KRAPman
Newbie level 4
Hello!
I am working on one of my project embedding GSM module (SIM900). The dimension specs are very strict and everything is soldered on 2-layer PCB (dimension are only arround: 4.5x4.0 cm). My design also includes 2 electret microphones (2-pins mode like this: shematic). With one I would like to measure noise level in a room, so I amplify my electret's signal using external amplifier and connected its output to my ADC input on my MCU. I have done this using single-ended ADC, but I was getting huge noise spices coming from EMI radiation of near GSM module and antenna (no, I can not move the antenna nor the module more then a few cm away): spikes are from TDMA signal, generating 217 Hz noise. Then, I decided to go on differential inputs on my ATmega128A(ADC0 and ADC1, gain:200x), but now I do not know how to (phantom-)power my electret. I already have 1 electret connected to SIM900 module on pins MIC_P and MIC_N with GSM TDMA supressing capacitors on signal lines (which works great!) and now I like to duplicate a design like this on my ADC inputs on my Atmel. How can I do it? What would be best solution, i.e. best performance with low cost?
Thank you for any of your advises in advance!
Regards
Single-eded ADC GSM TDMA noise problem
How should I like to have my electret differentially connected to MCU
I am working on one of my project embedding GSM module (SIM900). The dimension specs are very strict and everything is soldered on 2-layer PCB (dimension are only arround: 4.5x4.0 cm). My design also includes 2 electret microphones (2-pins mode like this: shematic). With one I would like to measure noise level in a room, so I amplify my electret's signal using external amplifier and connected its output to my ADC input on my MCU. I have done this using single-ended ADC, but I was getting huge noise spices coming from EMI radiation of near GSM module and antenna (no, I can not move the antenna nor the module more then a few cm away): spikes are from TDMA signal, generating 217 Hz noise. Then, I decided to go on differential inputs on my ATmega128A(ADC0 and ADC1, gain:200x), but now I do not know how to (phantom-)power my electret. I already have 1 electret connected to SIM900 module on pins MIC_P and MIC_N with GSM TDMA supressing capacitors on signal lines (which works great!) and now I like to duplicate a design like this on my ADC inputs on my Atmel. How can I do it? What would be best solution, i.e. best performance with low cost?
Thank you for any of your advises in advance!
Regards
Single-eded ADC GSM TDMA noise problem
How should I like to have my electret differentially connected to MCU
