DTMF decoder test circuit circuit board

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. Video

The built circuit is straight out of the datasheet on page 15.

DTMF decoder schematic

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.