For that, I needed Serial communication within ruby. Thanks to ruby-serialport first steps went quite well. I could write OR read from and to Arduino easily. But for some reasons, writing AND reading using the same instance didn’t work out.

I used a simple ‘send-input-back’ sketch on the Arduino side. So every byte I’m sending is returned back. I checked with the Arduino IDE Serialmonitor and a simple Processing script – everything worked alright. But using ruby it was different. Writing to serial port worked okay, but reading from it was just random. Sometimes I read the response, sometime I didn’t – really, really weird. Some headaches and a lot of time testing I finally found the solution: just open two instances of the serial port. One for sending, one for reading – and, surprise, surprise – it works perfect! Who would have guessed that!? Strange..

// To be completed
require 'serialport'
port_write = Serialport.new()
port_read = Serialport.new()

Ok, continuing hacking, more soon…

The first real basic problem I ran into was how to program the Rainbowduino as there’s no USB connector and I don’t have an UART interface.
But well, nothing simpler than that: Just connect your Arduino’s Tx,Rx,GND,Reset and Vcc ports with those of the Rainbowduino, choose the right controller type in your IDE and program it as usual – works perfect for me!

Check out my Rainbowduino Editor mtXcontrol here – it’s an easy way to draw shapes on your rainbowduino!

Btw. DTR on Rainbowduino is Reset on Arduino

UPDATE:
Sorry I forgot to mention, this trick does NOT work if your host arduino is a ATmega168 – you need an ATmega328 to pass serial communication through. Before that, make sure you upload this blank sketch to your host Arduino first:

/* blank sketch to upload on Arduino */
void setup()
{
}

void loop()
{
}

And, as multiple times requested, a picture of my complete setup:

Make sure you’ve selected the switch right. It has to point to the same side as the green Terminal connectors are. If you power rainbowduino through the white JST jack, flip it!