The HS34 has an audio output that can produce tones or voice output. This is a step up from a Dynon EFIS or EMS which can only produce a few tones of fixed frequency and volume. The audio output is located on pin 25 of the male connector on the HS34. The ground for this signal is the common aircraft ground.
The signal out from the HS34 should be roughly equal in volume to that of the Dynon EFIS or EMS. This generally means that when directly connected, it is louder than you want it and you must hook a potentiometer up between your HS34 and your intercom in order to adjust the volume. If you do find that the audio output is too loud, please wire a potentiometer as found in the EMS or EFIS install guide (such as Radio Shack Part #2711715). The HS34 audio is also the same as the EFIS or EMS audio output in that it must be run to an intercom and cannot drive a headset directly.
The output of voice or tone is a user option that is configured under the "HSI" option in the EFIS setup menu. Go to "Voice alerts" to edit these options. "Test on startup" allows you to choose whether you hear "Dynon Avionics" each time the HS34 boots or not. "EMS Alerts" and EFIS alerts" can be set individually to a tone or voice output.
When set to "tone," EMS alarms will generate approximately the same tone that they do today. There is a singular tone for all alarms that cause a tone, and the tone will persist until the silence button is pressed or all alarms are acknowledged. When set to "voice", the HS34 will output an English language annunciation of the actual problem. For example, if your first CHT goes above range, the HS34 will announce "CHT 1 High." This will only be announced once, but the alarm bar will persist on the screen until acknowledged. It is not possible to output a tone for some alarms and voice for others.
When set to "tone," the EFIS altitude alerter will generate approximately the same alternating tone that they do today. When set to "voice", the HS34 will output an English language annunciation of the climb or descend command. The climb or descend command will be repeated twice and then will not occur again until the alt alerter is re-armed via an adjustment or altitude change. The AoA alarm on the EFIS does not currently have a voice command. The audio will come out of the HS34 and will sound just as it does out of the EFIS today, with all adjustments in the AOAALM menu working as defined.
When the HS34 is connected, the original tones are still output by the EFIS and EMS. It is not suggested that you have the EFIS/EMS and HS34 hooked to the intercom at the same time, since this will cause the various audio signals to compete and interfere with one another.
Wiring with Stereo Intercoms
Common Experimental Intercoms allow a single music input in addition to radio inputs. Frequently, users want to be able to blend in an actual music source along with the audio alerts (Note: Most intercom music inputs suppress input by default when radio messages are being received. This example will also work on the radio input, but as it is not stereo anyway the standard documented wiring recommendations will work fine). The graphic below is an example of how to wire in more than one source so each has a separate volume control.
Special Kudos to Vern from Vx-Aviation for providing info on this...