1. Ethernet PHY: Use an Ethernet PHY chip that supports the IEEE 802.3 standard. A common choice is the LAN8720, which is often used with ESP32 for Ethernet capability.
2. Modbus Protocol: Modbus is a communication protocol that can run over various types of network media, including Ethernet. Implementing Modbus may require a software library depending on whether you want Modbus TCP/IP, RTU over Ethernet, etc.
3. RJ45 Connector: You will need an Ethernet jack with integrated magnetics or discrete magnetics to interface with the Ethernet PHY.

1. ESP32 to Ethernet PHY:
   • Connect the ESP32's RMII-related pins (such as IO0, IO19, IO21, etc.) to the respective pins on the Ethernet PHY chip according to the RMII interface.
2. Ethernet PHY to RJ45:
   • Use capacitive coupling from the PHY's transmit and receive lines to the RJ45 jack.
   • Connect the magnetics (if discrete) in series between the PHY and the RJ45 connector.
3. Power Supply:
   • Make sure your setup is powered correctly. The ESP32 operates at 3.3V, so ensure your PHY and any associated components are compatible with this or that you have necessary level shifting.
4. Grounding:
   • Grounding should be consistent and stable between your components, especially the PHY and the RJ45 connector.

1. Software:
   • Implement or use an existing Modbus library for ESP32 if you plan to use Modbus over this setup. Libraries such as "Modbus-Master-Slave-for-ESP8266" might work for your case with some modifications for ESP32.
2. Testing:
   • Verify your connections and configuration using simple PING tests for Ethernet, followed by library-based tests for Modbus communication.

1. Ethernet PHY: LAN8720 is a popular choice for connecting with ESP32.
2. RJ45 Connector: Choose a connector that either has integrated magnetics or plan to use external magnetics.
3. Capacitors: Typically used for DC blocking on the transmission lines.
4. Resistors and Crystals: Required for PHY configuration and clock generation.

• Power Pins:
  • Connect LAN8720 VCC and all necessary power pins to a 3.3V supply.
• RMII Interface:
  • IO0 (CLKETH): Connect to LAN8720's XTAL1 if used as the clock input.
  • IO17 (CRS_DV): Connect to CRS_DV on the LAN8720.
  • IO19 (TXD0): Connect to TXD0 on the LAN8720.
  • IO22 (TX_EN): Connect to TX_EN on the LAN8720.
  • IO25 (RXD0): Connect to RXD0 on the LAN8720.
  • IO26 (RXD1): Connect to RXD1 on the LAN8720.
  • IO27 (MDC): Connect to MDC on the LAN8720.
  • IO23 (MDIO): Connect to MDIO on the LAN8720.

• Use capacitors between the TX+/TX- and RX+/RX- lines of the LAN8720 and the RJ45 connector.
• Ensure magnetics are correctly placed either internally within the RJ45 or using external transformers.

• Add a 50 MHz oscillator if the LAN8720 requires it (if the clock signal isn't being provided from your ESP32).
• Use pull-up/pull-down resistors as needed, especially on the PHY reset pin or any configuration pins.

• Use the ESP32 IDF or Arduino library that supports Ethernet.
• For Modbus, consider libraries such as Modbus-Master-Slave-for-ESP8266 as a starting point and adapt them for Ethernet/ESP32 if necessary.

• Ensure all power and ground connections are stable.
• Start with verifying the LAN8720 can achieve link status (control LEDs on the RJ45 if available).
• Test PING from the ESP32 to confirm basic Ethernet functionality.

graph TD;
    ESP32([ESP32-WROOM-32D])
    LAN8720[LAN8720 Ethernet PHY]
    RJ45[RJ45 Connector]

    ESP32 ---|RMII Interface| LAN8720
    LAN8720 ---|TX+/TX-, RX+/RX-| RJ45
    ESP32 -->|Power| LAN8720
    RJ45 <--> |"Capacitors & Magnetics"| LAN8720

• Connect RMII Pins: From the ESP32 to the appropriate pins on the LAN8720 PHY.
• Connect LAN8720 to RJ45: Using capacitors and either integrated or external magnetics.
• Add Power Connections: Ensure 3.3V power is provided to both the ESP32 and the LAN8720.

