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      Arduino Ethernet

      The Arduino Ethernet, based on the ATmega328 found in the Uno, can connect to an Ethernet network, a functionality needed in a number of projects. Physically, the Arduino Ethernet has the same 14-digital inputs/outputs as the Arduino Uno, with the exception that 4 are used to control the Ethernet module and on-board micro-SD card reader, limiting the amount of pins available.

      It is interesting to note that the Arduino Ethernet has an optional POE module, short for Power Over Ethernet. This option enables the Arduino Ethernet to be powered directly from an Ethernet connection, without the need for an external power source provided that there is a POE supply on the other end of the Ethernet cable. Without POE, the Arduino must be powered by an external source

Another difference from other Arduino boards is the lack of a USB connector. Because most of the space is taken up with an Ethernet connector, this device instead supports a 6-pin serial programming header and is compatible with numerous programming devices (including a device from Arduino, the USB-Serial adapter). The Arduino Ethernet is shown in Figure 1.5.

Figure 1.5 The Arduino Ethernet

      Arduino Mega 2560

      The Arduino Mega 2560 is only slightly larger than the Arduino Uno, but it has more input and output pins. It has a total of 54 digital I/O pins and 16 analog inputs. It also has a large amount of flash memory: 256 KB, capable of storing larger programs than the Uno. It also has generous SRAM and EEPROM: 8 KB and 4 KB, respectively. It also has 4 hardware UART ports, making it an ideal platform for communicating with multiple devices serially.

Arduino Mega boards are used when large amount of inputs and outputs are required. It is shown in Figure 1.6.

Figure 1.6 The Arduino Mega 2560

      Arduino Mini

The Arduino Mini is a tiny device, useful for applications where space is reduced to the absolute minimum (see Figure 1.7). It has 14 digital I/O pins and 4 analog input pins. (Four more are available but are not broken out.) The device has the strict minimum: it does not have a USB connector; it has no power regulator; and it has no headers. Programming is done via an external USB or RS232 to TTL serial adapter. It is shown in Figure 1.7.

Figure 1.7 The Arduino Mini

      Arduino Micro

      The Arduino Micro lives up to its name; it is one of the smallest Arduino boards available. Despite its small size, it still has a large amount of input and output pins; it has 20 digital input/output pins, of which 7 can be used as PWM outputs. It also has 12 analog inputs.

The Micro is not designed to have shields but it does have an interesting layout, as shown in Figure 1.8. It can be placed directly onto a breadboard.

Figure 1.8 The Arduino Micro

      Arduino Due

      The Arduino Due differs from all other Arduino designs in that it is not based on an AVR, but rather uses a microcontroller based on an ARM Cortex-M3, the Atmel SAM3X8E. This advanced microcontroller is clocked at 84 MHz and is a full 32-bit device. It has a large amount of digital and analog I/O: 54 digital pins (12 of which can be used as PWM) and 12 analog inputs. The board has 4 UARTs, an SPI header, a Twin-Wire Interface, and even includes a JTAG header.

      The Arduino Due has more strict power supply requirements, and the microcontroller itself is powered under 3.3 V. Be careful not to apply 5 V to any of the pins: otherwise, you will damage the board. When choosing a shield for the Due, make sure the shield supports 3.3 V. You can identify if a shield is Due compatible by making sure it conforms to the Arduino R3 layout.

The Arduino Due is an incredibly powerful Arduino. The Due has 512 KB of flash memory and a total of 96 KB of SRAM. It can handle the largest programs at a fast speed. If you have a lot of calculations to perform, this is the Arduino that you need (Figure 1.9).

Figure 1.9 The Arduino Due

      LilyPad Arduino

      The LilyPad Arduino is an interesting device. It strays from the typical Arduino build because it is not rectangular, but round. Secondly, it does not support shields. What it is designed for, however, is to be a small device that is perfect for wearable computing, or e-fabric. The round shape means that connectors are evenly distributed, and its small scale (2 inches in diameter) makes it perfect for wearable devices. This device is easily hidden, and multiple manufacturers have designed devices especially for the LilyPad: Wearable LEDs, light sensors, even battery supply boxes that can be sewn into fabric.

To make the LilyPad as small and as light as possible, some sacrifices were made. The LilyPad does not have a voltage regulator, so it is vitally important to deliver at least 2.7 volts, but more important, no more than 5.5 volts; otherwise, the LilyPad will be destroyed (see Figure 1.10).

Figure 1.10 The LilyPad Arduino

      Arduino Pro

      The Arduino Pro exists in two versions, based either on the ATmega168 or the ATmega328. The 168 version operates at 3.3 V with an 8 MHz clock, and the 328 version runs on 5 V at 16 MHz. Both versions

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