UNO R3 + W5100 channel messaging

Use an UNO R3, W5100 Ethernet shield, LED with a 330 Ω series resistor (220–560 Ω is suitable), button, and breadboard. The LED output is D3; connect the button between D2 and ground. The input uses INPUT_PULLUP, so pressing reads LOW. W5100 uses chip select D10.

Install IOSignal, its dependencies, and Bounce2. Open the library's uno_ethernet_channel_txrx example. Give each Ethernet board a unique MAC address and connect it to a router providing DHCP. The example uses Serial at 115200 baud, an 80-byte receive buffer, and io.iosignal.net:55488.

The program calls io.loop() on every loop iteration and debounces the button with Bounce2 (5 ms). Once ready, it subscribes to #homeButton. A button press sends #homeButton with text uno3-eth. Receiving this tag toggles the LED; the text identifies the sender and is not an on/off command.

Open the workbench, connect to wss://io.iosignal.net/ws, and use the basic channel preset. The browser and board must use the same server and home-channel network group. Send #homeButton to toggle the LED; press the physical button to see its message in RX. A browser echo alone does not prove the board received the message.

For DHCP failures, check Ethernet cabling and MAC uniqueness. For a ready connection with no LED response, check server, channel spelling, network group, and polarity. If using a local server, configure the board with the computer's LAN IP and TCP port, not localhost. See connection environments.