The MT8870 is a common DTMF decoder, it uses an audio-in signal. Here is the common schematic:
http://www.qsl.net/oe3mzc/mt8870.gif
Some of the values vary a bit depending on the schematic but the basics are the same.
However, I want to use an electret microphone as the input audio source. What kind of amplifier circuit do I need to put in between the electret microphone and that circuit above? Thanks!
http://www.qsl.net/oe3mzc/mt8870.gif
Some of the values vary a bit depending on the schematic but the basics are the same.
However, I want to use an electret microphone as the input audio source. What kind of amplifier circuit do I need to put in between the electret microphone and that circuit above? Thanks!