voltage What kind of Mic do I need to connect to a pots telephone line to speak

What kind of microphone or mouthpiece I can use to connect across a pots telephone line in order to send dtmf tones ( no voice ) dtmf only. Can I use a regular mic or does it have to be a certain type, I am using a 300 ohm resistor to hold open the line automatic and I need to know what kind of mic i need or if i will need any

additional components to make this work thanks Back in the stone ages a telephone used a carbon microphone (300 Ohm IIRC). This page rane. com/note150. html shows the signal level as 275 mV, but I am not sure whether that refers to the incoming or outgoing signal (or maybe to both ) Wouter van Ooijen Apr 10 `13 at 18:37

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