1. Crystals and Oscillators:
   • 50 MHz Oscillator: Necessary for the LAN8720 clock.
   • Some setups can use the ESP32's internal clock to provide this, reducing the need for an external oscillator.
2. Resistors and Capacitors:
   • Pull-up/down Resistors: Often used on reset or configuration pins. Typical values are 4.7kΩ to 10kΩ.
   • Decoupling Capacitors: Place these near the power pins of both the ESP32 and LAN8720 for stability, using values like 0.1µF.
3. RJ45 with Integrated Magnetics (recommended if space permits):
   • Reduces the complexity of layout and ensures better signal integrity.

1. Ethernet Library: Use the ESP-IDF framework if you’re familiar with it, as it supports Ethernet out of the box. If using Arduino, libraries like ETH.h provide Ethernet support.
2. Modbus Library:
   • For using Modbus/TCP, there are various libraries available like the ArduinoModbus library. You may need to adapt some parts for ESP32 compatibility.

1. Create the Schematic:
   • Start connecting components in Flux as per the provided guidelines. Begin with key connections like the RMII interface.
2. Layout the PCB:
   • Pay attention to differential pair routing for TX/RX lines, keeping them length-matched and minimizing crosstalk.
3. Simulate Your Circuit (if possible):
   • While Flux might not support full simulation for this setup, verification of connections before finalizing your PCB is crucial.

• Review your design for any errors, especially power and ground connections.
• Order a prototype PCB for testing.
• Load firmware to test Ethernet connectivity (basic PING) before integrating Modbus.

1. Ethernet PHY: LAN8720
   • Connects to the ESP32 via the RMII interface.
2. RJ45 Connector with Integrated Magnetics
   • Handles the physical Ethernet connection and interfaces with the LAN8720.
3. Capacitors
   • For decoupling and DC blocking, e.g., 0.1µF for decoupling, as recommended per design.
4. Resistors
   • Pull-up or pull-down resistors as required for configuration, typically 4.7kΩ to 10kΩ.
5. 50 MHz Crystal Oscillator
   • If required, to provide the necessary clock signal to the LAN8720.

1. Search and Add Components:
   • Use Flux's component search to find and add the $LAN8720$ and appropriate RJ45 connector.
   • Add capacitors and resistors from the component library.
2. Connect Components:
   • ESP32 to LAN8720: Connect using the RMII interface as previously discussed.
   • LAN8720 to RJ45: Make sure to include capacitors for coupling.
   • Connect decoupling capacitors near power pins.
3. Check Pin Configurations:
   • Ensure the pins such as $TXD0$, $RXD0$, $TX_EN$, $CRS_DV$, $MDC$, and $MDIO$ are correctly connected between the ESP32 and LAN8720.
4. Review and Simulate:
   • Once all components are placed and routed, review the schematic to ensure accuracy.

• ESP32:IO0 (CLKETH) to:
  • LAN8720:XTAL1/CLKN (if used for clock input)
• ESP32:IO17 (CRS_DV) to:
  • LAN8720:CRS_DV/MODE2
• ESP32:IO19 (TXD0) to:
  • LAN8720:TXD0
• ESP32:IO22 (TX_EN) to:
  • LAN8720:TXEN
• ESP32:IO25 (RXD0) to:
  • LAN8720:RXD0/MODE0
• ESP32:IO26 (RXD1) to:
  • LAN8720:RXD1/MODE1
• ESP32:IO27 (MDC) to:
  • LAN8720:MDC
• ESP32:IO23 (MDIO) to:
  • LAN8720:MDIO

• LAN8720:TXP and TXN to:
  • RJ45: Through DC blocking capacitors (usually 0.1µF)
• LAN8720:RXP and RXN to:
  • RJ45: Using transformer coupling (via integrated magnetics or external magnetics)

• Connect ESP32 3.3V to:
  • LAN8720:VDD2A and VDDIO for power supply
• Ensure all GND pins of the components are connected to a common ground plane.

• Consider a 50 MHz oscillator connected to LAN8720:XTAL1/CLKN if the ESP32 is not used as a clock source.
• Place decoupling capacitors (e.g., 0.1µF) near each power pin for noise filtering.
• Pull-up resistors as needed, especially to reset lines.

• IO0:
  • May connect to XTAL1 or internal clock as a source.
• CRS_DV:
  • Connect to CRS_DV/MODE2.
• TXD0:
  • Connect to TXD0.
• TX_EN:
  • Connect to TXEN.
• RXD0:
  • Connect to RXD0/MODE0.
• RXD1:
  • Connect to RXD1/MODE1.
• MDC:
  • Connect to MDC.
• MDIO:
  • Connect to MDIO.

• Ensure all GND pins on both U1 and U2 are connected to a common ground plane for reference voltage stability.
• Connect 3.3V to VDD2A and VDDIO for power.

