🛠 Serveur web embarqué : l'Ethernet natif 10/100 du Teensy 4.1 (DP83825)

Objectives

The Teensy 4.1 integrates an Ethernet 10/100 Mbit controller with DMA and an on-board TI DP83825I PHY: only the RJ45 connector with magnetics is missing, sold as a solder kit. This tutorial sets up an HTTP server that exposes the board's measurements to the local network — no shield, no SPI, no chip-select.

Hardware

• 1 Teensy 4.1 (the TEENSY41_NE variant does NOT have an Ethernet chip: check your reference)
• 1 RJ45 connector kit: https://www.pjrc.com/store/ethernet_kit.html (fine soldering)
• Ethernet cable, DHCP router

Key points

• Since the PHY is internal, no Ethernet.init(cs) is needed: Ethernet.begin(mac) is sufficient.
• The official Ethernet library (WebServer, ChatServer, SMTP...) runs as-is on the 4.1.
• Ethernet.hardwareStatus detects the absence of hardware — essential to distinguish an NE variant from an unplugged cable.
• Ethernet.maintain renews the DHCP lease: call it in the loop.
• 10/100 only, no gigabit: for telemetry and lightweight APIs, this is more than enough.

Complete code

#include <Ethernet.h>

byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED }; // MAC unique !
EthernetServer server(80);

void setup {
  Serial.begin(9600);
  Ethernet.begin(mac);                    // DHCP ; (mac, ip) pour statique
  if (Ethernet.hardwareStatus == EthernetNoHardware) {
    Serial.println("Pas de materiel Ethernet (variant -NE ?)");
    while (true) delay(1);
  }
  server.begin;
  Serial.print("serveur a ");
  Serial.println(Ethernet.localIP);
}

void loop {
  Ethernet.maintain;
  EthernetClient client = server.available;
  if (!client) return;
  bool lineDone = false;
  while (client.connected && !lineDone) {
    if (client.available) {
      char c = client.read;
      if (c == '\n') lineDone = true;   // fin des en-tetes HTTP
    }
  }
  client.println("HTTP/1.1 200 OK");
  client.println("Content-Type: text/html");
  client.println("Connection: close");
  client.println;
  client.println("<html>A0 = ");
  client.print(analogRead(14));
  client.println("</html>");
  client.stop;
}

Expected verification

The IP address assigned by DHCP is displayed on the serial port; typing it into a browser displays a page showing the value of A0, refreshed on each reload.

Common errors

• Forgetting to solder the RJ45 kit (or accidentally buying the NE variant): hardwareStatus returns EthernetNoHardware.
• Cloning the example without changing the MAC address: two machines with the same MAC cause phantom network failures.
• Not calling Ethernet.maintain: the DHCP lease expires and the server becomes unreachable after a few hours.
• Alternatives if you don't have the kit: a W5500/Wiz820 shield on SPI works on all Teensy models — less elegant, but no soldering required.