Wiring

To begin with, let's take a look at the pin assignments for the standard PC joystick port;

The blue labels indicate the functions of the relevant pins in the joystick port e.g. J1 X means "Joystick 1 X-axis" and Btn 1 means "button/switch number 1". The pin numbers are shown in black.

*** When using the joystick port on a soundcard, avoid using pins 12 and 15. A soundcard uses these pins for MIDI TRANSMIT and MIDI RECEIVE respectively.

Potentiometers, or "pots", are used to measure the position of the joystick axes. Click here to see how they work.

Please see the electrical components list for a more detailed description of the parts refered to on this page.

Bearing in mind that our basic wheel will emulate the operation of a standard 2-axis, 2 button joystick we connect the potentiometers and switches as follows;

I have shown microswitches in these diagrams for the gear change switches (Sw1 and Sw2) because I have used these in my own wheel, but any momentary switch could be substituted. If microswitches are used, connections should be made to the C (common) and NO (normally open) terminals - these codes are typically marked on the switch housing.

Depending on the orientation of the steering pot in your own wheel, the connections made to the pot terminals may need to be altered - pin 1 (red wire on the diagram) will always go to the centre (wiper) terminal of the steering pot, but pin 3 (purple on the diagram) may need to be switched to the other outer terminal. See how potentiometers work to make this clearer.

The steering therefore equates to the left/right motion of a joystick, and the throttle/brake (combined by connecting their pots in series) equates to the forward/back motion of the joystick. This is a single-axis throttle/brake arrangement since both are operated by the same joystick axis, i.e. Joystick 1-Y. This means that if both throttle and brake pedals are pressed at the same time, they will effectively cancel each other out. This, in practice, is seldom a problem and in fact many games do not support anything other than single-axis throttle and brake.

Some of the more advanced simulators however, such as Grand Prix 2, Grand Prix Legends, TOCA 2 etc., allow the throttle and brake functions to be assigned to separate joystick axes. This allows the throttle and brake to be operated independantly of each other thus allowing the use of more advanced driving techniques such as trail-braking. The method of wiring a dual- or split-axis throttle/brake system is shown below.

When a dual axis setup is in use we are effectively using only one axis from the second joystick (Pin 11 - Joy2 X-axis). Windows and some games will not recognise that the "second" joystick is connected if there is not a voltage present on both Joystick 2 axes. To avoid this, we simply connect Pin 13 (Joy2 Y-axis) directly to Pin 1 or Pin 9.

Since many games do not support dual axis brake/throttle setups, it would be unwise to permanently wire up the wheel using this arrangement. Shown below therefore, is a switching circuit which will allow us to select between single- and dual-axis braking at the flick of a switch. This switch can either be positioned on the pedal unit or on the "dashboard".

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This circuit uses a DPDT (Double-Pole, Dual-Throw) switch to change between single- and dual-axis operation. When the switch is in the "UP" position (as shown on the diagram) then dual axes are selected. When in the "DOWN" position then a single axis is selected. The dotted lines around the top two pairs of terminals in the diagram represent the switch in the "UP" position and shows which terminals are connected together when in this state. Similarly, it is the bottom two pairs of terminals which are connected when the switch is in the "DOWN" position.

When assembly is complete and before the wheel is connected to the computer we need to calibrate and test the pots and circuitry.