Input/Output

Input/output (I/O) shields are available that bring out the various I/O pins of the Arduino to connectors that are more robust than the pins on the Arduino circuit board (or, in the case of the Arduino Nano, the pins below the board are connected to terminal block–type connectors on a carrier for the Nano PCB).

I/O shields can be broadly classified as either extension shields or expansion shields, although the term “expansion shield” is often applied to both types. An extension shield brings out the I/O pins from an Arduino without altering the signals—it just uses different types of connectors. A true expansion shield, on the other hand, employs active electronics to increase the number of discrete digital I/O channels. These types of shields use either SPI or I2C to communicate with the host Arduino board.

I/O Extension Shields

This category of shield is used to route the input/output signals from the AVR chip to connectors that are more robust than the pin sockets used on an Arduino board. Some I/O extension shields may offer active buffering of some type, but most simply bring out the signals from the Arduino board. These are sometimes referred to as expansion shields, but that is not really correct. They simply transfer the existing signals from one connector on the Arduino to another on the shield.

SainSmart Sensor Shield

This is a stackable shield (note the offset pin and socket strips in Figure 8-3). The AVR I/O is brought out as latching multipin sockets, pin header blocks, and positions for two 10-pin headers suitable for use with ribbon cable IDC-type connectors. A reset switch is also provided. This shield can be used with any Arduino board with the baseline pin configuration, including the Mega boards.

Figure 8-3. SainSmart I/O expansion (sensor interface) shield

Figure 8-4 explains the large modular connectors along the edges of the shield PCB. These are multipin connectors, sometimes referred to as “buckled” connectors, that mate with corresponding three- and four-pin plugs. The multiconductor cables are common and can be obtained from multiple vendors. One source (other than SainSmart) is TrossenRobotics.

Figure 8-4. SainSmart I/O expansion shield pin and connector layout

TinkerKit Sensor Shield

This stackable shield (Figure 8-5) uses long-lead pin sockets, 12 three-pin connectors, and 2 four-pin connectors. A reset switch is located between the four-pin connectors.

Figure 8-5. TinkerKit I/O expansion shield

The TinkerKit sensor shield was originally designed to work with the various sensor and motor modules produced by TinkerKit, but it can be used like any other I/O extension shield. Figure 8-6 shows the layout of the connectors on the PCB. These employ a three-wire scheme like that used with the SainSmart board shown previously. For more about the TinkerKit modules designed for use with this shield, refer to Chapter 9.

Figure 8-6. TinkerKit I/O expansion shield connectors

Although the status of TinkerKit is currently in limbo, the products are still available from Mouser and other sources. The software libraries are available on GitHub.

TinkerKit Mega Sensor Shield

The TinkerKit Mega Sensor Shield (Figure 8-7) is designed to bring out the additional I/O pins of an Arduino Mega, Mega2650, or Mega ADK board. It utilizes long-lead pin sockets for stackability, and a reset switch is provided on the PCB. It is essentially a larger version of the TinkerKit shield described previously.

Grove Base Shield

A module and shield system gaining popularity among Arduino users are the Grove components sold by Seeed Studio. These are a large number of modules to select from, and a base board is available that features an integrated Arduino-compatible ATMEGA328p MCU. The board, designed by Linaro.com (96Boards.org) is shown in Figure 8-8.

Figure 8-7. TinkerKit I/O expansion shield for Mega-type Arduino boards

Figure 8-8. Grove Base Shield

Seeed Studio also sold a passive (that is, no onboard MCU) expansion shield for the Grove module system, but while you may still be able to find some, they have been discontinued. The Passive Seeed Studio Grove Base Shield is shown in Figure 8-9.

Figure 8-9. Seeed Studio Passive Grove Base Shield

For more information about the Grove series of modules and compatible interface shields, visit the Seeed Studio wiki.

CuteDigi Sensor Expansion Shield

Technically an I/O extension shield rather than a true expansion shield, this shield from CuteDigi (Figure 8-10) uses pin headers instead of connectors to bring out the signals from an Arduino Mega-type board. It is not stackable, but given the vertical arrangement of the pins on the PCB it wouldn’t make sense to stack something on top of this board. The labels on the PCB are clear and the functions obvious.

Figure 8-10. CuteDigi Mega extension shield with SD flash and bluetooth connections

This shield is interesting in that it also includes a header with right-angle pins for connecting to an SD-type flash card carrier, and there is a pin header for use with a Bluetooth module as well. The connectors employ the same S-V-G (signal, V+, ground) scheme seen on other I/O extension shields.

I/O Expansion Shields

Unlike the I/O extension shields listed in the previous section, an I/O expansion shield provides additional I/O capabilities, usually in the form of discrete digital I/O (although some shields do have analog capabilities). Because these shields have active circuitry in addition to various connectors, they are more expensive than extender shields. Their big advantage lies in providing multiple I/O channels using only an I2C or SPI connection to the underlying Arduino board. This leaves the remaining pins on the Arduino available for other applications.

