PCB Shielding is the mechanical method of using conductive, magnetic or both materials to prevent EMI in the system. Mechanical shields are closed, conductive containers, connected to the ground of the PCB. They effectively decrease loop antenna sizes, and absorb and/or reflect some of the radiation.
Undesired Electromagnetic Emissions in Printed Circuit Boards
Any product with contains wires or traces and operating at high-frequency emits radio waves. As Printed Circuited Boards – PCBs become smaller and faster, one drawback of this emergent technology is severe Electromagnetic Compatibility (EMC) problems. Electronic systems consists of printed circuit boards (PCBs), interconnect, integrated chips, and I/O cables. Based on the current carried by the conductors, and the length of interconnects, these interconnects imitate antennas when working at high frequencies, sending out EMI.
Electromagnetic Compatibility – EMC
EMC determines if a device is compatible with its electromagnetic environment, and does not cause interference. If it does not emit levels of EM energy that causes electromagnetic interference (EMI) in other devices in the vicinity, it is said to be Electromagnetically Compatible. There are international standards that specify the level of emissions. Thus, manufacturers must monitor and measure electromagnetic radiation to control them. Lack of compatibility can cause narrow and broad band interference to other electronic equipment in close range, as well as data leakage.
Effects of EMI
Energy causing EMI can be in the form of conducted, radiated, and electrostatic discharge (ESD). EMI may even physically damage operational equipment, hence undesired electromagnetic (EM) emissions represent one of the most critical issues to be accounted for in electronic system design. EMC makes sure that systems perform as intended under the defined safety measures. The EMC process monitors testing requirements, and interference between the equipment placed in close proximity to each other on the PCB. Although it can occur in any frequency range, it usually occurs above 50MHz, in such cases, grounding, EMI shielding and focusing on trace spacing and layout during design phase.
Designing PCBs with EMC
There are certain simple PCB design guidelines for electromagnetic compatibility that save time and costs.
- All high-speed signals on a PCB should be referenced to a solid plane. A model return path for such signals on the circuit board is a large area of metal (ground copper polygon placed in adjacent layers to the differential pair signal), or a plane layer. This becomes the reference plane.
- Current flow in any trace on a PCB must complete the entire circuit loop and come back to the source through the reference plane. Current in a performing PCB flows from the power supply or from outputs to further downstream components.
- Return current should always choose the path of least “impedance” and will form the smallest loop with respect to the incident current path to minimize loop inductance.
One way of handling unwanted EMI is through PCB shielding.
Arduino Circuit Boards
Arduino circuit boards are produced as ready to use, and contain all required operational circuitry. Its core contains a compacted Atmega328 chip microcontroller/computer. The Arduino platform contains LEDs, connections, microcontrollers, and more. Arduino circuit boards power themselves through current supply through USB port using a USB cable. AC-to-DC power adapters can be used for external power supply.
Types of Arduino Circuit Boards
Arduino circuit boards are open source. This makes it easy for users to tailor-make projects and instruments. There are several Arduino boards available including:
- Arduino UNO,
- Red Board,
- LilyPad Arduino,
- Arduino Leonardo,
- Arduino Mega.
Each of the above are different in specifications, features and uses, and how they are used in different electronics projects. For the purpose of this article, we will focus on the Arduino Mega boards and Arduino Mega Protoshield.
Reflection and Absorption
EMI/EMC shielding can be used to encase a part of the system or the whole system. This protects the signal transmission from external noise and prevents information loss. Shielding has two chief purposes:
- Reflection (R) occurs when energy from an electromagnetic wave runs into the shield and is reflected back. and
- Absorption (A) takes place when any residual energy from the electromagnetic wave that is not reflected is absorbed in the shield, and the residual energy exits from the other side.
How to Shield a PCB
Metal shields or cans are added to shield a circuit board from EMI, in order to contain critical areas on the PCB. Shielding covering four sides and the top is soldered down to the ground plane under the components. This type of shielding is called a Faraday cage. Ideally the shield should completely enclose components to block off all emissions. However, shield openings are required for thermal cooling, seams, adjustments, and solder points to the board.
Types of PCB Shielding
PCB RF Shielding
Electromagnetic Interference shielding or EMI shielding that impedes radio frequencies and electromagnetic radiation is called RF shielding. This type of shielding reduces the coupling of radio waves, electromagnetic fields and electrostatic. A conductive enclosure used to block electrostatic fields is also known as a Faraday cage.
The Arduino EMI PCB shield is a board that can be mounted on top of the Arduino board. Its shield pins are inserted into the sockets located down both sides of the Arduino board. Arduino has a large, range of shields designed for prototyping.
Why Are Arduino Shields Better than Others?
Arduino is an Open Source Hardware Design with a great variety of low cost shields from multiple suppliers. These shields are boards plugged on top of the Arduino PCB to enhance its capabilities. Shields are easy to mount, and cheap to produce.
Arduino Shields Are Simple to Use.
Arduino Shields have an extensive sample library that makes them easy to learn and use. The library includes sample code that users can customize for tailoring assembly.
Arduino Shields Are Inexpensive.
The standard Arduino Uno is very good on the pocket, similarly most shields are also inexpensive and provide great functionality.
