Then Q23 turns ON, Q6 and Q8 also turn ON accordingly. As you can see from the circuit of the IC-HM9 speaker-microphone, if you push the PTT button, the base of Q23 will be connected to GND through R55 and the 33kΩ resistor in the IC-HM9. Connect the speaker-microphone plug here. On the left of Figure 4 you can find the jack terminals labeled EXT MIC and EXT SP. 3 IC-HM9 circuit diagram What is happening inside the radio, beyond the microphone plug The speaker part drawn on the top is omitted, but the microphone and the PTT parts are still working with only two cables.įigure. 3 shows the circuit diagram drawn with the disassembled IC-HM9. 2 Circuit diagram for independently operating the microphone and PTT Drawing a circuit diagram with a disassembled IC-HM9įigure. However, in reality, there is only one monaural plug, so two wires are sufficient.įigure. The schematic diagram is shown in Figure 2 below. Normally, when trying to make two functions work independently, a total of three independent wires are required, one for each function, plus the wire for the common ground (GND). These two features are connected to a 2.5 mm plug. The challenge is two functions (2) and (3). The speaker has two independent wires connected to a 3.5 mm plug, so the speaker function is excluded here. The two types of speaker-microphones, such as the IC-HM9 and HM-131L listed above, have the following three functions. Now I would like to explain the mechanism. 1 IC-HM9 and HM-131L The mystery of working a microphone and PTT with two wires However, that any speaker-microphone can be used with either monaural or stereo type plugs.įigure. It seems that the speaker-microphone plug has changed from a monaural to a stereo type during the company's product development.
Looking at the IC-HM9 plug, both the speaker plug and the microphone plug are the same monaural plug. The IC-HM9 was an option for that transceiver, but its microphone plug, unlike the recent speaker-microphones, had a monaural type plug. 1) There was an IC-2A series handheld transceiver that was popular around 1980. These days, Icom's speaker-microphones for handheld transceivers have a monaural type plug for the speaker and a stereo type plug for the microphone.
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