Motion Detector


Posted on Feb 5, 2014

The motion detector circuit consists of two components, the emitter and the sensor/detector. The emitter is simply made up of an infrared emitting diode reverse biased to a 5-volt source. The sensor uses the MRD821 to detect the IR beam from the emitter. It outputs a high of around 9 to 10-volts when the IR beam shines directly to it. If the beam


Motion Detector
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is cut, it outputs a low of around 0. 4 to 2-volts. This signal is fed into pins 2 and 6 of a 555 timer, which in turn outputs the amplified signal at pin 3. The output is a TTL low when the IR beam is continuous and TTL high when the beam is cut. (Actually, outputs of about 6 to 7-volts are sometimes measured. A de-amplifier could be added at the end of the circuit to make sure the output does not exceed TTL levels. ) The schematic diagram of both emitter and detector are shown in figure 1. There are three pairs of such sensors interfaced to the computer through the printer port. In order for motion to be sensed, a moving object must simultaneously trigger at least two of the detectors signifying that it has moved from one point to another. If the sensors have established motion, the controlling program proceeds to the appropriate routine. // IR Array Program Driver Program // Decoding is done via software int irmotion(){ int count=0, trigger=0, sensor=0; //initialize trigger & count flag int motion[3]={0x00, 0x00, 0x00}; //initialize array for sensor status outportb(0x37a, 0x08); //get mux`s attention outportb(0x37a, 0x08); //get mux`s attention do{ sensor=0; sensor=inportb(0x379); //get value at this port sensor=sensor & 0x70; //mask it motion[0]=sensor & 0x10; //assign status of each sensor motion[1]=sensor & 0x20; //as an element in motion array motion[2]=sensor & 0x40; if(motion[0]=0x10){ //at least 2 sensors must be...




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