8051 C code for ICOM HM-133 and HM-151 Microphone DTMF adapter This project allows an HM-133 or HM-151 digital microphone to produce analog DTMF tones and thus connect to an older transciever, or any new transceiver that accepts an analog modulation input. See https://ke0ff.github.io/hm133/index.html for project hardware details.