Macetech Centipede Shield

The Macetech Centipede Shield (Figure 8-11) uses the Arduino I2C interface to provide 64 general-purpose discrete digital I/O pins. The pins are arranged as 4 groups of 16 pins, with each group controlled by an I2C I/O expander chip.

Figure 8-11. Macetech Centipede I/O expansion shield

Figure 8-12 shows the layout of the I/O pins used on the Macetech shield. Each of the MUX (multiplexer) ICs controls 16 pins, or one block of I/O pins. Notice how the pin numbering is arranged on each block, with the numbering “wrapping” around the block.

LinkSprite I/O Expander Shield

This is a stackable shield that uses an MCP23017 I2C I/O expander chip to provide an additional 16 discrete digital I/O pins (Figure 8-13). Note that this shield is designed for use with R3-style Arduino boards and uses the last two pins (9 and 10, SDA and SCL) on the extended connector found on Uno R3 and Leonardo boards.

Figure 8-12. Macetech Centipede I/O pin layout

The expanded I/O pins are arranged as two sets of eight discrete channels, designated GPIOA and GPIOB. As shown in Figure 8-14, these are positioned next to the digital I/O pin socket strips. This might make it awkward to use these pins if another shield is stacked on top of this one, so be aware of little “gotchas” like that. But if it’s the only shield, or the top shield in a stack, then it shouldn’t be a problem.

Numato Digital and Analog IO Expander Shield

The digital and analog expander shield from Numato (Figure 8-15) provides 28 additional discrete digital I/O channels and 16 analog inputs using two MCP23017 I2C digital I/O chips and an NXP 74HC4067 analog multiplexer IC for analog signals.

Figure 8-13. CuteDigi 16-channel I/O expander shield

Figure 8-14. CuteDigi 16-channel I/O expander shield pin layout

As shown in Figure 8-16, the primary interface to an Arduino is via the I2C interface on pins A4 and A5. The interrupt pins on the MCP23017 chips are also brought out on the digital I/O pin blocks. The six pin headers in the middle of the board are used with jumper blocks to select the I2C addresses of the two MCP23017 chips.

Figure 8-15. Numato digital and analog I/O expansion shield

Figure 8-16. Numato I/O expansion shield pin layout

Relay Shields

Relay shields are available with one or more relays. The relays used in these shields may be 5- or 10-ampere types like the ones shown on the shields listed here, as well as reed relays in DIP packages.

DFRobot Relay Shield

This shield shows how the form factor of a shield can be “tweaked” to accommodate larger parts. In the case of the DFRobot relay shield (Figure 8-17), the four relays are mounted in an expanded part of the shield PCB. The relay contacts are rated at 3A nominal at 24V DC or 120V AC, with 5A maximum current capacity. This is a stackable shield, although the vertical I/O pins may be difficult to use with a shield on top of this board.

Figure 8-17. DFRobot relay shield

The board uses a set of jumpers to route the digital signals for the relay drivers and an XBee module’s pins, shown in Figure 8-18. All of the Arduino’s digital and analog pins are brought out in blocks of pin headers.

Figure 8-18. DFRobot relay shield board layout

Numato Relay Shield

This shield (Figure 8-19) uses two low-power modular relays with contacts rated for 1A at 120V AC and 2A at 24V DC. The Numato shield uses the Arduino’s digital pins 2 and 3. Miniature terminal blocks bring out the relay terminals. This is a stackable shield.

Figure 8-19. Numato relay shield

Seeed Studio Relay Shield

The Seeed Studio relay shield (Figure 8-20) uses four relays with contacts rated at 10A at 120V AC. It uses the Arduino’s digital output pins 4 through 7, one per relay. Each relay has an LED to indicate activity. This is a stackable shield.

Figure 8-20. Seeed Studio relay shield

Signal Routing Shields

There aren’t a lot of signal routing shields available. What shields are available typically come in one of two styles: passive routing or active MUX (multiplexer) routing.

Adafruit Patch Shield

The passive patch shield available from Adafruit, shown in Figure 8-21, allows you to route signals between four RJ45-type connectors (also known as 8P8C connectors) and the underlying Arduino board using short patch wires inserted into blocks of pin sockets.

Note

This is a kit, not an assembled shield. The photo shows what the assembled shield should look like.

Figure 8-21. Adafruit patch shield

The main idea behind the patch shield is to route specific signals to and from an Arduino through conventional Ethernet cables to remote connection points, as shown in Figure 8-22. The kit includes four satellite PCBs with 8P8C (RJ45) jacks and pins to connect to a solderless breadboard, a sensor module, or another Arduino. There are no active components on this shield or the satellite boards; it just routes signals.

