer (WDT) and Brown-Out Detection (BOD) enabled. - Sealing / Environmental: Designed for full polyurethane or epoxy potting at the baseplate to achieve IP67 waterproof/dustproof protection and mechanical vibration resistance. 6. Production & Turn-Key Manufacturing Handoff: - The design must be optimized for automated, turn-key production through Chinese PCBA contract manufacturers (e.g., JLCPCB, PCBWay, or similar turn-key assemblers). - The manufacturer must be capable of a complete "box-build" process: fabrication, SMT placement, automated firmware programming, inserting the assembly into the ISO Mini housing, applying bottom potting compound, and bulk-packaging the finished units in trays/cartons for bulk shipping. - The freelancer will prepare all factory-ready manufacturing packages (BOM, Gerber, CPL/PNP, assembly drawings, firmware flashing files) and coordinate directly with the manufacturer during the prototype run to validate bulk production under the ~$3.70 USD target COGS. --- ### Required Deliverables 1. Native Schematics & PCB Layout (Altium or KiCad) + Gerber and Pick-and-Place (CPL) files formatted for turn-key SMT manufacturing. 2. CE Compliance Pre-Compliance Checklist / Design Considerations Document. 3. Optimized BOM targeting ~$3.70 USD (~$5.00 CAD) COGS at 1,000 units utilizing in-stock, high-quality Chinese domestic components. 4. Fully commented firmware source code/binaries + factory production flashing package. 5. 3D CAD/STEP file showing board, 40A bare relay, housing, and potting assembly. 6. Turn-key manufacturing setup package verified with a PCBA assembler (validating automated PCB build, firmware flashing, housing assembly, potting, and bulk tray packaging). 7. Delivery of 5 fully assembled, potted, and working prototypes for validation. --- ### Expected Milestone Structure This project will be executed as a fixed-price contract structured across the following milestones: - Milestone 1 (20%): Schematics, Component Selection, Reverse Protection & CE Review - Milestone 2 (30%): PCB Layout, 40A Copper Routing, Thermal Design & 3D CAD - Milestone 3 (20%): Firmware Code & Turn-Key Factory Handoff Package - Milestone 4 (30%): Physical Prototype Delivery, Load Validation & Bulk Readiness ### Preferred Qualifications - Strong background in high-current PCB layout, motor load snubbing, and automotive transient suppression. - Direct experience coordinating with Chinese turn-key SMT assemblers (JLCPCB, PCBWay, etc.). - Familiarity with CE marking requirements for automotive/industrial electronics. All intellectual property rights will belong 100% to us upon payment. If you meet these qualifications, please apply with examples of similar power electronics or automotive PCB projects you have designed!