Note that this unit must be a compact separate board away from the microcontroller board to eliminate interference. It must have a solid ground connected only by one wire to the ground of the microcontroller board. 
GKOS Infrared Remote Control Mouse Unit
Calibrating (or biasing) the TrackPoint mouse amplifiers is done fully automatically by the microcontroller each time power is turned on. Resistor R2 value is 330k. With this value, the bias voltage can be adjusted by the Calibrate input within a range of +/-0,03 volts (e.g. 2,47...2,53 V). At Yin and Xin outputs, however, one calibration step is 0,2 V due to the large amplification required. This means that the voltages at LM358 input pins 2, 6 and 3/5 shall be equal within an accuracy of ca. +/-0,01...0,03 V when no calibrate signal is present (Calibrate not connected). This is most probably obtained by selecting the two 10k resistors, from the same production batch, as equal as possible by measuring them. Try to find two resistors showing e.g. 9,98k and 9,98k on the ohm meter.
The flat cable shown in the figure is a top view of a typical wiring coming out of a TrackPoint mouse unit stripped off an IBM laptop keyboard (by peeling off the plastic cover between the mouse and the metal plate). The cable is shown so that the TrackPoint mouse in on the right hand side (and numbers on the left hand side). Wires 2 and 5 must be connected together and also wires 4 and 1. They are not really joined inside the mouse even if it seems so in the figure.
Updated 4 September 2002