Back in the DOS days we were networking several computers to fly the Falcon 3 simulator and needed a way of communicating.
Apps like Teamspeak were not invented and even if it had been, it wouldn’t have worked since we needed over 600K of the 640K available to run the sim.
So we needed a hardware solution. I designed this and Christer Johansson made the PCB.

This is the original text that we published back in 1995, enjoy 🙂

SimCom(c) Mark I
Intercom for computer simulators

SimCom(c) is an intercom for computer (flight)simulators, suitable for all multiplayer games/simulators. It has a built in noise generator to simulate radio interference and It mixes your computers sound with your outgoing voice to simulate background sounds from your cockpit. It runs on battery (9V) or AC adapter (5-12VAC or /7-16VDC). You can connect several (we don’t now exactly how many, but 6 works fine) SimCom(c) on one or two twisted pair cables. It is made to enhance the realism of your simulation, so it’s defiantly no Hi-Fi quality sound. You can adjust the level of noise and interference from none to a level where it’s almost impossible to hear anybody.

SimCom(c) works in simplex mode, this means that while you press your PTT (push to talk) button you don’t hear anything from any of the other players, and while you don’t press it you hear all the other players that do press there PTT. It has two channels, one is typically for communicating with your wingman or RIO and the other are for the whole group. The PTT is a three position switch, spring loaded to the center position. In center position you receive all thats going on on both channels and the other positions are for sending on channel one or two.

SimCom(c) is shareware (probably the only hardware shareware ?) and you may distribute these files freely to bulletin boards and friends as long as the contents are not changed or altered in any way. If you decide to build it, all we ask is that you send us a postcard. If you send us US$10 we will E-mail you the PCB layout in HPGL and BMP format and the component placing in BMP format. If you prefer to, you can also buy it from us in different forms. If you send $20 we will mail you the PCB, the circuit board without components and without holes, add $10 if you want us to drill it for you. You can also buy the complete thing as a kit including headset or built and tested including headset, in both cases we do not include any box, casing or power supply, you will have to build it into a panel or something yourself. Contact us for prices.

We are not, and can not be held responsible for any damage or injury to any thing or person that might occur due to the use of or when building the SimCom(c). If you are not familiar with building this type of electronics, find someone that can do it for you. We can not guarantee the function for SimComs not build and tested by us.
Component list for SimCom(c) Mark I Rev.2

ELFA part no, for Scandinavians only.
No. Value ELFA nr. (ELFA alt.)

R1,2,9,17,18,22,23 10K
R3,4,14,15 1K
R5,6,16,19,20,21 820K
R7,12,13 100
R8 47
R10 470K
R11 18K
R24,25 8,2
R26,27 47K

C1 100n All cap. < 1u are polyester, => 1u are electrolite.
C2 22n All are standing vert. 2 modules, 5.08 mm (0.2″)
C3 4,7u
C4 1n
C5 470n
C8,9,11,12,13,19,22 100n
C6,14,15,20,21 1u
C7 2,2n
C10,18 10u
C16 47u
C17 470u/25V 67-009-34

P1 220K Horiz. Trim, Mic gain 64-363-03 64-371-07
P2 50K Horiz. Trim, Noise level 64-362-40 64-370-81
P3 100K Horiz. Trim, SB level 64-362-73 64-370-99
P4 10K Turn stereo, line volume 64-095-36 64-105-34
P5 10K Turn stereo, out volume 64-115-16 64-125-14

D1 AA119 70-018-94
D2-10 1N4148 70-005-57 Any diode

B1 Rect. bridge 6 pin DIL 70-084-02 70-084-51

IC1 LMC660, 14 pin DIL 73-660-24
IC2 TDA7050, 8 pin DIL 73-063-35
IC3 7806, TO220 73-091-56 73-090-65
J1,2 3,5mm stereo outlet 42-700-47
J4,5 Plint, Line connector 48-379-28 48-375-06
J6 9V Battery connector 42-042-02 42-041-78

RE1 Relay 5VDC DIL 37-043-50 37-072-13
RE2,3 Relay 5VDC 37-053-08

TR1,2 600 ohm Line transformer 56-562-51

Button, PTT 35-305-40 35-306-49
3,5mm stereo outlet, SB in 42-700-05 42-700-62
Thin stereo cable, SB-SimCom(c) 55-806-00 55-806-18
9V Battery or 5-12VAC/7-16VDC adaptor Chassi connector for AC adaptor, J6 42-050-92 42-050-50
Headset, with condenser microphone