Foreword:
    This is a report which shows how to cut the cost of a homebuilt flight simulator by many hundreds of dollars through the use of keyboard interfacing. For anyone who hasn't had the pleasure of gazing upon Kev Saker's fantastic homebuilt flight simulator, you should definitely click here and check it out.

Introduction
    By inspiration from the flightsim genius Kev Saker, I decided to try a brief suggestion given by him in one of his articles, on FlightSim.Com, as it relates to hard-wiring the entire simulator to a keyboard card and it worked. By doing this, you will need NO solenoids or EPIC cards whatsoever. The cost of the entire electrical interface (not counting wiring or switches) is around $15 versus the EPIC card method which could cost hundreds or even more than $1000. I will attempt to describe the concept behind this new electrical interface so that you can use this technique with any aircraft you'd like.
    Since the last report, digital images have replaced the more primitive hand drawings in hopes of clarifying information.

The Interface
    If you plan to use indicator lights, please do not put them on the same switches and lines as the keyboard card or you will most likely blow the keyboard card out. Figure E1-4 (near the bottom of the page), shows a proper technique for connecting indicator lights without disturbing the keyboard card. E1-4 is a more complex component, so refer to figure 1-2 to see the simplified version. Remember that the keyboard supplies its own power supply so you will not need to worry about any manual power supplies unless you intend to use indicator lights.

Materials
    To construct the electronic interface for your simulator, you will need a keyboard, switches and lots of wire. The type of each of these parts that you will need is as follows:

Keyboard: I would advise that you use the AT style 5-pin keyboard rather than PS/2. If you have a PS/2 style port on your computer, you can buy an adapter from most computer accessory retailers for less than $5. The reason I would advise that you use this style of keyboard is that you can desolder the two signal ports on the card and replace them with your own wire (This is a hundred times easier than it sounds). Everything should work exactly the same using a PS/2 keyboard though, so if you would rather use one, go for it.

Switches: Only momentary buttons should be used in conjunction with the keyboard card, or else you will get a key repeat whenever you activate a button. A recent exception has been discovered and is discussed near the end of this page.

Wires: Try not to use wire too thin or you may chance the wire melting or overheating. 20 - 22 Gauge is optimum. The wire you buy should be solid (not stranded).

8-Position Barrier Strips: These strips allow you to instantly connect a wire to an extension wire on the keyboard card using only a small screw driver. They also prevent the exposed ends of each wire from touching thereby preventing signal crossovers.

Constructing The Interface
    You will now need to strip the keyboard down until you are left with three transparent sheets, an electronic keyboard card, and a long connector cord. Do not remove the plastic sheets yet because they play an EXTREMELY important part in this interface. The part of the keyboard that you will need to be concerned with are the two slots that the transparent sheets are connected to. By connecting a wire from the "short" slot to the "long" slot, you can create any keyboard output that you'd like. Each keyboard has different signal requirements (slot combinations) and that is why you'll need the transparent sheets to determine which pins on each slot control each letter. You may also want to keep the keypad so that you can determine which node on the sheets corresponds to the letter you want.

    The sheets work like a schematic and work as follows: If you want to create the letter "g", you would directly line up the transparent sheets and place them in an upright position. Now locate the node which corresponds to the letter "g" as in figure E1-1 (place the sheets on top of the keypad to help locate the node if needed). Now, on the top sheet, locate the node that you just marked/remembered for the letter "g" and follow the line that it is on until you reach the signal port (long slot or short slot) on the keyboard card as in figure E1-1. Now, note which pin the line ended at, and repeat this process for the bottom sheet. These two values represent the signal required to create the letter "g". The shortcut method to this is to simply cut a short wire and connect it between each port and record on a sheet of paper what letter was produced. In other words, bridge the wire between port 1s, and 1L, and record what letter is produced, then bridge the wire between ports 1s and 2L and record the letter produced... etc. You should then have a chart of every key on you keyboard and what letter it produces. Of course You will need to connect your keyboard card to your compuer to do this.

    1s, 2L

    1 - A port number
    s - symbolizes that the coefficient represents a port on the short slot
    2 - A port number
    L - symbolizes that the coefficient represents a port on the long slot...

