Racing Sim Brake Pedal Load Cell Interface

A little while ago I undertook the process of scratch building my own PC racing sim.  It's all done now but one thing that i'd like to share with you all is how i accomplished a load sensitive brake pedal.

See, in a real car, the pedal does not really move all that much, even less in a race car.  The braking force is then proportional to the force applied to the pedal and not the MOVEMENT.  The problem lies in that most commercial pedal/wheel setups simply use a spring under the pedal and it detects movement of the pedal, but it just doesn't feel real.

Now, i don't claim to be the pioneer of this load cell idea but i would like to share the interface that i have made to enable one to be used.  There is at least one commercial LC interface available by itself or built into a USB joystick board but it seems they have effectively stopped selling them.  Hence, they are effectively unobtainable.

All you need to do is source yourself the INA122 chip from your fav electronics outlet - RS, Farnell, Mouser etc.  It should set you back less than $10 even in a single item purchase.

Print, transfer, etch and drill the board.  I used screw terminals on mine but they can be just soldered directly to the board.

The board layout is attached in Swift PCB format.  A free viewer/printer is available for download from them.

Solder the chip and 0.22uf cap in place and select your resistor for the gain.  Theoretically, a gain of about 500 is perfect so accoring to the datasheet it needs a 400R resistor.  This means we get very close to 5v output when the LC puts out 2 milivolts.

Providing your existing pot is running at 5v, you can simply substitute the three wires on the pot with the 3 wires on the LC interface (negative, +5v and signal) and you then have yourself the beginings of a load sensetive brake.