Hi All,

I know that there are some electronic experts out there in this community and so I need your help. What I'm working on is a digital recording system. Here is how I layout the project and what I need help on.

Part 1

The analog input part: Using an electret microphone, I need to amplify the sound signal and send it to an ADC on the MCU. Problem: I do not know how to hook up an electret microphone to a transistor amplifier. I do knon the basic operation of an amplifier though. Also know how ADC works too.

Part 2

Digital recording from ADC: Using the ADC, convert the input sound signal into digital data and store it in an EEPROM. Problem: This digital part is easy. I can handle the writing/reading to/from an EEPROM through SPI/I2C.

Part 3

Sound Playback: Read the sound data stored in the EEPROM and convert it back to sound wave using PWM and output it to a speaker. Problem: I know how PWM work but I do know know how to hook this to an output speaker.

Summary

Now you sort of get an idea of what I'm trying to do. As you can see, Part 1 and 3 require analog knowledge and Part 2 is all digital. I'm good at digital electronic but when it comes to analog, I'm weak. So really, I think what I need help on is just the analog stuff.

A tutorial/circuit showing just part 1 and 3 would be awesome. For example, taking the sound signal from an electret mic, amplify it, then send it out to a 2Watt speaker. If I can do that, then I can integrate the digital part in between the input and output and complete my digital recording system.

I think this project is very good for other people in this community to learn because it's a combination of both analog and digital. Any help is appreciated and thanks in advance.

By the way, for the amplifier, please no fancy IC chip. For learning purpose, I want to use a transistor or an op-amp do the the amplification then send the signal to the ADC on the netduino. I have all the equipment to test/debug such as an oscilloscope and logic analyzer. Thanks all!!

xc2rx