In final form, a Bluetooth module and Arduino Pro Micro are stuffed inside the stereo along with a DPDT relay to switch the I2C bus.

We’ve had very few car radios from scratch here at Hackaday, but we have had more than one bluetooth upgrade or addition of a line-in port. Thanks [Darkspr1te] for the story.

Your robot army, controlled by Arduino and Bluetooth Open-source hardware project shrinks Arduino, adds wireless, creates awesome.

Primo will include Bluetooth LE (low energy), NFC, Wi-Fi, and infrared built-in — you typically need a “shield” add-on to get these features.