[Bogdan] received this set of Serioux Panda speakers as a gift. I turns out that they sound very good and he decided to make them more useful to him by converting them to work as Bluetooth speakers.
To begin with he bought the cheapest A2DP device he could find. This is the protocol that identifies a Bluetooth audio device. The unit is designed to provide a Bluetooth connection for a set of headphones. He patched into the headphone port on that board, but also wanted to keep the option of using the Panda speakers’ line-in. To do this he added a 1k resistor to each of the audio channels. A connection was made from the 5V rail of the speakers to power the Bluetooth module rather than leaving it with its own battery.
Speaking of batteries, the Panda speakers can run from three AAA cells. This battery compartment was a perfect place to mount the add-on hardware. But the speaker can still be powered from a USB connector. Above [Bogdan] is using a portable USB power supply.