求助：Arduino Uno搭配W5100以太网盾DHCP配置失败
Hey there, let's work through this DHCP issue you're facing with your Arduino Uno and W5100 Ethernet shield. I've helped folks debug this exact problem before, so let's break down the most common fixes step by step:
1. Double-Check Hardware Connections
- Make sure the Ethernet shield is firmly seated on top of your Arduino Uno—sometimes a loose connection can break communication between the board and shield.
- Verify your Ethernet cable is functional: swap it with the one your laptop uses, or plug it into a different port on your router to rule out a faulty cable/port.
- Confirm the W5100's Chip Select (CS) pin is set correctly. The default is pin 10, but if you’ve modified your setup or have other components using this pin, explicitly define it in code like this:
Ethernet.begin(mac, 10); // Explicitly set CS pin to 10
2. Use a Unique MAC Address
The default MAC address in the DhcpAddressPrinter example (0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED) is shared by thousands of beginners, which can cause conflicts on your network. Tweak it to a unique value—just change the last 1-2 bytes, for example:
byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xEE };
3. Verify Router DHCP Settings
Even though your laptop connects fine, there are a few router settings to check:
- Ensure MAC address filtering is disabled (or add your Arduino's new MAC address to the allowed list if it’s enabled).
- Check if your router’s DHCP address pool is full. Log into your router’s admin panel and look at connected devices—if there are no available IPs left, expand the pool or disconnect some devices temporarily.
4. Extend DHCP Timeout
Sometimes the default 5-second DHCP timeout isn’t enough for slow network handshakes. Add this line right before Ethernet.begin(mac) to give it more time:
Ethernet.setTimeout(10000); // Set timeout to 10 seconds
5. Rule Out Power Issues
W5100 shields can draw more power than a low-power USB port can provide. Try these fixes:
- Use a powered USB hub to supply power to your Arduino.
- Switch to an external 9V/1A power supply instead of relying on USB power.
Give these steps a try one by one—most of the time, it’s either a loose connection, duplicate MAC address, or power issue causing the DHCP failure.
内容的提问来源于stack exchange，提问作者Kim Carlo
