Serial-to-Ethernet and Cellular DTU Adaptation | Obeita
This configuration is proposed for assessment. Confirm interfaces, components and performance for your specific project.
Use one compact ESP32-S3 DTU design where some installations have Ethernet, others have Wi-Fi, and remote locations need cellular access. The core task is to carry RS485 device data to a configured IP endpoint, with the uplink and firmware framework selected for the deployment.
Three distinct uplink implementations
W5500 connects over SPI and supplies a hardware TCP/IP path. The ML307R Cat.1 modem is controlled through AT commands, while Wi-Fi uses the ESP32-S3 radio. TCP, UDP, HTTP and MQTT can be selected as integration protocols; automatic switching between these links is an additional policy that must define priority, timeout and recovery.
Power and field wiring
The design offers USB 5 V for development and a 12–24 V DC input using TPS54331 conversion. Cellular start-up and transmit peaks need a power-budget check. The RS485 connector carries A, B, ground and a field supply connection, with TVS protection and jumper-selectable 120-ohm termination. Terminal voltage must be checked for the actual supply arrangement before powering a sensor.
Firmware and modem bring-up
ESP-IDF, Arduino and MicroPython are possible development routes, chosen according to library support and maintenance requirements. CH340C and an automatic download circuit provide programming access. ML307R UART signalling must be checked against the MCU voltage domain: correct modem power does not make a 1.8 V serial interface directly compatible with 3.3 V logic.
Proposed design configuration
These are configuration inputs for development; the final assembly, firmware and acceptance tests define the delivered specification.
| Item | Configuration |
|---|---|
| Controller | ESP32-S3 |
| Ethernet | W5500 over SPI; RJ45 |
| Cellular option | ML307R Cat.1; region/carrier compatibility review |
| RS485 | TVS; selectable 120 Ω termination |
| Programming | USB / CH340C / automatic download |
| Power paths | USB 5 V or 12–24 V DC design |
Project questions
Does selecting three uplinks provide automatic failover?
No. Link availability and automatic failover are different. We define when to switch, how to restore sessions and what happens to unsent data.
Can the RS485 port power an external instrument?
Only after checking the connector assignment, available voltage and current, and grounding. Do not infer sensor power from the DTU input rating.
Plan this project
Send sample RS485 frames, the destination IP/API, installation country and power arrangement to define the DTU connection path.