Motion Detector Design Explanation - Renesas RL78/I1D User Manual

DETECT-IT RL78/I1D detector boards kit

Motion detector design explanation

The Motion detector demonstration can alarm when a human moves within 4 meters in front of the PIR (Pyroelectric
InfraRed) sensor within an angle of +/-45degrees vertically, and +/-70 degrees horizontally as measured from the
normal (apex) point perpendicular to the front of PIR sensor surface.
For this Motion sensor design, the 2 integrated operational amplifiers are used to monitor PIR sensor amplified voltage
and look for PIR levels exceeding the pre-determined thresholds. The operational amplifiers are used in high speed
mode in this Motion sensor demonstrator.
The PIR (Pyroelecctric InfraRed) sensor is the first element of the Analog Front End. The muRata part number IRA-
E700STO PIR sensor is used to detect IR energy changes that are detected when a warm object such as a human being
comes into the range of the sensor. PIR sensing of infrared energy is further enhanced by a white, translucent Fresnel
lens placed in front of the PIR transducer. The Fresnel lens has a hemispheric shape with a honey comb shaped cells in
the plastic mold. These Fresnel lens cell shapes then enhance the sensed IR energy peak-to-peak voltage changes as the
human being advances across the front of PIR sensor
The PIR sensor is connected to 2-stage processing analog front end:
 The first stage AC amplifier uses single channel Ch1 of RL78/I1D internal operational-amplifier in low power
mode at about 2.25µA typical current drain. This stage is AC coupled from the PIR sensor output to Ch1, so as
to eliminate any PIR DC bias variations. The stage 1 amplifier has a nominal gain of x101, and an upper roll-off
frequency ~15.9Hz.
 The second stage AC amplifier: uses single op-amp channel Ch0 has a nominal gain of x33.9 max (x6.7min) at
roll-off/cut-off frequency @32.9HZ max (6.5HZ min). The gain of this 2
potentiometer (labeled JP9). The input of the 2
output. However the output of 2
IVREF0. In all cases of the 1
each stage is less that the op-amp GBW = 40KHZ rating in low power mode. Since the op-amps have a low
current drain in low power mode, they can be left on constantly to monitor PIR sensor pulse energy. The output
of AMP0O is monitored by Comparator input IVCMP0, which is on the same MCU pin as AMP0O. The
explanation of Comparator function to trigger MCU wakeup is below.
So in this Motion sensor detector demonstration, only 2 operational amplifiers are used.
UM-YDETECT-IT-RL78 V1.30
Figure Motion sensor block diagram:
nd
stage is AC coupled (DC-blocked) from 1
nd
stage (AMP0O) is DC coupled to ADC input ANI4 and Comparator input
st nd
stage and 2 stage Amplifier settings, GBWP (gain x frequency product) used on
Kit User Manual
nd
stage is adjust by the 900KΩ
st
stage (AMP1O)
Page 8 of 59