HOPEX I have been cramming about electronics design. I have been positively obsessing over development kits of all kinds.
Three wonderful objects of technolust are the Arduino, the Raspberry Pi & the BeagleBone Black.
That list is in chronological order, order of complexity as well as increasing price order.
They are all roughly the footprint of a credit card & they are all extremely inexpensive.
The Arduino is essentially an embedded processor on a breakout board. You connect to it from an external computer & upload software to it - referred to as "sketches" instead of 'programs' for some reason I still don't understand. As a development kit it is very forgiving and flexible. This has been the darling of the Maker/Hacker community for embedding logic in all kinds of things.
The Raspberry Pi is a full-blown computer that runs Linux, has USB ports, Ethernet, and video output. It boots from an SD card. You can actually use a Raspberry Pi to program an Arduino - and many people combine the two - though to be honest I'm not sure that I understand the advantage to this beyond having an inexpensive computer dedicated to the function. Embedding both into a device seems unnecessary... The Raspberry Pi was invented to fill the need of providing students with a low-level understanding of how computers work. My generation had Apple //e computers to fill that niche.
The BeagleBone is similar to the Raspberry Pi in that it is a standalone computer. The BeagleBoard and BeagleBoard XE were predecessors that cost >$140 and managed to generate very little interest. The newer, stripped down BeagleBone Black is much closer to the price point of a Raspberry Pi. The BeagleBone Black however has far superior specifications than the Raspberry Pi and the design is completely open source, right down to the core hardware.
For under $200 you can easily own the latest & greatest versions of all 3 devcies & still have money left over for accessories. If you look at the picture you will notice lots of pins on the sides of the boards - these are designed for tinkering! Have at it.