The illumination level E is then measured (activity 8) by the
10 bit ADC embedded in the MCU which is connected to the
voltage divider formed by the LDR sensor and Rs (port P2.0 in
Fig. 2). If E is less than 50 lx and the change in B is less than
5 micro/T , we either have: (a) a nonferromagnetic object covering the
sensor; (b) a low-level local illumination (e.g., it is night time or
the sensor window is dirty); or (c) a vehicle parked nearby that
projects a shadow onto the sensor node