Figure 8-22. Adafruit patch shield layout and usage

Mayhew Labs Go-Between Shield

The Go-Between shield (Figure 8-23) employs a matrix of solder jumper locations to route signals from the base Arduino or a lower shield to an upper shield. It could be handy if you want to stack two shields that use the same pins for I/O functions. If the pins of the upper shield could be moved to different pins on the lower shield without any shield hacking, that would solve the problem. A minor change to the software would make it all work.

Figure 8-23. Mayhew Labs Go-Between shield

Mayhew Labs Mux Shield II

The Mux Shield II (Figure 8-24) is an active shield that supports up to 48 inputs or outputs using three Texas Instruments CD74HC4067 multiplexer chips and three output shift register circuits. The board uses four of the Arduino digital pins to control the MUX chips and shift registers. The default digital pins are 2, 4, 6, and 7. Pins A0, A1, and A2 of the Arduino are used as inputs from the MUX chips.

The 3 × 16 array of pads (Figure 8-25) can be used with pin headers or pin sockets. Each channel is bidirectional, routing signals to a common output or from a common input. Each MUX chip is similar to an array of switches, each with a slight resistance while closed, and a very high impedance when open.

Figure 8-24. Mayhew Labs active signal multiplexer shield (Mux II)

Figure 8-25. Mayhew Labs signal multiplexer shield pins

Mayhew Labs Mux Shield

Similar to the shield described previously, this active multiplexer shield provides 48 programmable I/O lines using three TI CD75HC4067 MUX chips (see Figure 8-26). It also provides two large blocks of pin socket headers to access the signals. The Arduino’s digital pins 2 through 5 are used to address the MUX chips, and pins A0, A1, and A2 are the analog inputs from the MUX chips. This is a stackable shield.

Memory

Without a doubt, the SD and microSD flash memory formats are the most popular way to add some file-like memory to an Arduino. External flash memory is accessed through the SPI interface, and an SD or microSD socket is often found as an added feature on shields that are using the SPI for the primary function (Ethernet, WiFi, USB host, etc.). Removable flash memory is a convenient way to log data from a standalone Arduino, and then later load the data into your PC and do whatever it is you want to do with it.

These descriptions don’t have accompanying diagrams, mainly because the SD or microSD interface to an Arduino is just an SPI interface. One shield has the select signal on an unusual pin. That might create a conflict with existing software.

Figure 8-26. Mayhew Labs active signal multiplexer shield (Mux)

Seeed Studio SD Card Shield

Designed for full-size SD flash memory cards, this shield (shown in Figure 8-27) can easily be used with microSD cards with an adapter. Arduino digital pins D4, D11, D12, and D13 are used for the SPI interface. The shield also brings out the ICSP, I2C, and UART pins to connectors on the PCB. This is a stackable shield.

Figure 8-27. Seeed Studio SD memory card shield

SHD-SD SD Card Shield

This SD shield, pictured in Figure 8-28, features a small prototyping area for adding your own circuitry. It can accept microSD cards with an adapter. The shield uses the D10, D11, D12, and D13 pins on an Arduino for the SPI interface to the SD memory. It also uses the 3.3V DC from the Arduino. The shield is shorter than a conventional shield, with a baseline Arduino pin arrangement. It is a stackable shield.

Figure 8-28. Short SD card shield

SparkFun microSD Shield

The SparkFun microSD shield (Figure 8-29) accepts only microSD cards. It includes a large 12 by 13 prototyping area. It does not come with pin sockets or headers, but these can be ordered separately. It uses the D10, D11, D12, and D14 pins on an Arduino.

Figure 8-29. SparkFun microSD shield

Communication

Although an Arduino might have a USB interface (most do) with the ability to act as a serial port from the host system’s perspective, or an Ethernet jack as found with the Arduino Ethernet, a basic Arduino like an Uno or Leonardo doesn’t really have much in the way of plug-and-play data communications interfaces. It is possible to attach level-shifting chips and use the built-in UART or write a so-called “bit-banger” to send serial data, but it is sometimes more convenient to use something with an SPI interface to the Arduino and let it do the serial sending and receiving. For other forms of data communication the necessary external hardware can get rather involved, so it’s definitely easier to use a ready-made shield.

Serial I/O and MIDI

Although even Ethernet can be considered a form of serial data communication, serial I/O here refers to the old standards of RS-232 and RS-485. While these are old, they are ubiquitous. Older PCs have RS-232 connectors (and quite a few newer models also have at least one), and RS-485 is common in instrumentation, testing, and distributed measurement systems.

CuteDigi RS232 Shield

This RS-232 shield (Figure 8-30) employs a MAX232 IC to perform the signal-level shifting necessary to send and receive RS-232–compatible signals. A bank of jumpers is used to configure the serial interface, and any two digital pins from D0 to D7 on an Arduino may be used for the serial interface. With the supplied pin sockets installed it becomes a stackable shield.

