Z8FS021 Datasheet, PDF (27/68 Pages) Zilog, Inc. – Select from an assortment of lenses and pyroelectric sensors to best fit your application

ZMOTION^® Intrusion Detection
Product Specification
19
V_REF signal is no longer connected to ANA3 negative (–) ADC input. The fist PIR sensor
is connected to the positive (+) ADC input (ANA2) as it is in Single Pyro Mode. The
V_REF signal is still used internally for the ADC, but the external pin is unused in Dual
Pyro Mode.
White Light Detection and Status LED
When enabled via the White Light Threshold field in the PIR Status/Control Register 2,
the PIR Engine automatically performs ADC conversions on the ANA1 input. The signal
on this input should be proportional to the amount of white light to which the PIR sensor is
being subjected. Typically, this pin would be connected to a high-efficiency (status) LED
which generates a small voltage in the presence of white light. The PIR Engine configures
the pin to a (single-ended) analog input, perform the necessary ADC conversion and
reconfigure it to a digital output. See the following White Light Detection section for more
information about the operation of this mode.
White Light Detection
Due to the nature of the pyroelectric sensor, sudden large changes in white light will cause
a DC shift in the signal output, which could potentially generate a false motion event.
Sources such as car headlights have been known to cause this issue. The PIR Engine can
monitor this occurrence and be configured to ignore the event.
When light hits the pyroelectric sensor, its energy is converted into a signal output. If the
pattern and intensity of the light is optimal, then the signal can appear exactly like a
motion event. However, the PIR Engine can determine when the sensor is being exposed
to light and use this information to filter out an invalid motion event.
When enabled via the White Light Threshold (WLT) bits in the ePIR_SC2 Register (see
Table 10 on page 31), the PIR Engine automatically performs ADC conversions on
ANA1, which should be connected to a high-efficiency LED (typically a status LED).
When light shines on an LED, it generates a small voltage which the PIR Engine can mea-
sure. The PIR Engine reconfigures the pin to an analog input and performs the necessary
ADC conversion. The system should be configured such that if light is shining on the
LED, it is also shining on the PIR sensor. As a result, it is advisable to avoid placing the
LED behind a lens with white light filtering.
When the Engine detects a sudden change in voltage on ANA1 greater than the value set
in the White Light Threshold field of ePIR_SC2, the motion detection algorithms auto-
matically compensate for the associated signal level shift from the pyroelectric sensor
(caused by the light simultaneously shining on the LED and the pyroelectric sensor). This
compensation allows the PIR Engine to suppress false motion events caused by White
Light while still detecting real motion events. However, sensitivity is reduced during this
period. The White Light Detected bit of the ePIR_ASC0 Register is set to indicate the
PS028806-0315
White Light Detection