I’ve got an RN-52 (on the breakout board and 3 more without it) and I’m trying to get an electret working decently well with it. The RN-52 is being powered by a small LiPo battery (3.7V nominal) and everything is working fine (speakers stream audio, mic even works…kinda).
The issue is that the audio from the mic has a ton of noise (terrible SNR) and is almost unusable. While monitoring the audio on my PC, I’ve found that powering the electret circuit from the same battery that the RN-52 is connected to sounds great even while the RN-52 is powered on and connected to my phone. However, as soon as I start one of the Bluetooth profiles like by streaming audio or making a call through the RN-52, the noise gets crazy high (so I presume the RN-52 is doing something wonky to the voltage there when it is really doing stuff).
I’m not sure if my diagram got uploaded, but I’m basically running the RN-52 3.3V pin (also connected straight to LiPo) to the electret ‘+’ side through a 10kOhm resistor and the RN-52 GND directly to the electret ‘-’ side. Then I run GND to Mic L- and Mic L+ gets connected to the electret ‘+’ side through a 100 nF capacitor. Again, sounds terrible once the RN-52 actually does something useful.
So then I tried powering the electret mic through a separate 3V supply (two CR2032s) and when connected in the same way to the RN-52 (only Mic L- now connected to the GND on the CR2032s), I can get audio to come through the RN-52 clearly (as in during a phone call). I’ve had little success using M_Bias to power the mic and I’m wondering if that is because the audio ground pin is not exposed in the breakout.
Is there something I should be doing with the bias or something to “clean up” the battery voltage when the RN-52 is working. I don’t have an oscilloscope or anything to test, so I feel like I’m kind of in the dark right now. I really would like to get the mic on the same battery supply as the RN-52. I also have the MEMS breakout and the 3-pin electret breakout if those would be better to use, but I’d rather get this working with a regular electret mic.