Figure 8-30. CuteDigi RS232 shield

CuteDigi RS-485 Shield

CuteDigi’s RS485 shield (Figure 8-31) uses a MAX481CSA chip to provide the RS485 electrical interface using the Arduino’s Rx and Tx ports (D2 and D3, respectively). A mounting position is provided in the shield PCB for an optional DB-9 connector. This is a stackable shield.

Figure 8-31. CuteDigi RS485 shield

SparkFun MIDI Shield

MIDI is a venerable serial protocol that has been around for over 30 years. It is used to control musical synthesizers, sequencers, drum machines, and mixers, among other things. The SparkFun MIDI shield (Figure 8-32) uses the Arduino’s USART pins to send and receive MIDI event messages.

Figure 8-32. SparkFun MIDI shield

The MIDI shield uses the D0 and D1 pins (Rx and Tx, respectively) for MIDI serial I/O. It also has pushbuttons on D2, D3, and D4; LEDs connected to D6 and D7; and potentiometers connected to A0 and A1.

Ethernet

Ethernet shields are popular, and the Arduino IDE comes with a fairly comprehensive Ethernet library suite (see Chapter 7 for details). Be aware that the communication between the AVR MCU on the Arduino board and the Ethernet controller on the shield uses the SPI interface. The AVR does not have DMA (direct memory access) capability, and it has no external memory to directly access in any case.

With Ethernet shields that use SPI as the interface with an Arduino there is an inherent limit on how fast data can move between the AVR MCU and the Ethernet I/O chip, and consequently on how fast data can move over the Ethernet connection. It is simply not possible to get 100 Mb/s (100Base-T) data rates with a processor running at 20 MHz using an SPI interface, and 10 Mb/s (10BASE-T) is an unlikely stretch. 5 Mb/s is a more realistic expectation. The data is still sent out over the physical layer (the actual Ethernet) at 10 Mb/s, just in byte-sized dribbles rather than as a continuous stream. It all depends on how quickly the software running on the AVR can assemble outbound data and send it to the Ethernet chip. So, while it is possible to create a web server that can fit into a tiny enclosure like an old mint tin, it isn’t going to be very fast, and it won’t handle a lot of connections at the same time.

Where the Ethernet interface really shines is when it is used as the end node of a remote sensing or control system. You can attach it to the Internet, implement some password protection, and use it to retrieve data from some remote location. It can be used to report data back to a central controller in an industrial setting such as a factory, or it can be used to sense temperature, humidity, and other parameters for a distributed HVAC (heating, ventilation, and air conditioning) system controller like the one described in Chapter 12.

Vetco Ethernet Shield with microSD Card Reader

This Ethernet shield from Vetco (Figure 8-33) also includes a microSD card carrier and a reset button. The Arduino’s digital pins D10, D11, D12, and D13 are used for the SPI interface used by the WIZnet W5100 Ethernet chip and the microSD card socket. It is a stackable shield.

Figure 8-33. Vetco Ethernet shield

Arduino Ethernet Shield R3 with microSD Connector

The official Ethernet shield from Arduino comes with a microSD card reader, a reset button, and all the necessary electronics to implement the Ethernet interface (see Figure 8-34). It uses digital pins D10, D11, D12, and D13 for the SPI interface. This is a stackable shield.

Figure 8-34. Arduino Ethernet shield

Bluetooth

Bluetooth is a low-power, short-range wireless communication technology originally intended to replace the cables strung between a computer and external devices such as printers, keyboards, mice, and so on. While it is still used for these applications, it has found use in many other types of communications applications. There are a number of Bluetooth shields available.

Bluetooth Shield

This shield comes assembled with a Bluetooth module already mounted on the PCB. Note that it is a stackable shield that is shorter than a typical shield. The antenna is the gold pattern emerging from the end of the Bluetooth module (see Figure 8-35). It uses the Rx and Tx pins (D2 and D3, respectively).

Figure 8-35. DealeXtreme Bluetooth shield

Seeed Studio Bluetooth Shield

This compact, stackable Bluetooth shield (Figure 8-36) uses an Arduino’s Rx and Tx pins. It also brings out the pins for analog and digital signals to interface with sensor modules.

ITEAD Bluetooth Wireless BT Module Shield Kit

This shield (Figure 8-37) uses a standard Bluetooth module, and comes with a prototyping area on the PCB. It is a “short” shield, in that it doesn’t cover the whole length of an Arduino board. It is stackable.

DFRobot Gravity:IO Expansion Shield

This multifunction board from DFRobot (Figure 8-38) combines I/O extension capabilities with a set of pin sockets for a Bluetooth or ZigBee wireless module. It is not a stackable board.

Figure 8-36. Compact Bluetooth shield from Seeed Studio

Figure 8-37. ITEAD Bluetooth shield with prototyping area

Figure 8-38. DFRobot multifunction shield with Bluetooth

USB

One thing an 8-bit Arduino can’t do is act as a USB host to other USB devices. A USB host shield allows you connect USB devices such as keyboards, printers, some test instruments, and various toys to an Arduino.

