Hi I want to fix a circuit with a led. I need to use a transistor to play the role of the switch to the led.I want to switch on the led by playing a sound.I know I need a microphone connected to the base of the transistor. That is how far my knowledge goes.any help?? can this be done?and if yes how?any ideas are welcomed.thank you
Kyriakos

Connect a suitable supply voltage to the collector, and the LED to the emitter. Ground the LED to the ground of the supply voltage.

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Above is basically all you need , maybe a couple of resistors, and correct orientation of LED, Here is a more elaborate, expensive, time consuming project:
http://www.electronickits.com/kit/complete/elec/k-36.pdf