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SentinelBus-DC
Data centre environmental monitoring over SNMP, powered directly from a 48–72V telecom bus rail.
- ESP32-S3
- W5500
- RS-485
- Modbus RTU
- SNMP
- Altium Designer
Problem
Data centre and telecom rooms need temperature, humidity, smoke and door/leak status delivered into existing NMS tooling — without adding a separate power supply or a proprietary dashboard.
System overview
A custom PCB that aggregates up to 32 distributed Modbus RTU sensor nodes over a galvanically isolated RS-485 bus spanning up to 1200 m, and exposes the aggregated data through a native SNMP v1/v2c agent on hardwired Ethernet. Four optoisolated dry-contact outputs and four isolated digital inputs interface directly with door contacts, leak detectors and UPS fault signals.
- 01Modbus RTU sensor nodes (≤32)
- 02Isolated RS-485 bus (≤1200 m)
- 03ESP32-S3
- 04W5500 Ethernet
- 05SNMP v1/v2c agent
- 06NMS (Zabbix / PRTG / Nagios)
Responsibilities
- Schematic capture and multi-layer PCB layout in Altium Designer
- Isolated power architecture and bus protection
- Firmware: Modbus RTU master, SNMP agent and custom MIB
- Bring-up, bench validation and NMS integration testing
Hardware architecture
- ESP32-S3 application processor
- Isolated DC-DC converter, 48–72V DC bus input
- Galvanically isolated RS-485 transceiver
- W5500 hardwired TCP/IP Ethernet PHY over SPI
- 4× optoisolated dry-contact outputs, 4× isolated digital inputs
Firmware architecture
- Modbus RTU master polling up to 32 sensor nodes
- SNMP v1/v2c agent with GET, TRAP and custom MIB support
- Compatible with Zabbix, PRTG and Nagios out of the box
- Developed in the Arduino IDE toolchain
Communication interfaces
- RS-485 / Modbus RTU
- Ethernet (SPI, W5500)
- SNMP v1/v2c
- Dry contact DI/DO
Engineering challenges
- Maintaining galvanic isolation across the RS-485 bus, digital I/O and the DC input while keeping the board compact
- Reliable signalling over a 1200 m bus with 32 nodes on a single segment
- Implementing a standards-compliant SNMP agent and MIB on a microcontroller rather than a Linux host
Hardware & diagrams
