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Feb 05, 2017, 02:39 AM
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Another vehicle speaker

Congrats to the guy who got the last of the $10 Vivitars. That made the rest of us losers, even if $18 was equivalent to a single commute. Paying more than someone else for the same thing is still losing. $18 later, the 2nd bluetooth speaker arrived, with the goal of a robot speaker & job interview headset. It has become essential over the years for every vehicle to have sound & for it to be wireless.

It was quite loud & was probably light enough to use intact. The mane interest was hacking it to also take a microphone input. The innards revealed a 350mAh battery. 350mAh batteries have been revealed to last 30 minutes. It would have to be upgraded to support a full drive.

Most of it was a big, heavy speaker brick which can't be opened. It weighs 150g, which is the same as any other speaker. New speaker technology is needed if the same loudness is going to get any lighter.

Connectivity uses a very old BK8000L board. It uses a PN25F04 flash chip to store firmware. Audio amplification comes from an HT6871 3W class D mono amplifier. The positive stereo outputs of the BK8000L go through a pair of R + C's. The outputs of the 2 C's are tied together before feeding the amplifier's positive input.

An overly aggressive standby mode wipes out all transients, so it can't play game sound effects or metronome sounds unless something is always playing in the background.

Volume down is floating. Volume up is pulled to Vbat by a 10k, so the volume is fixed to an unknown default. There are serial port commands for tweeking the end user settings but not setting the bluetooth name. The microphone input is disabled in the firmware. They disable the microphone & set the bluetooth name by bit banging GPIOS 2 & 3. This part of the configuration is unavailable to the public, to prevent someone from reselling the speakers under a different brand.

The job interview headset is probably only viable with a windows PC anyway, since bluetooth microphone input on the Macbook never worked. It takes much begging just to get the macbook to play output through it.
Last edited by Jack Crossfire; Feb 05, 2017 at 03:04 AM.
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