ITEAD USB Host Shield

This is a stackable shield with USB host functionality. It also provides pins for the Arduino digital and analog signals, and two 10-pin positions on the PCB for either connectors or pin headers (see Figure 8-39). It is based on a MAX3421E chip with an SPI interface to an Arduino.

Figure 8-39. USB host shield with I/O connections

Circuits@Home USB Host Shield

This shield (Figure 8-40) supports USB 2.0 full-speed operation and uses an SPI interface to an Arduino. The digital and analog signals from the Arduino are available on the shield’s PCB, and with the right pin sockets it could be stackable. It employs a MAX3421E chip with an SPI interface to an Arduino using pins D10, D11, D12, and D13. It does not come with pin sockets or headers.

Arduino USB Host Shield

Like other USB host shields, this board uses the MAX3421E chip with an SPI interface to the Arduino using pins D10, D11, D12, and D13. Three- and four-pin connectors bring out input and output ports that will work directly with TinkerKit modules (the TinkerKit modules are described in Chapter 9). This is a stackable shield (see Figure 8-41).

Figure 8-40. Circuits@Home USB host shield

Figure 8-41. Arduino USB host shield with I/O connectors

ZigBee

ZigBee is a popular low-power wireless protocol. Many of the available ZigBee Arduino shields use readily available XBee modules, but most shields will accommodate any RF module with the correct pinout. Some are available with an XBee module, and some are available without. A 1 mW XBee module costs around $25.

Arduino Wireless SD Shield

On this ZigBee shield (Figure 8-42), two inline pin sockets are provided for a Digi XBee module, or any module with a compatible pin arrangement. This shield uses an Arduino’s pin D4 as the select, and pins D11, D12, and D13 for SPI communication. A microSD carrier on the shield also uses the SPI interface.

Figure 8-42. Arduino ZigBee shield

SainSmart XBee Shield

This shield comes without an XBee module, but the pin layout will accept a standard XBee module, or any module with a compatible pin arrangement. Note that there is no microSD carrier. This is an offset stacking shield (note the locations of pin headers and pin sockets in Figure 8-43).

Figure 8-43. SainSmart compact ZigBee shield

Seeed Studio XBee Shield

The XBee shield from Seeed Studio (Figure 8-44) has the expected mounting position for a common XBee module, and it also provides a prototyping area. This shield uses the Rx and Tx pins from an Arduino, and a block of pins for jumpers is used to route the Rx and Tx signals from the Arduino to the wireless module.

Figure 8-44. SainSmart ZigBee shield with prototyping area

CAN

The Controller Area Network (CAN, also known as CAN bus), is a differential signalling relative of RS-485 found in vehicles, industrial settings, and some military equipment. It is relatively fast (up to 1 Mb/s), incorporates signal collision detection and error detection, and supports multiple nodes. It is used with the OBD-II on-board diagnostics found in late-model automobiles, in electric vehicles, and with distributed sensors in scientific instruments, and has even been integrated into some high-end bicycles.

Seeed Studio CAN-BUS Shield

The CAN interface shield from Seeed Studio (Figure 8-45) utilizes an MCP2515 CAN bus controller with an SPI interface and an MCP2551 CAN transceiver chip. Both a terminal block and a DB-9 connector are provided for the CAN bus signals. The shield also brings out the I2C and UART communications from the Arduino. The pin layout is shown in Figure 8-46.

Figure 8-45. Seeed Studio CAN shield with auxiliary I/O connectors

Figure 8-46. Seeed Studio CAN shield with auxiliary I/O pin layout

SparkFun CAN-BUS Shield

This CAN shield from SparkFun (Figure 8-47) incorporates many of the features one might want to use when creating an OBD-II readout and data capture device. It has a DB-9 connector for CAN bus signals, and a 4-pin header also provides the signals. Connection points are provided for an external LCD display and an EM406 GPS module.

An interesting feature is a four-position binary joystick, and it incorporates a microSD flash card carrier. The joystick is connected to the Arduino analog inputs. The CAN chip and the SD flash are separately selected via digital pins D9 and D10. Pins D3, D4, D5, and A0 are not used by the shield. The pin layout is shown in Figure 8-48.

LinkSprite CAN-BUS Shield

The LinkSprite CAN shield (Figure 8-49) is physically similar to the Seeed shield. It has both a DB-9 connector and a two-position terminal block for the CAN signals. Pins D10, D11, D12, and D13 are used for the SPI interface to an MCP2515 CAN chip.

Figure 8-47. SparkFun CAN shield with microSD carrier and digital joystick

Figure 8-48. SparkFun CAN shield I/O pin layout

Figure 8-49. LinkSprite CAN shield

Prototyping

If you want to create your own shield you can build a prototype (or even a permanent shield) using a prototyping shield board. This is not the same as the process of creating a shield described in Chapter 10, which involves laying out a PCB for (possible) mass production. Figure 8-50 shows a prototype shield similar to those described in this section with a temperature sensor and a relay mounted on it. A potentiometer is connected to the +5V, ground, and A0 (analog input 0) pins passed through from the underlying Arduino board. The pot controls the temperature set point.

