The intent here is to provide some background on what the Raspberry Pi is and why it came into existence. Knowing what you're dealing with is always helpful.
It is important to remember some of the original motivations that brought the Raspberry Pi into existence. It was not akin to a company like Apple thinking up a cool glittery new product like an iPhone and then making and selling it. Instead, it was created by a relatively small group of people to help solve a perceived problem - the lack of an easily available computing device that people could use to gain direct hands on experience without spending a small fortune.
This led a computer scientist from Cambridge by the name of Eben Upton to try and create such a device. The story spans over many years and involved numerous contributors. It is worth hearing the whole thing:
In a simple quote, the motivation comes done to:
"We need to create a generation of producers not consumers."
Ebon Upton, 2013, Wired
Consumers buy and use smartphones. Producers actually make the smartphones - and all the other techy goodness in our future world. There are lots of exciting technical details to learn. Basic electronics, I2C, SPI, and other interfaces, software to drive it all, etc. It's essentially a journey of learning that never ends. Having a relatively cheap and easy to access device helps bootstrap this journey.
A key point in the requirements for the Raspberry Pi was that it cost only $25. This was to make it reasonably cheap to acquire. But also, the creators of the Raspberry Pi knew there was going to be a high potential for damaging the boards in the process of playing around with them. So they also did not want it be a large amount of money lost when the blue smoke monster showed up.
This price point was met. The original Model A was $25.
It is basically the brains taken out of a smartphone and put on a board that gives you direct access to a lot of the brain's functions. Think of it like this:
The real unique feature of the Raspberry Pi is the 2x20 row of header pins across the top. These are often referred to as the GPIO pins, or GPIO header, for General Purpose Input and Output. Those pins are directly connected to the brain. There's also a little heart - that's what provides power to the brain and everything else. It is also directly connected to the GPIO header in a few places.
So not only do you have direct access to the brain, you also have direct access to the heart. On other devices, like your smartphone, those connections are buried deep inside and you generally do not have access to them.
There's a bit of a double edged sword to the Raspberry Pi's GPIO header. By giving direct access to the brain, you can do all kinds of amazing things. You can even connect to the heart to help power those things. This is what the Raspberry PI was designed to allow you to do. However, there is no protection mechanism from damaging either the brain or the heart.
Don't let that prevent you from exploring what can be done. Simply understand this as the general nature of the way it is.
Read this guide for some general tips on how to care for your Raspberry Pi. Follow other guides carefully to make sure all connections are correct. And if you do somehow damage your Raspberry Pi, try not to get overly worried about it. It is never fun when this happens. But it is how we learn. And there is no substitute for the direct hands on experience you have gained.
No. But they are similar in that both provide you access to the brain taken out a device. Where the Raspberry Pi brain was taken from something like a smartphone, Arduino brains are more like what you would find in a microwave oven. They are intended for doing small simple tasks really well. With a Raspberry Pi, there are thousands of these kinds of tasks going on in a complex dance.
So why not just us a Raspberry Pi for everything? Pi's cost from $5 to $35 and Arduino's have about the same price range. So what's the dif?
Consider the task of talking to NeoPixels. This is done by sending out a digital signal with a tight timing requirement. The signal has to go high/low/high/low etc. just right for the NeoPixels to work. An Arduino can do that really well, since it has nothing else to do. However, on a Raspberry Pi, there's network stuff going on, maybe a web server is running, oh, and now someone is printing something out, and someone else just logged in remotely, cron jobs to check, now someone started playing an MP3, etc. With all that going on, a Raspberry Pi has a difficult time maintaining the timing requirements for the NeoPixels. Getting NeoPixels to work on a Raspberry Pi has been accomplished, but via a complex work around. Using NeoPixels on an Arduino board is a simple matter of writing and uploading a program.
So...Arduino's are really good for doing one or a few things very precisely. That's important in a lot of applications. Like driving NeoPixels!