    So the values on the diagram below could be summarized as 4s, 10L

    Now to send the signal for this key to the computer, all you need to do is take a wire and place one end in the pin you marked on the short slot, and place the other end in the pin you marked for the second slot as in figure E1-2 (once you remove the transparent sheets). As you can see, Figures E1-1 and E1-2 are exactly the same except one uses the transparent sheets, and the other uses wire and a micro (lever) switch, although any momentary push button will work. That's it. You have just created the letter "g". It is a hundred times easier every time you do it and you can now repeat this process for each switch and button you plan to use. Now, you may safely remove the transparent sheets. The middle sheet, that has nothing on it, is useless and can be discarded at your own leisure unless you plan to reassemble the keyboard. There are a few major points that I must make in regards to the interface before you begin adding a lot of buttons.
 

    Because many letters will use any given node, and the nodes are very small, it will be necessary to connect extensions as shown in figure E1-3c. These are nothing but strips of wire with one end connected to a pin and the other end left free or connected to a terminal/barrier. This will allow you to add as many wires to each slot as necessary. Whenever you want to connect a switch to a particular pin on the keyboard card, you will instead connect it to the corresponding extension wire or terminal. If you use a terminal strip, you will only need to screw the wire into the proper terminal, but without terminals you will have to fire up your soldering iron every time you want to attach wires. John Hastie from Australia provided a very helpful technique in which you remove the signal ports (the long and short slots that the transparent sheets were connected to) in order to allow the easy connection of your extension wires. To do this, flip the keyboard card over and locate the soldered pins directly beneath the long and short slots. Desolder all pins directly beneath the two slots, and remove the two connection slots. Then proceed to solder in your own extension wires as shown in figure E1-3c.

    Figure E1-4 shows how the landing gear panel would generally look using indicator lights, and using Kev Saker's gear switch setup. By connecting the up and down micros to the proper extension wires on the keyboard card, you can easily create a working landing gear lever. You can add indicator lights to the panel as well by connecting the gear lever to a SPST (Single-Pole Single Throw) switch and connecting each of the indicator lights to extension wires from that switch. Just remember to keep the indicator lights' power supply off the same lines as the keyboard card.

Creating Multiple Signals With One Switch
   A good friend of mine and fellow flightsim builder Peter Cos recently obtained a great schematic for creating multiple button presses with one switch. We call the schematic the Popescu circuit in honor of his father in law who created it for us. It utilizes a 4066 Quad Bilateral Switch and will allow the proper creation of items such the autopilot along with any function which requires button presses such as "SHIFT + Z." Testing of this circuit needs to be performed before the official release of the schematic, but at that time it will be posted on my main web site with Peter's permission.

Using Toggle Switches
    A recent accident has yielded a new possibility with the use of toggle switches in this interface. If you connect a toggle switch to the keyboard card and activate it, you will get a key repeat. But if you press another button while the toggle switch is activated, the button will totally cancel the signal from the toggle switch. The keyboard card then acts as if the toggle switch had never been activated. This cancelling signal could be a button combination on the keyboard which Microsoft Flight Simulator does not need such as CTRL + 1. The delay in the signal should be approximately 1/8 of a seecond and could be produced by a 555 timer. I haven't done extensive testing of this theory, but I have done enough to know that it has possibilities and is definitely worth checking out for those daring builders who are building analogue cockpits. I will post results after testing has been completed.

Preventing the need for Multiple Keypresses
    There is a VERY simple method to circumnavigate having to create multiple signals with any given button. In Microsoft Flight Sim, there are at least 30 single keys (i.e. ";", "x", and "[") which have almost no use whatsoever in the simulator. There are also 33 very important functions requiring multiple keypresses (i.e. "SHIFT + Z", "SHIFT + H", and "SHIFT + /"). You can swap the assigned keys for the unnecessary functions, with those of the important functions thereby almost totally eliminating the need for multiple keypresses.

    Below is a list of functions in Microsoft Flight Simulator that can be reassigned since they have little or no use in a homebuilt sim:

** FS98 Only

Building Your Simulator - (The 777 Project)

   Keyboard interfacing is just one part of what has recently become a very detailed project called 'The 777 Project'. The main web site contains step-by-step instructions on how to actually build the physical simulator, and any updates to the keyboard interface will be listed there as soon as they take place. A full bill of materials, dimensions listing, and detailed documentation can be found at http://www.buildingasim.cjb.net.

    Any questions, suggestions, or comments about the electronic interface or The 777 Project can be sent to Robert Prather at AirPanther@buildingasim.cjb.net and will be answered A.S.A.P.