This prototype was used to control an ancient (and very dangerous) portable electric heater that used a bimetallic thermostat that couldn’t seem to hold the temperature to better than +/– 15 degrees. Since the relay is only rated to 10 amperes at 120 VAC and the heating elements were rated for 15 amps, it was used along with a 24 VAC transformer to control a 20-amp contactor. It worked pretty well, and kept my office relatively comfortable during the winter. I plan to add a tilt sensor, output temperature sensor, and fan motion detector to it. Just to be safe.

Figure 8-50. Prototype temperature sensor/controller shield

The shields in this section are representative of what is available, and none are particularly complicated. What the Arduino pins are used for is entirely up to you (it is a prototype, after all), so there isn’t much need for diagrams.

Adafruit Stackable R3 Proto Shield

This shield (Figure 8-51) comes as a kit, which means a bare PCB and a bag of parts. It’s not hard to assemble, but some soldering skill is essential.

Figure 8-51. Adafruit stackable prototype shield kit

Adafruit Mega Proto Shield

Another kit from Adafruit, this stackable prototyping shield comes with all the bits you can see in Figure 8-52. Note the double rows of solder pads for the connections along the sides of the PCB. This allows you to solder in short-lead pin sockets to gain easy access to the signals from an underlying Mega-type Arduino.

Figure 8-52. Adafruit Mega prototype shield kit

CuteDigi Assembled Protoshield for Arduino

This prototyping shield (Figure 8-53) comes fully assembled. It also has pin sockets on the PCB for access to the Arduino signals. This is not a stacking shield.

CuteDigi Assembled Protoshield for Arduino MEGA

Designed to work with a Mega-type Arduino, this shield (Figure 8-54) also features a small-outline (SOIC) mounting location for an IC. This is not a stacking shield.

CuteDigi Protoshield for Arduino with Mini Breadboard

This shield, pictured in Figure 8-55, includes a small solderless breadboard for your own circuit creations.

Figure 8-53. CuteDigi prototyping shield

Figure 8-54. CuteDigi Mega prototyping shield

Figure 8-55. CuteDigi prototyping shield with breadboard

Creating a Custom Prototype Shield

You can whip up a workable shield using nothing more than a prototyping PCB and some pin and socket connectors. The size of the PCB doesn’t really matter, so long as the pins line up with the sockets on an Arduino board.

Adafruit DIY Shield Kit

If there was award for the simplest shield kit, this would definitely be at the top of the list of contenders. Consisting of a prototyping PCB and four long-lead pin socket connectors (Figure 8-56), this shield lets you put anything you like on it. This is handy for prototyping a new shield design, or just quickly throwing something together, and it’s great for using an existing module of some type that was never intended to be connected to an Arduino.

Figure 8-56. Adafruit DIY shield kit

Unfortunately the product has been discontinued by Adafruit, but all you need is a prototyping PCB (these are readily available from multiple sources) and the pin sockets, which Adafruit and other vendors carry. Since the pin pads on an Arduino use industry-standard 0.1 inch (2.54 mm) spacing, it’s easy to make something with basic prototyping supplies that can serve as a shield.

Motion Control

Motion control is a big area of interest in the Arduino domain. From programmable mobile robots to CNC engravers, 3D printers to laser scanners, and even automated sun-following tracking controllers for solar panels and kinetic sculptures, Arduinos have been used to control DC motors, servos, and stepper motors from the outset. As you might expect, a number of shields are available for each type of motor, and this is just a small sampling of what’s available.

DC and Stepper Motor Control

Motor controller shields based on an H-bridge (a type of solid-state current routing switch) can usually be used to control either brush-type DC motors or stepper motors. Basically, these types of shields can be used to control any inductive DC load, including solenoids and relays.

Rugged Motor Driver shield

The Rugged Motor Driver Shield from Rugged Circuits (Figure 8-57) can drive either two brush-type DC motors, or one bipolar stepper motor. It is rated for up to 30V at 2.8A peak current. The shield uses the D3, D11, D12, and D13 pins for enable and direction control inputs. The enable inputs can be driven with a PWM signal for smooth control of a DC motor. Check the website for more details regarding current handling and software.

Figure 8-57. Rugged Motor Driver shield

SainSmart Motor Drive Shield

The SainSmart motor shield (Figure 8-58) is based on an L293D four-channel driver IC. It can drive four brush-type DC motors or two stepper motors at up to 10V. It features terminals for an external power supply. Check the website for more details regarding current handling and software.

