Silicon Laboratories Si1120-EK User Manual page 7

The data for these channels represents a measurement of the duration of the Si1120's PRX low time, as seen
by the C8051F930 MCU. The Y axis indicates the number of 6.125 MHz clock cycles that occurred while PRX
was low. The maximum output limit of the Si1120 is 2 ms, which would correspond to 12250 counts of a
6.125 MHz clock.
2. Linearized distance measurements for each IR channel. The raw proximity values output from the Si1120 will be
exponentially larger the closer an object is to the sensor. The channels labeled "Radius 1", "Radius 2" and
"Radius 3" are linearizations of the raw data output from the sensor when illuminating the three different
selected emitters. To use the example effectively, the shorting blocks on header J1 should be set according to
the diagram in Figure 1. This will select D1, D4, and D7 as the three reference emitters.
3. Calculated coordinate measurements. The linearized IR proximity measurements are used to calculate X (left-
to-right), y (up-to-down) and a Z (far-to-near) measurements.
Due to the nature of infrared proximity measurements, the object's size and reflectivity will have an impact on the
values measured.
Rev. 0.3
Si1120-EK
7