Amateur radio and embedded systems

Connecting Modbus RTU to TCP with Waveshare RS485 to Ethernet converter

I have been planning to connect my Modbus electricity meter to Home Assistant for a while. Unfortunately my Home Assistant machine is placed far away from the breaker panel and I wanted to avoid running extra cabling. Modbus RTU to Modbus TCP conversion has been a solved problem for a long time. However, most of the converted boxes are designed for use in the industrial sector so they tend to be quite expensive and large. I also wanted to use Wi-Fi instead of wired Ethernet which would make the converted even more expensive. Fortunately I found the Waveshare RS-485 to Wi-Fi and Ethernet converter. It was pretty cheap on Aliexpress so I gave it a try.

The converter supports all kinds of protocols like Modbus, raw serial, MQTT, some HTTP services etc. It can connect to Wi-Fi and wired Ethernet. Setting it up is pretty easy. It starts up as a wireless access point by default so I did not even have to dig out an Ethernet cable. There is a (pretty crude) web interface where I only had to set the main mode (Modbus TCP server), RS-485 settings (baud & parity) and the wireless network to connect to.

Does it work? YES! After the initial configuration and wiring I did not have to touch anything. It speaks standard Modbus TCP (on a non-standard port though) and works well with mbpoll and Home Assistant. I power it from a Mean Well DIN rail power supply. It has been running trouble free for weeks at 9600 baud with short (below 50 cm) wiring and no RS-485 termination. No hangs. No lost communication. As trouble-free as you can imagine.

I can definitely recommend this converter for home use.

Let's see what is inside...


The front has some standard LED indicators. They blink during Modbus RTU communication. The enclosure fits a DIN rail however the front surface is larger than a standard circuit breaker so you may have to make a bigger cut out in the panel to fit the converter.

Front view


The top side has an SMA antenna connector, Ethernet socket and the RS-485 terminal block. The terminal block is pluggable so you can prepare the cabling before mounting the converter. SMA is a less-standard choice for Wi-Fi (RP-SMA is the usual choice) so watch out if you plan to replace the stock antenna.

Side-top view


The bottom side has only the power supply terminal block (also pluggable).

Side-bottom view

PCB top

The device is built from two PCBs connected at right angle. On the bigger PCB there is a Wi-Fi module and... that is basically it. Only some LEDs, connectors and through-hole components stick out.

PCB top view

PCB bottom

There are more things happening on the bottom. You can see the power supply inductors on the left side and some small discretes. I could not find the Ethernet PHY. It may be part of the module on the other side. Overall assembly & soldering quality looks pretty good. PCB bottom view

Back PCB

The smaller back PCB has the screw terminal block connectors, RS-485 transceiver, some protection components (probably a varistor) and some unpopulated footprints. PCB side view