Diana Eng and I hacked a Star Trek (TOS, thank you) communicator toy, making it into a bluetooth speakerphone for use with a cell phone. You can read about it at makezine.com.
We made a few minor enhancements since the article was first published, most notably adding an LM4890 audio power amplifier to get more volume from the speaker. Here is the updated schematic:
You can download the sourcecode and schematic here: toscomm.zip.
Note that recent versions of avr-binutils have a small incompatability with the Makefile used in this project. The problem, and two possible fixes, are described on this thread on avrfreaks.
Also note that the schematic diagram shows a MEGA16 microcontroller, whereas the device was actually built with a MEGA168. I used a MEGA16 in the schematic because my Eagle library didn't have a MEGA168 part, and the MEGA16 was the closest I could find. The parts are similar, but the pin numbering is different, so don't try to just blindly connect things up based on the pin numbers. You need to connect components based on the labels, e.g. TXD and RXD to the bluetooth module, SCK, MISO, and MOSI to the DAC, XTAL1, XTAL2 to the crystal, PB0, PB1, and PD7 to the LEDs, etc.
Read more at Gizmodo, Engadget, Bluetooth SIG
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