I am developing a prototype device, that shall perform the following tasks:
- Record a voice sample while a switch is pressed and held down
- Save the voice sample on a microSD card
- Load and playback the voice sample when a PIR sensor is triggered
I am using an ATmega 644PA (44PIN TQFP). The whole circuit is powered by a 3.3V coin cell battery.
My microphone is a standard Electret 34dB. I have various speakers I will test with, from 1W/4Ω to 2W/8Ω.
- Because I only have 3.3V, I can't use the LM386 OpAmp to amplify the audio signal. Is this general purpose amplifier a reasonable substitute?
- What is the best practice: To amplify the audio signal when recording, when playing back, or both?
Any input much appreciated.