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The NaPiOn motion sensor is made by Panasonic product of Panasonic electronics. The automatic door opener uses the Area Reflective Type.The Area Reflective Type emits infrared rays from an LED.The sensor sens out a ray of light towards the object/human body then uses the reflected light to measure the distance and determine whether there is a person within the given distance of the sensor. When a sensor detects a person within its circumference of sight, it sets an output non-contact switch to ON. This type of sensor uses a series of complex embedded motion sensors with manually operated Program activators which are push buttons and switches,safety sensors that ensures that the doors do not get in contact with the user, Entrance control system,wireless program switch and a remote control.
Figure 1: Area Reflective Type Operation Principles
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The sensors have a built in sensor element,amplifiers and a comparator in a three-stage architectural structure . The output from the sensor element has an extremely weak signal in passive infrared scheme and the signal has to be amplified and then converted to an ON/OFF signal with a comparator circuit before output. When a body with temperature different to ambient of the surrounding, moves into the detection field of the sensor,the sensor responds with a small AC signal.The signal is a small voltage around a DC signal that varies,it is therefore compulsory to cancel the DC part of the signal and amplify the AC part. Because the signal is affected by interference from the environment ,a noise filter is necessary.
Figure 3: Schematic of the first architectural stage
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Figure 3 shows that noise is filtered by components R1 and C1,cut-off frequency of about 5 Hz. This application does not need to work at high frequency because usually we are detecting human motion. The second filter is used to cancel out the DC part of the signal, components R2 and C2 perform a high pass filter with a cut-off frequency of about 0.6 Hz. Because DC signal is not amplified,the input offset voltage of the Op-amp has no importance in this application. With a gain of just over 53, the amplification gives a signal that is higher than the noise level.
Figure 4: Schematic of Second architectural stage
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In the schematic the components R6,R7,R8 and R9 to Vcc/2 sets the Op-amp common mode which allows for greater amplification of AC signal in stage 2. A factor of 10 is used to avoid limitations with the gain bandwidth product (GBP).
Figure 5: Schematic of third architectural stage
This schematic allows the user to perform a window comparator,the signal is conditioned to a go to a micro-controller. The output of the Op-amp U3 and/or U4 is in low state when a heat source is detected. Components R6,R7,R8,R9 make up the divider bridge which is used to set the voltage reference of these devices. When the voltage reference of U3 and U4 are within the Vcc range,thus no constraint on the common input common mode voltage,the window comparator works.
When the signal (Vout2) is above this reference (2.77V if Vcc=3.3V),the output of U3 is in low state-close to ground.
component U4 is used to detect when the signal is below a certain reference.In our schematic the reference is 530mV thanks to the divider bridge and the Voltage calculation is thus :
Figure 6: NAND truth table
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