Several times we received questions about how to hook up a flight
helmet and mask/boom mike to the Personal Computer. Especially
the die-hard flightsimmers like to hook up the real gear to their virtual world. Therefore I decided to write an article about how to make an adapter
cable for this purpose.
The most commonly used
earphones in military flightgear is the H-143 model earphone. The earphones are wired in
parallel which gives a total impedance of 8 ohms. The biggest disadvantage of this system
is that the sound produced by the earphones are Mono because both earphones receive the
same signals. Also the quality of the earphone elements are good for communications but
don't give a Hi-Fi quality.
Another problem is the signal
coming from the microphone. This signal is very weak and should be amplified. You will
also find a very simple but working microphone amplifier schematic which will improve the
signal of the helmet microphone so it can be used in combination with the PC.
OK, lets get started! First we
need to know what materials we need to built this adapter.
2x mini-jack, mono
(this are the mini jack plugs what goes into your PC soundcard but in mono instead of the
stereo version which is commonly used. Difference is that the mono version only have two
rings instead of the three rings)
(don't use to thick wires, 20AWG is good enough)
(or similar, see drawing below. This plug fits the U-174/U or U-93A/U plug which is
commonly used at flight helmet and oxygen mask commcords)
I have done some measurements
on the U174/U plug on one of my helmets. I have made following conclusion:
The contact numbers are
corresponding to the numbers of the solder contacts in the U-92A/U plug.
With this information we're
able to make the adapter cord:
Cut two pieces of speaker
cable of the same length (length you prefer) and solder both of the mini-jacks on one end
of each cable.
Now you have two dual wires,
both with one plug. Mark one of these cables on both ends with a marker or a piece of
tape. Just for recognition which cable is for what.
Solder the microphone wires
on the contacts of the U-92A/U plug. Ground on 3 and + on 1
solder the earphone wires on
the contacts of the U-92A/U plug. Ground on 4 and + on 2
Now you have an adapter cord
with an U-92A/U plug which fits your helmet with two dual wire cables coming out. At the
other end the two jack plugs which fits the soundcard of your PC.
To Amplify the microphone
signal you need to place a small amplifier in the mic.line (contacts 2 and 4 in the
U-92A/U plug). The schematic below shows a simple but working amplifier. The amplifier
works between 6 and 12 Volt so a simple 9Volts battery will work. I don't have done tests
to this design but it seems to work.
The parts list for this low-cost amplifier:
1x BC548 NPN transistor
1x BC558 PNP transistor
Resistors (0.25W 5%)
1x 100 Ohm
3x 2.2 kOhm
1x 22 kOhm
1x 10 kOhm
2x 100 kOhm
1x 150 kOhm
1x 0.1 microF MKT Polyesther
1x 1500 pF MKT Polyesther
2x 10 microF Electrolytic capacitor
1x 22 microF Electrolytic capacitor
1x 100 microF Electrolytic capacitor
If you have further
questions or suggestions, please contact me by sending an e-mail to firstname.lastname@example.org