Arduino Shields Are Stackable
Multiple shields can be stacked on top of each other to combine their features, since there is no specific number of “slots” on the Arduino. To connect the shields, shield pins are inserted into the sockets located down both sides of the Arduino board. Stacking Arduino Mega Proto Shields together creates an entire system.
Why are Arduino Shields Stackable?
Arduino shields allow the PCB to be multi-purposed. They are stackable to combine different functionalities and package the electronics for that circuit in the same footprint as an Arduino. Arduino shields must use the pins of the Arduino board itself, so stacked shields, must use the same pins and/or GND pins, because any communication by your Arduino and another device needs a common GND.
Use of Arduino Shields
The Arduino shields placed on top of Arduino boards enhance board capabilities for the following purposes:
- Connecting to internet networks,
- Motor control,
- LCD control and
- Establishing wireless communication.
Shields may be simple or complex based on their purpose, and are sold as kits or preassembled. Kits give the flexibility of purpose building/assembling the Arduino shield as per specific needs. Some kits require you to assemble the circuitry of the boards, although more complex shields may already be largely assembled, needing only header pins.
Types of Arduino Shields
The different shields available for the use. Arduino shields are pre-built circuit boards that connect with other Arduino boards and increase compatibility between Arduino boards. Arduino Shields include:
- Wireless Shields,
- Ethernet Shield,
- GSM shield, and
- Proto Shield.
For the purpose of this article, we will focus on the Arduino Mega boards and Arduino Mega Protoshield.
Arduino Mega Shield Specifications
The Arduino Mega Proto Shield has 54 input pins and output pins. 4 of these pins are for the hardware port, 14 pins are for PWM output, and 16 pins are used as analog inputs. The Mega also has an ICSP header, power jack, one USB connection, and one REST pin.
Arduino Mega boards can be connected to computers through USB connections and is powered by using battery or AC – DC adapter.
What is a Protoshield?
The ProtoShield is one of many Arduino shields. A Prototyping Shield is made to facilitate prototyping, it simplifies designing custom circuits. You can custom your project by soldering parts to the prototyping area. You can also use solderless breadboards to test circuit ideas prior to soldering. The ProtoShield creates easy connections between a breadboard and an Arduino.
Arduino Mega ProtoShield
The Arduino MEGA 2560 is used for projects that need extensive RAM, I/O lines, and sketch memory. Its recommended use is 3D printers and robotics projects as it has 54 digital I/O pins, 16 analog inputs and a larger space for your sketch. The Arduino Mega Proto Shield is an extra-large proto-shield, specifically designed to protect the Arduino Mega from potential damage or scratches from a new device.
The Arduino Mega Proto Shield casing placed on the Arduino Mega Circuit Board makes it easy to connect and control motors or for more complicated operation such as turning the PCB into a complex electronic device. The Arduino Mega Protoshield components are 2 buttons and a full set of extra-long, female stacking headers.
The Arduino Mega Proto Shield has extra connections for all of the Arduino MEGA I/O pins. It also has space to mount surface mount integrated and through-hole circuits, allowing you to turn your custom Arduino circuit into a single module.
Arduino Eagle Mega ProtoShield
Using AUTOCAD EAGLE design software you can custom your Arduino Mega Proto Shield easily and effectively.
What is EAGLE?
EAGLE is electronic design automation (EDA) software. It allows printed circuit board (PCB) designers connect PCB routing, component placement, and schematic diagrams. EAGLE has a comprehensive library content making it very easy for PCB designers to use. It only supports 64-bit operating systems, a minimum graphics resolution of 1024×768 pixels and a 3-button wheel mouse. Autodesk EAGLE works well with the following operating systems:
- Microsoft® Windows® 7 or newer is required.
- Linux® based on kernel 2.6 for Intel computers, X11 with a minimum color depth of 8 bpp, the following runtime libraries: libssl.so.1.0.0, libcrypto.so.1.0.0, and CUPS for printing.
- Apple® Mac OS® X version 10.10 or above for Intel computers.
Using AUTOCAD EAGLE for Arduino Mega Shield
The Arduino library has 12 variants, including the mega. Converting any design into the EAGLE Arduino Mega Shield library is not difficult. The following steps should help. While creating the design the first thing you may need to do is remove everything except for the board outline and connectors. Using a Designblock may seem easier, but creating a library is always better.
- Load the schematic from the EAGLE schematic editor.
- Select on File/Export/Libraries and choose the option of “merge into one library” to customize the library with all your components.
- Using design blocks saves the complete schematic and the board layout into the library.
- Choose File/Save as Design Block from the schematic editor to select the entire schematic and board file as a Block.
- Upload your project and click on Add a Design Block to display a list of blocks you can choose from.
- Click on the block you created a few minutes ago from the Arduino Shield.
You may have to draw in the pads at the correct locations for the board, and create a symbol for the board template and map as a device. This allows you to include the template in the schematic and design your shield or cape around that. By default EAGLE Arduino Mega Shield design program has a standard set of layers for diverse purposes and these should not be removed in the general case. Since the Arduino mega is a two layer board, the AUTOCAD Eagle template will appear as such.
Remember Arduino shields translate hardware complexity and simplify it into an easy to use interface. In doing so, you are able to design and implement your idea fast. The Arduino shield programming libraries easily integrate hardware features available on the shield. This should help you design your EAGLE Arduino Mega ProtoType Shield. All the best.