We are going to start with our cheapest and tiniest computer, the Arduino Nano.
If you buy one from a local store, you might find them for $10 or $15. Buying from an Internet store that can get one to you quickly in the mail might cost you $7. Buying directly from China using AliExpress, you can get one for as little as $2.52 as of the time we are writing this. For your first one, you will want to pay another fifty cents or so for the USB cable it needs. But the one cable can be used for any number of Nanos.
This tiny computer is 45 millimeters long and 18 millimeters wide (1.7 inches by .7 inches). The computer is in the middle of the photo. Those other things are optional. They can be soldered to the board to make it easy to connect things later without soldering.
Later on we will show you how to build devices using a single computer chip, rather than the Nano board (which has several chips on it). That will be especially useful for battery or solar powered projects, since the extra chips on the Nano use power even when they aren't being used. But for most of the projects, that little extra power won't matter, and the convenience of the Nano will make things come together quickly.
Our tiny little computer has no keyboard and no screen. We program it by connecting it to a desktop or laptop computer using the USB cable.
The software needed to program the Nano is free. You can download it from the Arduino web site, and install it on a WIndows, Macintosh, or Linux-based computer. If you are using a Raspberry Pi as your main computer (a $35 tiny computer itself), the Arduino software is already loaded and ready.
When the software is downloaded, installed, and run, the first screen looks something like this:
To set up our Nano, we need to select Arduino Nano in the Board menu:
Next, we tell it which port our Nano is on:
If it is not clear which port to use, look at the list (write it down if needed), and then unplug your Nano and look at the list again. The port to use is the one that does not show up when the Nano is unplugged.
Once the board and port are selected, we are ready to program our tiny computer.