[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.
By using the 1k resistors, he basically used it to sum/mix the two signals, bluetooth and line in. Otherwise the better option would be a 5 pin headphone plug, that physically switches signals based on if a 3.5mm jack is plugged in or not.
Exactly, the signals are summed.
The panda has a small cable that wraps around and can be stored, ending in a 3.5mm connector. I thought it was better to sum the signals than to replace the cable with a female connector on the panda and require to carry another cable with me.
The mix is simpler and cheaper. I want to set up a friend’s TV audio to work that way. He doesn’t want to switch anything more than he has to already, DVD ATSC tuner etc. I want to add radio and his standalone XM radio to the mix, in to a real sound setup. Since it’s easy to turn on and off equipment, just mix at the right levels all sources. The only caveat is turn on thumps, but most gear has delayed mute stuff inside. He is not a purist by any means, there maybe residual hum etc. Nobody can be a purist with a bluetooth stereo feed or worst of all such target practice stock as that tempting watermelon. Broadsword or bullets, or how about air launched (it’s aerodynamic) let me at it. Skeet-er shoot!