DTMF Decoder Test Circuit

 As part of a few projects I'm working on, I want circuits to be able to decode DTMF tones played over an amateur radio link for remote control. This can be done with a moderately powerful processor in DSP, but I opted to buy a handful of MT8870D dedicated DTMF decoder chips on eBay.

I wired together a quick little test circuit, and it worked right away.

The built circuit is straight out of the datasheet on page 15.
I'm feeding audio into it from a GM300, which is a common commercial radio that with some effort you can get working on the amateur bands. I haven't done any testing yet as to how noise immune this DTMF decoder is, but I expect most of my remote control commands to be done with enough power that radio link noise won't go beyond the datasheet specs.

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