Industrial Ethernet Temperature & Humidity Sensor – PCB & Hardware Design

Project Overview I am developing a professional/industrial Ethernet-connected temperature and humidity sensor with a local touchscreen display. The device will be installed as an environmental monitoring sensor and will communicate over Ethernet. It should be powered either from PoE Ethernet or an external 24VDC supply. I am looking for an experienced embedded hardware engineer who can design the complete electronics from schematic through production-ready PCB files. I have an existing Alibaba product that can be used as a general physical/functional reference: https://www.alibaba.com/product-detail/Remote-Web-Server-RJ45-Port-RS485_1601039957859.html The final device should be approximately similar in size/form factor, but the hardware should be properly engineered for our requirements rather than simply copied. Main Product Requirements The product is an Ethernet temperature and humidity sensor. It should provide: Temperature measurement Relative humidity measurement 10/100 Ethernet PoE power 24VDC power input Local touchscreen display Embedded processor Ethernet-based configuration and communication There are no RS-485 requirements. There are currently no additional analog or digital I/O requirements. Power The PCB must support both: 1. PoE The device will operate as a PoE-powered device (PD) receiving power from a standard PoE Ethernet switch. 2. 24VDC The device must also accept an external 24VDC power supply. The engineer should design the appropriate power architecture so the product can safely operate from either source. The design should include appropriate: PoE circuitry DC/DC conversion Voltage regulation Input protection Reverse-polarity protection where appropriate Overvoltage/transient protection ESD protection Power-source management Thermal considerations The engineer should explain the proposed power architecture. Temperature & Humidity Sensor The temperature and humidity sensing system is a critical part of the project. The engineer should recommend an appropriate sensor based on: Temperature accuracy Humidity accuracy Long-term stability Operating range Response time Availability Production cost Long-term availability Industrial suitability Possible sensor families may include Sensirion, Bosch, TI, or equivalent devices, but I am open to recommendations. Important thermal consideration The PCB must be designed so that heat generated by: Processor PoE circuitry DC/DC converters Voltage regulators Ethernet PHY Display does not significantly affect the temperature measurement. The engineer should recommend the appropriate sensor location and PCB/layout strategy to minimize self-heating and measurement error. If necessary, the sensor should be physically separated from heat-generating components or placed in an appropriate location within the enclosure. This is an important requirement. Processor The processor has not yet been selected. I want the engineer to recommend the best architecture for this product. Possible approaches include: ESP32-class processor STM32-class MCU Linux-capable processor/SoC Other suitable embedded processor I am open to the engineer's recommendation. The engineer should compare the options based on: Processing requirements Ethernet support RAM/Flash Touchscreen interface Web server requirements SNMP BACnet Modbus TCP/IP Power consumption Cost Availability Long-term product lifecycle Production suitability I will develop the firmware/software. The firmware will provide: Web server SNMP BACnet Modbus TCP/IP Sensor data acquisition Local display functionality The hardware engineer does not need to develop this software. Touchscreen The device should have an integrated touchscreen. Target display size: 3.5" or 4.3" The engineer should recommend the most appropriate display. The display should be evaluated based on: Size Resolution Touch technology Interface Processor compatibility Availability Cost Power consumption Industrial suitability Long-term availability The engineer should propose at least one primary display and suitable alternatives. Ethernet Requirements: 10/100 Mbps Ethernet RJ45 connector PoE Ethernet PHY and magnetics ESD protection Appropriate EMC/EMI design The Ethernet section should be designed according to good industrial PCB design practices. CE / EMC The product is intended for eventual commercial production. The hardware should therefore be designed from the beginning with CE and EMC compliance in mind. The engineer should consider: ESD EFT/transients Surge protection Conducted emissions Radiated emissions Grounding Shielding Ethernet protection PoE protection Power supply filtering PCB stack-up Component placement Return paths Enclosure considerations The engineer should identify the relevant standards and design considerations for this type of product. Previous experience designing products that successfully passed EMC/CE testing is highly preferred. PCB The PCB should be designed for eventual production. Required design considerations include: Appropriate PCB stack-up Controlled/high-speed Ethernet routing where required Good analog/sensor layout practices Thermal management EMC/EMI DFM/DFA Component availability Manufacturing tolerances Testability Production assembly The board should be approximately similar in size to the reference product. Deliverables The freelancer must provide: Complete schematic Complete PCB layout Editable/source PCB design files Gerber files BOM CPL / Pick-and-Place files Component manufacturer part numbers Component alternatives PCB stack-up recommendation 3D model if supported Component/library source files required to reproduce the design Manufacturing documentation Hardware design documentation All source design files must be delivered at project completion. Ideal Engineer I am looking for an experienced embedded hardware engineer, not only a PCB layout technician. Strong experience in the following areas is preferred: Industrial sensors Temperature/humidity measurement PoE Ethernet Embedded processors ESP32 STM32 Embedded Linux Touchscreens Power electronics EMC/EMI CE certification Production PCB design DFM/DFA Experience with commercial/industrial products that have gone into production is highly preferred. Important Technical Question In your proposal, please tell me: Which processor would you recommend and why? Would you choose ESP32, STM32, Linux, or another architecture? Which temperature/humidity sensor would you recommend? How would you prevent PCB/PoE/processor heat from affecting the temperature measurement? Which 3.5" or 4.3" touchscreen would you recommend? How would you implement PoE + 24VDC power? What would you do to make the design more likely to pass CE/EMC testing? Please provide examples of similar production hardware you have designed. Final Product The target product is essentially a compact industrial environmental sensor: Temperature + Humidity Sensor → Embedded Processor → Ethernet → SNMP / BACnet / Modbus TCP/IP / Web Server with: PoE or 24VDC → Power Management → Electronics and a: 3.5"–4.3" Touchscreen → Local Temperature/Humidity Display & Configuration The goal is to create a professional hardware platform suitable for prototype production initially and eventual commercial production.