1. What Is Wi-Fi?

Wi-Fi is a wireless LAN technology that connects devices to an IP network without pulling cable. It is defined by the IEEE 802.11 family of standards and, in the 2.4 GHz band, works on channels that are 20 MHz wide, where only 1, 6 and 11 avoid overlapping each other. The 5 GHz band adds many more channels and wider 40 MHz and 80 MHz options. Because Wi-Fi is IP-native, everything that runs over Ethernet - HTTP, TCP, UDP, MQTT, Modbus TCP - runs over Wi-Fi without a protocol translation layer.

Core characteristics:

  • IP-native transport: the module is a full network peer, so cloud platforms, brokers and OTA update servers can talk to it directly.
  • Band and channel based: real performance depends on band, channel width, congestion and antenna gain rather than on a single data-rate number on a datasheet.
  • Security by design: WPA2-PSK and WPA3 with AES encryption are mandatory in practice, unlike a bare serial bus that carries plain bytes.
  • Flexible topology: a star around one access point, a mesh with several access points, or a self-forming network for multi-hop coverage.
  • Shared airtime: every client on the same channel competes for the medium, which is the root cause of most latency complaints in the field.

2. How Does Wi-Fi Work?

A Wi-Fi station does not simply transmit. It first has to join a network and obtain an IP address. In practice the sequence looks like this:

  1. Scanning and association: the module scans for beacons, selects an SSID and associates with the access point.
  2. Authentication and key exchange: with WPA2-PSK or WPA3, the station and the access point run a handshake and derive session keys. Wrong credentials fail here, long before your application code runs.
  3. IP configuration: the module obtains an address by DHCP or uses static IP, gateway and DNS settings configured on the device.
  4. Data exchange: the link layer uses carrier sensing with acknowledgement and retries, while TCP, MQTT or HTTP run on top of it.
  5. Keep-alive and roaming: periodic keep-alive traffic holds NAT sessions open, and the module can move between access points in a mesh deployment.

Steps one to three are where most field failures actually happen, because they depend on credentials, signal level and DHCP behaviour rather than on your firmware logic.

3. What Is RS485?

RS485 is a bidirectional, half-duplex serial bus for industrial data exchange, standardized as TIA/EIA-485. It defines the electrical layer - differential signalling over a twisted pair, normally labelled A and B - so that endpoints agree on voltage levels and common-mode tolerance, while the message format is defined above it, most often by Modbus RTU. In daily engineering work the two names are used almost interchangeably, because an RS485 port without a protocol running on top of it is rarely useful.

Core characteristics:

  • Differential transmission: the receiver reads the voltage difference between the two lines, so common-mode noise on a factory floor is largely rejected before it reaches the UART.
  • Multi-drop bus: up to 32 standard unit loads per segment, with 120 ohm termination at both ends of the trunk and short stubs.
  • Long reach: roughly 1200 m per segment at low baud rates on twisted pair, with distance trading off against baud rate.
  • Half-duplex and normally polled: one talker at a time, so a master-slave loop keeps traffic deterministic and easy to debug with a serial analyser.
  • Low cost, no stack: a transceiver needs no IP address, no DHCP lease, no security handshake and no firmware update policy.

4. Wi-Fi vs RS485: What Is the Difference?

Wi-Fi and RS485 turn up in the same system far more often than they compete with each other - a Wi-Fi gateway on one side, an RS485 or Modbus trunk on the other. They differ in what they are good at:

Dimension Wi-Fi RS485
Working mode Carrier-sense multiple access with collision avoidance on a shared channel; every node is an IP peer inside a star or mesh topology Half-duplex differential bus, normally master-slave polling, with only one node transmitting at any moment
Speed and performance Practical link rates of tens of Mbps, shared among all clients on the access point; per-packet jitter grows with congestion 9600 to 115200 bps typical, with short frames and low jitter inside a polled loop; distance limits the usable baud rate
Distance Tens of metres indoors, and several hundred metres outdoors with directional or high-gain antennas and line of sight Up to about 1200 m per segment at low baud rates, extendable with repeaters
Topology and node count Star around an access point, typically a few dozen clients, or a mesh with multiple access points Multi-drop trunk, up to 32 unit loads per segment
Noise immunity and security Shared medium and open air, so it relies on channel planning, retries and WPA2 or WPA3 encryption Differential signalling over twisted pair gives strong common-mode rejection, but the data itself is unencrypted
Typical application Cloud connectivity, cameras, HMI panels, remote configuration, mobile equipment PLCs, energy meters, sensors, motor drives, on-machine wiring inside a cabinet or plant

The practical reading of that table is that the two technologies are complementary rather than competing. RS485 collects data from the devices that live on the bus, and Wi-Fi carries the data to the network.

5. Common Configuration and Key Parameters

A serial-to-Wi-Fi module has two sides, and both must be configured before the link behaves reliably.

RF and network side

  • SSID and security mode: the exact SSID, which is case-sensitive, together with WPA2-PSK or WPA3 and the pre-shared key. Hidden SSIDs must be set explicitly on the module.
  • Band and channel: 2.4 GHz is preferred for coverage and for modules with PCB antennas; in dense installations pin the access point to channel 1, 6 or 11 instead of leaving it on auto.
  • Transmit power: configured in dBm, for example 18 to 20 dBm on a typical 2.4 GHz module, and always within local regulatory limits. More power is not automatically better on a short link.
  • IP configuration: DHCP or a static address, plus gateway and DNS. A static address is standard practice in industrial cabinets where the network plan is fixed.
  • TCP, UDP or MQTT parameters: remote host, port, client ID, keep-alive interval and reconnect policy.

