Bela Gem Multi (&possibly stereo) MICBIAS access

Rick

Hi,

I'm trying to use electret microphones with the Bela Gem Multi through the AUDIO ports. I would like to bias with a 3.3V signal, Ideally, I'd use a clean low noise reference. I found that audio channels 3-10 use TLV320ADC3140 codec, and from its spec sheet there is listed a MICBIAS. Could anyone tell me whether the MICBIAS is accessible? Is it broken out to the extension wing for example?

Edit: Or, have I missed something and is biasing done automatically through the 3.5mm jack?

Thanks in advance, Rick.

giuliomoro

No automatic biasing, but there are pins labelled "MB" on the input wing where the mic bias signal is broken out for your use. You'll notice that there are 4 2x1 socket headers behind each jack, which are wired in parallel with the jack. If you are plugging the microphones via the jack socket, you can use a THT 1k resistor from the MB pins to the 2x1 sockets to perform the biasing without soldering.