The Arduino is a small microcontroller board based on the Atmel ATmega168. By designing programming software “mated” to the board, and a simple IDE, the Arduino’s designers hope to make it more accessible to creative people who might otherwise find microcontrollers beyond their grasp.

Several variants of the board are available. The designers of the Arduino want that name to refer to the original; but since they make the reference design available, and encourage people to make their own (and sell them if they like), variants abound. The Arduino policy is that anything called “Arduino” should be, functionally and physically, a drop-in replacement; variant designs are allowed & encouraged as long as their name isn’t Arduino.

Most (maybe all?) of the variants leave off the USB interface and connector, to save cost & space and to make the boards easier to build – most variants are sold as kits, and the small, surface-mount USB chip is difficult to solder. For many applications the USB interface is used only to download the code, so having USB hardware on the board is deemed a “waste”.

Using a board that lacks USB requires a USB-to-serial cable. Of course, one can use one cable with several boards – just not all at once!

At this writing (2007 Nov) “true” Arduinos with USB cost about $33 (assembled); kits for USBless boards cost about $15; and the cable costs about $20. For a project that doesn’t require USB, but requires several boards, USBless can be much cheaper.

Two variants that seem intriguing are:

Of the two I have a mild preference for the Bare Bones Board – but no experience with either to inform this prejudice. ;-) The reason? There are two: when the Boarduino is plugged into a breadboard, it straddles the center, just as a large (say DIP40) chip would. This means that connections can be made on both sides of the board, but anything more than a connection to Vcc or Gnd must be made “to the side”.

The Bare Bones Board, like the Boarduino, can be fitted with male headers on the bottom, but it can plug into the top of a breadboard, leaving the whole space beneath it – both sides of the “gutter” – to build a circuit. There is a downside though: not all the connections (the analog inputs in particular) come out to this header.

However, that leads to the other seeming advantage: the analog inputs are arranged in a block of three by six header pins. There are six analog inputs; for each there is a trio of pins: Vcc, Gnd, Ain. Thus it is easy to fashion a cable that goes off-board carrying these three “signals” to a sensor. This seems like quite a nice design detail. On other boards – including the original Arduino – one must find power and ground elsewhere.

Another interesting board with about the same power, and at about the same cost, but that includes USB (it’s built-in to the microcontroller, unlike on the Arduino, where the USB interface is a separate chip), is the PIC18-based USB Bit Whacker.

I’ve found a few other USB development boards as well.