Arduino Motor Shield

The motor shield from Arduino.cc (Figure 8-59) is based on an L298 dual-driver IC. It can be used with relays, solenoids, DC motors, and stepper motors. An interesting feature is the ability to measure current consumption, which can be handy for detecting a stalled motor. Also note that it has modular connectors that are compatible with various TinkerKit modules (described in Chapter 9).

Figure 8-58. SainSmart L239D Motor Drive shield

Figure 8-59. Arduino motor shield

PWM and Servo Control

The small servos used in RC models and small-scale robotics work by positioning an armature relative to a series of control pulses of varying width but at a steady frequency. The width (the “on” time) of the pulses determines the rotation angle of the servo. A PWM/servo shield can also be used to drive a DC motor, precisely control the brightness of one or more LEDs, or operate a linear actuator.

16-Channel 12-bit PWM/Servo Shield

This shield (Figure 8-60) utilizes a PCA9685 16-channel PWM controller IC with an I2C interface. It has the ability to generate a unique programmable PWM signal on each output, and it doesn’t require the constant attention of the Arduino.

Figure 8-60. Adafruit PWM/servo shield with I2C interface

LinkSprite 27-Channel PWM Servo Shield

This shield from LinkSprite (Figure 8-61) uses an STM32F103C8T6 microcontroller IC to generate up to 27 unique PWM outputs. It is worth noting that the STM32F103C8T6 is an ARM Cortex-M3 32-bit RISC device with up to 128 KB of flash memory and 20 KB of SRAM. The microcontroller on this shield is actually more computationally powerful than the AVR on the Arduino it is mounted on. It communicates with an Arduino using the SPI interface.

Figure 8-61. LinkSprite servo shield

SparkFun PWM Shield

The PWM shield from SparkFun (Figure 8-62) utilizes a TLC5940 IC and is capable of producing 16 PWM outputs. The TLC5940 is capable of driving LEDs or servo motors. It uses an SPI-type clocked serial interface, but only receives data. More information and software libraries are available from SparkFun.

Figure 8-62. SparkFun PWM shield

Displays

Display shields for Arduino boards might contain LED (light-emitting diode) readouts, LED arrays, an LCD (liquid-crystal display), or a color graphical display. Some of the shields utilize multiple digital outputs from an Arduino; others use the SPI or TWI (I2C) interfaces. Whatever it is you want to display, chances are there’s a display shield that will do the job.

Instrumentation Shields

Although not as plentiful as some other shield types, there are instrumentation-type shields available. These include data logging shields, logic analyzers, and precision analog-to-digital (A/D) converters. Instrumentation, in this case, refers to the ability to sense and capture data from the physical world, or generate an analog signal.

There aren’t many shields available with on-board data capture and conversion capabilities, mainly because the AVR MCU on an Arduino already has most of these functions in the chip itself. The built-in A/D converter (ADC) in the AVR MCUs used with Arduino boards has 10-bit resolution, which gives a conversion resolution of 1/1,024 per DN, or digital number. If you need better resolution (12, 16, or even 24 bits, for example), then you will need to consider some type of add-on module or a shield.

Adafruit Data Logging Shield

The Adafruit data logging shield, shown in Figure 8-74, includes an SD flash card carrier and a real-time clock (RTC) chip. The RTC can be powered by a battery when the main power from the base Arduino is off. A small prototyping grid is supplied for custom circuitry. This is not a stacking shield.

Figure 8-74. Adafruit assembled data logging shield

Adafruit Ultimate GPS Logger Shield

This shield, shown in Figure 8-75, incorporates a GPS receiver as well as an SD flash carrier and an RTC chip. The output of the GPS can be automatically logged to the flash memory card. This is not a stacking shield.

HobbyLab Logic Analyzer and Signal Generator Shield

This is actually a standalone logic analyzer on a shield. It monitors the Arduino signals without interfering with them, which is handy to see what’s happening on the I/O pins. In addition to the logic analyzer capability, it also includes an SPI decoder, a UART decoder, and a one-wire monitor. It does not communicate directly with the Arduino, but uses a USB interface to interact with a host computer. This is a stacking shield (see Figure 8-76).

Figure 8-75. Adafruit GPS data logging shield

Figure 8-76. HobbyLab logic analyzer and signal generator

Iowa Scaled Engineering 16-Channel 24-Bit ADC Shield

This shield incorporates a 24-bit A/D converter and a precision voltage reference to obtain readings from multiple single-ended or differential inputs. It also has on-board EEPROM for storing and reading calibration and configuration data. It communicates with an Arduino via the I2C (TWI) interface. This is a stacking shield (see Figure 8-77).

Visgence Power DAC Shield

One function the AVR MCU, and by extension an Arduino, lacks is a built-in digital-to-analog converter (DAC). The AVR’s internal ADC incorporates a 10-bit DAC, but the output is not available externally. Although audio output shields are readily available, there don’t seem to be a lot of pure DC output DAC shields available. The Visgence Power DAC Shield (Figure 8-78) provides three channels of analog output with the ability to source up to 250 mA of current.

