Microphones

As several of you are aware, we are developing new Bluetooth hardware to add a functional microphone circuit, DSP capability, and an isolating amplifier to cut ground loop noise in the audio ground. We thought that the old board’s mic circuit wasn’t functioning right, so we’ve never sold the HFP capability. I have wanted to use the OEM mic location and wiring to the moonroof switch area, but it’s a 3 wire connection, of which I was trying to get working with 2 wires, Mic + & -. We were getting clicking/popping noises out of the microphone, so we assumed that there was something wrong with the bias circuit or ground, and went down that track trying to solve some issues there we thought were contributing to the noise. We got the new hardware back about a week ago, and have been doing some testing and I was initially disappointed to be getting similar performance with popping. On a whim, I connected the third wire (identified as a shield ground on BMW’s schematics) to the ground on the existing board, and all of a sudden the popping noises were 90% gone – I guess that circuit really needs that shielding. It looks like the bias circuit on the existing hardware isn’t the major issue, although I like the new bias circuit a bit better.

There’s always improvements that can be made to this board, as it is a much more complex and expensive adapter than our aux input CD changer emulator board. We have some adjustments to the cap values for the isolating amplifier so we don’t get as much of a high pass frequency response, some changes we need to make the board more producible, and firmware changes to accommodate a much better microcontroller. For those of you who’ve bought (or are interested in buying) the existing current bluetooth modules, we may be able to offer a reprogram service to provide some basic HFP support, although the circuit might be a little rough, and we can’t guarantee great voice quality. We’d like to get the hardware to a point where we CAN deliver very good HFP support.

We know many of you have asked us me for updates on the HFP capable modules, and I’ll let you know that we do need to make some changes to the circuit board which may take a couple more weeks depending on our work load here. We want to get it right for you guys!

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