Arduino: Boards and modules are microcontrollers that are Open Source designed and Italian high quality made!.
They're made entirely from off-the shelf components, this means that you can download the plans, buy the components, and assemble your own with no legal implications. It just cannot bear the name Arduino since that is proprietary. You can use them, market them, sell them and that is all perfectly fine. Or to simplify your life, you can buy them fully assembled and ready to tackle your great idea.
So, what’s the big idea behind it? Previously if you wanted to build an electronic project it would require that you go to school and earn an engineering degree to learn how to assemble the components. Now in the Arduino environment you don't need to learn to program in a complex language like C, but rather get to use a simplified instruction set.
What makes the Arduino so special is the simple hardware, the simple programming, and a supportive community that surrounds it. In an open source environment people are willing to share their ideas and help others reach solutions to problems.
The Arduino is probably best thought of as a rapid-prototyping tool that can be used by people that don't possess a vast electronic or programming skill set. By mastering some very simple instructions it becomes possible to make devices perform very complex functions.
Arduino boards come in several flavors but for simplicity we’ll confine ourselves to the UNO. It has a USB interface for programming, a plug for an external power supply, a power regulator, a microcontroller chip, 6 analog input pins, a reset button, 12 digital I/O pins, 3 grounds (one digital), two pins for serial transmit and receive that are slaved to two LEDs, an LED to indicate that the unit is powered, and one LED that is specifically slaved to pin 13 on the digital side. It also has a crystal to act as an oscillator or timer. Six of the digital pins are capable of a simulated variable output to emulate an analog output by changing their state from 0 to 1 rapidly so that an LED may be dimmed for example.
Of course it doesn’t just end with the board. Since it has a standardized design it is simple to stack boards. However, there is a potential problem with multistacking shields. One of the most popular choices is to add an Ethernet/SD card shield to give you Internet access and provide additional storage space. Unfortunately the RJ45 port is so tall and jacketed in metal that it can short out the electrical traces on the shield above. The secret to solving this problem is to keep some stacking headers (as pictured) to give the needed clearance.
Other things you can add include speakers, onboard power supplies, motorized wheelbases for robots, joystick controllers for steering robots, segmented digital readout LEDs, LCD screens, motion sensors, motor controllers, OLED screens, and a completely crazy variety of different alternatives.
Bear in mind that the 3.3 volt power header on the card can only supply 50 milliamps, and the five volt power header is limited to 500 milliamps. As well, when stacking shields, there may be occasions where the pin-usage conflicts. You’ll have to learn to program around that. Another problem that might crop up is electrical noise such as a motor controller shield right next to a DAC (Digital-Analog Controller) shield. Keep them reasonably far apart.
People have been doing some amazing things with Arduino microcontrollers. They have built their own 3D printers, driven auto articulated bat wings and exoskeletons for their cosplay costumes, built plant monitors that automatically water your vegetation, created LED art displays, designed cat feeders where a particular dish will only open when the correct cat with an RFID collar approaches, all the way up to designing their own satellite which will be launched into space and available for people to perform their own experiments on a time available basis.
The future is in your hands. You no longer have to be a genius programmer, electronics engineer, or a millionaire to create the next great thing. All you need is a good idea...