Electret Microphone Reading

I have been reading a book called Arduino Workshop, and just got to a point in the book where I thought I could create a project on my own with only using datasheets, but I am having issues. The type of project that I want to create is a simple clapper, you clap and it toggles an led. My problem lies with trying to get the microphone to read noise. I have attached a copy of the circuit using fritzing to this post. The electret microphone that I am using is Electret Microphone - COM-08635 - SparkFun Electronics(datasheet). To amplify the signal I am using a BD139 amplifier(datasheet).

I can get a reading from the microphone, however it only displays random values, and does not respond to any type of noise at all. I have also noticed that it slowly counts to 0 in the serial monitor when viewing its output, but I can never get it to go back up. Can someone please point me in the right direction, I was hoping this would be simple.

See: http://www.learningaboutelectronics.com/Articles/Sound-detector-circuit.php

[u]This microphone board[/u] would make things easier! It has a built-in amplifier and is ready to go.

Note that the output is biased at 2.5V, which allows the Arduino to read the positive & negative halves of the audio waveform. That's probably not important for what you're trying to do, but you need to know that "silence" will read about 512 on the ADC. When there is sound, you'll get "random" readings above & below 512, with louder sounds giving some higher & lower readings (perhaps closer to 1023 and zero).

In case it's not clear, the negative half of the waveform gives readings below the 512 mid-point. And, the readings seem random because if you are not using a sample-rate clock you are reading at random points on an varying AC waveform... like trying to read the depth of the ocean when there are waves causing your depth readings to jump around... Like trying the read the depth of the ocean when there are waves...

...I am using a BD139 amplifier(datasheet).

I can get a reading from the microphone, however it only displays random values, and does not respond to any type of noise at all. I have also noticed that it slowly counts to 0...

A transistor and a resistor is not quite enough to make an amplifier. And, electret microphones require power. In the link Larry gave you, power is supplied through R1, which is connected to 5V. The resistor is required because if the mic was "shorted" to 5V, the audio signal would be shorted-out. Capacitor C1 blocks that DC power from getting-into the amplifier input, but it lets the AC signal through.

LarryD thank you for that link it was very helpful. I may go check my local RadioShack for one this afternoon, and try and use it. DVDdoug, thank you very much for the helpful description, it helped me see where I was going wrong with the circuit. Even though I am going to try and get an lm386 today, I will most definitely get that microphone board that you recommended so that future products will be a little bit easier.