Low cost Ethernet shield with ENC28J60
Economical alternative to original Arduino ethernet shields, allows data rates up to 10 Mbps and is achieved with a traditional assembly components.
One of the most interesting shield that you can mount on the Arduino platform is certainly the ethernet shield, because enable numerous networking applications such as remote control of systems and users, web access and publication of data, and more yet, the simplicity of finding and integrating open-source libraries on Arduino IDE does the rest. The usefulness of LAN connectivity has meant that the market would respond by offering different ethernet shield, first of all the original Arduino Ethernet Shield, which was accompanied by the good shield by Seeed Studio, both of these circuits are based on the chipset WIZnet W5100, allow multiple socket connections and can work at 100 Mbps.
This ethernet shield is low-cost thanks to components used: all traditional mounting (THT). This feature makes the circuit accessible to those who haven’t the equipment to assemble SMD components. The data-rate is limited to 10 Mbps.
The shield is based on a Microchip ENC28J60 chip that interfaces with Arduino and data conversion according to the ethernet protocol. It integrates the MAC controller, an 8 KB Transmit / Receive Packet Dual Port Buffer and a circular FIFO managed at the hardware level, allows the programming of data retransmission in case of collision.
The MAC controller supports both Unicast, Multicast and Broadcast packets, has a programmable 64-byte pattern within a margin allowed to the user and programmable wake-up on multiple packet formats (Magic Packet, Unicast, Multicast, Broadcast, specific packet match or any packet).
In the circuit we see that over all’ENC28J60 there are a standard RJ45 jack with integrated LEDs, filters and line transformers, and a voltage level shifter for the SPI interface to communicate with the Arduino.
MISO is the output data of the slave device and the input of Arduino, while MOSI is the opposite; SCK is the clock that marks the two-way communication on the SPI bus and RESET the reset line, which is also connected to a button that allows you to reset the Ethernet interface, if necessary, manually. The digital D10 and D2 lines of Arduino are used, respectively, for the control of CS (Chip Select, active logic zero) and the reading of INT. U3B is used to adapt the logic levels 0/3, 3 V to those of Arduino 0/5 V.
The ENC28J60 operates with a clock of 25 MHz, defined by the quartz Q1 connected between the pins 23 and 24; the capacitor connected to pin VCAP filters the output voltage (2.5 V) of the internal controller and should preferably be of the type low ESR (low series resistance parasite). The resistor connected to RBIAS is used to bias the LAN transceiver that is part of the pin TPIN + / – and TPOUT + / -.
We conclude the analysis of the circuit diagram of the shield with the power that is drawn by Arduino 5V and Vin through the strip: the first provides the 5 volts continuous stabilized points of the circuit that require them (basically the 74HC125 and the resistance of pull Line-up reset and Chip Select) and the second give power to the integrated regulator U2, which creates the 3.3 volts needed to power the microcontroller and circuits contained in the RJ45 jack.
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