Serial side, between module and MCU or RS485 transceiver

  • Baud rate: 9600, 19200, 38400 or 115200 bps are the common settings, and both ends must match exactly.
  • Data bits, parity and stop bits: 8-N-1 is the default for almost every Modbus RTU device, so confirm the meter or PLC manual before changing it.
  • Flow control: usually none. On RS485 the direction control line must switch the transceiver quickly enough that the first and the last byte of each frame are not clipped.
  • Frame gap: Modbus RTU uses a silent interval to delimit frames, so a module that buffers or splits serial data can break frame timing. Prefer a module that forwards serial data transparently.

6. When Wi-Fi Fits and When It Does Not

Good fit

  • Devices that must reach a cloud platform, an MQTT broker or an ERP system without new cabling.
  • Nodes with mains power or a generous battery budget, sending bursty rather than continuous traffic.
  • Sites where installing cable is expensive or physically impossible, such as retrofits, temporary test rigs and mobile equipment.
  • Areas that benefit from mesh coverage, where several access points or a self-forming mesh have to cover a large floor.

Poor fit

  • Hard real-time, deterministic control loops, because airtime is shared and retries make jitter unpredictable.
  • Multi-year battery sensors in the field, where the radio and the IP stack keep average current far above what LoRa or NB-IoT achieve.
  • Harsh electromagnetic environments such as welding areas or variable-frequency drive cabinets, where a differential wired bus is inherently more forgiving.
  • Very dense deployments, where dozens of clients streaming on one access point degrade throughput for everyone.
  • Safety-critical interlocks, where a wired loop remains the responsible engineering choice.

7. Real-World Applications in Industrial and IoT Systems

In industrial automation, building management and energy monitoring, the most common pattern is a Wi-Fi gateway sitting in front of an RS485 trunk. The gateway polls the Modbus RTU registers and then publishes them over MQTT or HTTP, so the existing PLC, meter or sensor keeps its wiring and gains remote visibility. Nothing on the bus has to change, which is exactly why this approach is so widely deployed.

Ebyte module families map onto that pattern directly. The E103-W03, built on the TI CC3220R, is a serial-to-Wi-Fi module with AT command support and MQTT in a small SMD footprint, which suits designs where the RS485 transceiver already sits on the board and only the wireless side has to be added. When coverage is the constraint rather than cost, the E103-W07 supports mesh networking with up to 1000 nodes, so a single gateway can cover a floor through several self-forming hops. The E103-W02 (TI CC3200, 2.4 GHz, 20 dBm) and the low-power E103-W08B, which handles TCP, HTTP client and MQTT traffic through an IPEX antenna, sit at the two ends of the trade-off between link budget and average current consumption. On the bus side, RS485 DTU products such as the E95-DTU(433L20-485) pair an RS485 and Modbus port with a long-range radio link, which is the pragmatic answer for cabinets where Wi-Fi coverage cannot be guaranteed.

The selection logic stays simple: choose the bus for the devices, choose the radio for the distance to the network, and keep the interface between them transparent.

8. FAQ: Common Problems and Field Troubleshooting

Q1: Will Wi-Fi replace RS485 in industrial systems?

No. Wi-Fi has replaced the uplink, not the bus. RS485 remains the cheapest and most deterministic way to talk to a dozen devices inside a cabinet, and most industrial Wi-Fi deployments are gateways that bridge an existing RS485 or Modbus trunk rather than replace it. The two technologies sit at different layers: the bus handles device-level polling, and Wi-Fi handles the IP uplink.

Q2: How do I connect an existing RS485 or Modbus RTU device to Wi-Fi?

  • Confirm the serial parameters of the device first: baud rate, data bits, parity, stop bits and its slave address.
  • Use a serial-to-Wi-Fi module or gateway that forwards serial data transparently, and set identical parameters on the serial side.
  • Decide the application-layer mapping: Modbus RTU to Modbus TCP, or poll Modbus RTU locally and publish the values as MQTT topics. The second option is far more robust over a wireless link.
  • Test with a Modbus polling tool before touching the cloud side. If the register read fails locally, it will fail remotely as well.

Q3: The module associates with the access point but the TCP or MQTT connection drops repeatedly. Where do I start?

  • Check RSSI and channel congestion: a link that sits below roughly -75 dBm will disconnect whenever the environment changes. Move the antenna, raise the module, or change the access point channel.
  • Check the keep-alive interval: many NAT routers and firewalls silently drop idle TCP sessions, so a keep-alive shorter than the NAT timeout keeps the socket alive.
  • Check DHCP lease and client limits: a client that reconnects every time the lease expires usually has a static IP misconfiguration.
  • Check the power supply: Wi-Fi modules draw current in short bursts, and an undersized regulator causes resets that look exactly like network failures.

Q4: Data from the RS485 side arrives garbled, or the module receives nothing at all. What should I verify?

  • Baud rate mismatch is the single most common cause of garbled frames, so verify it on both sides rather than trusting the configuration file.
  • A and B line reversal is a classic first-installation error, and it produces silence rather than noise.
  • Termination and stub length: 120 ohm at both ends of the trunk, with stubs kept short. Missing termination usually shows up as errors only at higher baud rates.
  • Direction-control timing: if the transceiver switches late, the last byte of each response is truncated, which looks like an intermittent protocol error.
  • Frame timing: a module that buffers serial data can break the Modbus RTU inter-frame gap. Enable transparent forwarding or increase the device timeout.

Q5: How many RS485 nodes can I poll through one Wi-Fi gateway, and what latency should I expect?

The bus is normally the constraint: up to 32 unit loads per segment, and each poll costs the frame time at your baud rate plus the response time of the device. At 9600 bps a short poll-and-response pair takes tens of milliseconds, so a dozen nodes can be scanned in well under a second. Beyond that, poll fewer registers per cycle or split the trunk into segments, because the Wi-Fi uplink is rarely the bottleneck in a polled Modbus system.