Modern Device offers a couple of fantastic, low-cost, bare-bones Arduino-compatible boards and kits, called the BBB (Bare Bones Board) and the RBBB (Really Bare Bones Board). The BBB is larger (yet still 1/3 smaller than the ArduinoDuemilanove), and the RBBB is about the smallest and least expensive you can go with the full size ATMega168 or ATmega328 — great if you have limitations on space.
But with less space usually comes fewer components, so here’s a breakdown of what the BBB has specifically that the RBBB does not. You might find that the $13 RBBB kit is really all you need.
- ICSP Header – The RBBB does not have an in-circuit serial programmer header. This header is for directly programming the AVR MCU (microcontroller), rather than just loading up sketches. For example, you might use it to burn a bootloader onto a blank AVR chip. But if you’re happy with the Arduino environment, then you probably won’t need this; the chips often already have the bootloader installed.
- 0.1 uF Capacitor, Pin 21 – The capacitor is left off of the RBBB, but they recommend you add it externally.
- 10K Resistor, Pin 2 – This resistor lies between Pin 2 and the TxD pin on the USB-BUB or FTDI TTL-232R cable port. The purpose of this is to prevent something connected to the TxD pin (which is the chip’s RX line) from supplying enough current to actually power the microcontroller if it’s not powered on its own. So long as you’re using the whole cable port or are powering the board independently, the resistor isn’t necessary.
- 15uH Inductor and Capacitor, Pin 20 – Inductors help to smooth out current, and it’s really a nice-to-have rather than a must-have. The Arduino board itself doesn’t even include it.
- 1N400x Diode – This 1-amp power diode lies between the +5-12V power jack and ground, and prevents current from flowing through the entire circuit in the wrong direction. Wire your power carefully and you won’t need it.
- 0.1uF Capacitor – This is one of two bypass capacitors that sit between the power jack and ground just before the voltage regulator, and it’s missing on the RBBB. The larger capacitor is still there, though, and it helps smooth out the voltage coming in (e.g. filtering out electrical noise). The smaller capacitors are for smoothing smaller frequencies.
- Power Jumpers – The BBB has two 3-pin jumpers that allow you to configure its power source, and the RBBB omits these jumpers. The jumpers allow you to power either from USB or an external supply. A power rail supply can be passed through the regulator or not, or even used to power a breadboard if the main power comes from USB or the power jack. The RBBB is simpler, allowing you to power either from USB, or from the power jack, or (if the power is already regulated) directly to a power pin. If you already know how you’re going to power your device, you probably don’t need the flexibility provided by the BBB.
That’s it. Other than these things (and the obvious size and pin differences), the two boards are functionally identical.