• Connect the input pin of the regulator to your higher voltage source. Ensure this input voltage is within the regulator's specified range, e.g., 5V or higher.

• Connect the output pin of the regulator to the 3.3V rail. This will be used to power the ESP32 $U1$ and the LAN8720 $U2$.

• Connect the ground pin of the regulator to the common ground plane.

• Input Capacitor: Place a capacitor, e.g., 10µF, near the input pin to stabilize any voltage fluctuations from the power source.
• Output Capacitor: Place a capacitor, e.g., 10µF, at the output to smoothen the 3.3V rail.

• VIN (Input Voltage Source) to Regulator VIN
  • Regulator VOUT to 3.3V rail (distributing to U1's 3.3V and U2's VDD pins)
  • Regulator GND to GND plane

• 10µF capacitor between VIN and GND
• 10µF capacitor between VOUT and GND

• Regulator:VIN to your input power source.
• Regulator:VOUT to $U1:3.3V$ and $U2:VDD2A, VDDIO$.
• Regulator:GND to a common ground.

• Regulator: LM1117-3.3 (or a similar 3.3V regulator)
• Input Capacitor: 10µF
• Output Capacitor: 10µF

1. Input Voltage Supply to Regulator:
   • Connect VIN of the voltage regulator to your higher input voltage source (e.g., from VIN on a header or power jack).
2. Output of Regulator:
   • Connect the VOUT of the regulator to your 3.3V power rail.
   • This line will power $U1:3.3V$ and $U2:VDD2A$ and $U2:VDDIO$.
3. Ground:
   • Connect GND of the regulator to the common ground plane shared by all components.
4. Decoupling Capacitors:
   • Input Capacitor: Connect a 10µF capacitor between VIN and GND.
   • Output Capacitor: Connect a 10µF capacitor between VOUT and GND.

• Connect Regulator:VIN to input power source.
• Connect Regulator:VOUT to $U1:3.3V$, $U2:VDD2A$, and $U2:VDDIO$.
• Connect Regulator:GND to GND plane.
• Place 10µF capacitor between VIN and GND.
• Place 10µF capacitor between VOUT and GND.

1. 3.3V: Already a regulated output we cannot use directly as input.
2. EN: Could be used to enable the power circuit.
3. GND: Ground connection.
4. VIN: Unregulated input voltage (e.g., 5V or more).

1. Power Input via VIN:
   • Connect SL1:VIN to Regulator:VIN. This will serve as the unregulated input for the LM1117-3.3 (or similar) voltage regulator.
2. Ground Connection:
   • Connect SL1:GND to the common ground plane, including Regulator:GND, $U1:GND$, and $U2:GND$.
3. Enable Pin Usage:
   • Use the SL1:EN pin to potentially control enabling the circuit, if desired. This can be connected to a control pin on the ESP32 or a logic circuit.
4. 3.3V Output:
   • Since SL1 includes a 3.3V pin, ensure this pin SL1:3.3V is left unconnected or used as an output to monitor the power status if needed, but it should not be used as an input source.

• Connect SL1:VIN to Regulator:VIN.
• Connect SL1:GND to GND plane.
• Optionally use SL1:EN for power control logic.

• 10µF on Regulator:VIN to GND (input side)
• 10µF on Regulator:VOUT to GND (output side)

• Purpose: Stabilizes input voltage and reduces noise.
• Value: Typically 10µF (Electrolytic or Ceramic).
• Connection:
  • Connect the positive terminal to Regulator:VIN and the negative terminal to Ground (GND).

• Purpose: Stabilizes the output voltage and helps reduce voltage fluctuations.
• Value: Typically 10µF (Electrolytic or Ceramic).
• Connection:
  • Connect the positive terminal to Regulator:VOUT and the negative terminal to Ground (GND).

1. Search and Add Components:
   • Use Flux's component library to search for and add two 10µF capacitors.
2. Place Capacitors:
   • Place one capacitor on the input side of the regulator, connecting between SL1:VIN and GND.
   • Place the other capacitor on the output side of the regulator, connecting between Regulator:VOUT and GND.
3. Ensure Proximity:
   • Place these capacitors close to the regulator pins on your PCB layout to maximize their effectiveness.

• Input Capacitor C1:
  • Connect C1: + to Regulator:VIN
  • Connect C1: - to GND
• Output Capacitor C2:
  • Connect C2: + to Regulator:VOUT
  • Connect C2: - to GND