Figure 8-77. Iowa Scaled Engineering 24-bit ADC data acquisition shield

Figure 8-78. Visgence 12-bit Power DAC Shield

Adapter Shields

An adapter shield is used as a physical interface between what would otherwise be two physically incompatible modules. The primary difference between an adapter shield and a signal routing shield (see “Signal Routing Shields”), at least with regard to how the shields are organized in this chapter, is that an adapter is intended as a physical interface. A signal routing shield doesn’t deal with physical differences, just signals.

Tronixlabs Australia Expansion Shield for Arduino Nano

A Nano is every bit as capable as a larger baseline Arduino, but it won’t work with conventional shields. This board, shown in Figure 8-79, addresses that by bringing out the pins from a Nano to pin headers, and optionally to standard pin socket connectors.

Figure 8-79. Tronixlabs Nano adapter shield

Arduino Nano I/O Expansion Board (eBay)

Another example of a Nano adapter (Figure 8-80). This was found on eBay, but there are others like it available.

Figure 8-80. Expansion board for Arduino Nano

Screw Terminal Shield

Although not technically a shield, per se, these handy block adapters allow you to connect up to 18-gauge insulated wire to an Arduino. They are readily available from a variety of sources. Notice that these parts have the ability to stack (see Figure 8-81).

Figure 8-81. Terminal block adapters

Miscellaneous Shields

This section describes some useful shields that don’t really fit into a neat category. I like the so-called “wing shields” because they allow for neater wiring, and the multifunction shield shown here has a multitude of uses.

Adafruit Proto-ScrewShield (Wingshield)

The Wingshield, also known as a Proto-ScrewShield, is a passive shield with two sets of miniature terminal blocks (see Figure 8-82). If you plan to incorporate an Arduino into a commercial product or a laboratory setup, then you may want to consider a shield like this. The screws in the terminal blocks provide for a much more secure and reliable connection than pin jumpers. The prototyping area in the middle of the shield can be used to mount sensor modules, or it can hold a custom circuit. The shield includes a reset switch and an LED, and it’s also a stackable shield. Be aware that this is a kit, so it comes as a bare PCB and a bag of parts. Assembly isn’t hard, but it does require some soldering skill.

DFRobot Screw ProtoShield

Like the Adafruit Wingshield this shield (Figure 8-83) provides screw terminals for each of the signals from an Arduino, but it comes fully assembled. It is also a stackable shield, so you can put it under other shields and still be able to access the terminal blocks.

DealeXtreme DIY Multifunction Shield

This is an interesting shield: it has a 4-digit numeric LED readout; an interface point for an APC220 Bluetooth module; several pushbutton switches connected to Arduino pins A1, A2, and A3; a reset switch; and a potentiometer connected to the A0 input (see Figure 8-84). Four LEDs are connected to digital pins D10, D11, D12, and D13, and a 3 × 4-pin header brings out pins D5, D6, D9, and A5, along with +5V and ground. Unfortunately this shield is also rather poorly documented, and it can take some digging to get useful information. You can find additional information on the HobbyComponents.com forum. A collection of example sketches and a schematic can be downloaded from http://bit.ly/dx-diy-sketch. Note that the directory names in the ZIP archive are all in Chinese, but most of the sketches have comments in English.

Figure 8-82. Adafruit Wingshield

Figure 8-83. DFRobot terminal block shield

The arrangement of the various components of the multifunction shield is shown in Figure 8-85. Note that this is not a stacking shield, which makes sense, because stacking another shield on top would make the LED display useless.

Figure 8-84. DX DIY multifunction shield expansion board

Figure 8-85. Multifunction shield main functional features

The schematic provided for this shield is somewhat cryptic, so I’ve created an alternate version, shown in Figure 8-86. Notice that all the Arduino pins are used by this shield. Table 8-1 lists the Arduino pins and what the multifunction shield uses them for.

This shield is a good example of what one will often encounter with a new shield board. The documentation may be minimal, and much of it might be in a language you don’t understand (Chinese, in this case, but English can be just as difficult for other people). The schematic is correct, but might be difficult to understand at just a glance, and there is no detailed pinout description. (Well, actually, there is now.)

Figure 8-86. Multifunction shield schematic

Table 8-1. Multifunction shield Arduino pin functions

Pin	Use	Pin	Use
D0	Rx from wireless module	D10	LED
D1	Tx to wireless module	D11	LED
D2	ID received input	D12	LED
D3	Annunciator control	D13	LED
D4	LED display latch	A0	Potentiometer wiper
D5	To D5 on I/O block	A1	Switch S3
D6	To D6 on I/O block	A2	Switch S2
D7	LED display clock	A3	Switch S1
D8	LED display serial data input	A4	Temperature sensor input
D9	To D9 on I/O block	A5	A5 on I/O block