I have a Sony STR-DE845 home theater amplifier with 8 Ohm speakers. I want to measure the voltage sent to the speakers to infer their volume using an Arduino. The AC voltage measured across a speaker ranges from 20mV to 180mV using a true RMS voltmeter when playing music or various test tones over the audible volume range (are those readings too low?).
To do this I want to: -amplify the AC signal with a gain of ~100 (output is 2VRMS to 18VRMS) -put the amplifier signal through a full bridge rectifier made of 1N4148's (output is ~0V to 16VDC) -Use a voltage divider and zener diode to give ~0 to 5V DC for the arduino's analog pin
If the above makes sense, what kind of circuit should I use to amplify the AC signal by 100? I have some AD623 instrumentation amplifiers, 2N2222 transistors, 1N4148 diodes, etc.