re long distance ir detection in article apr dres dnd ca sburton dres dnd ca stan burton writes i would like to be able to detect the angular position low accuracy of an ir emitting source at a distance of about meters more is better in daylight the ir source could be emitting a signature i m leaning toward khz square wave with duty cycle i am considering the use of a quadrant detector from centronic inc to give information to a pan tilt head to point the sensor and thus determine the angles for the source i am considering wazing the heck out of an ir led s possibly an optek op or motorola mled wazing would mean at least amp current pulses at this current the duty cycle of the led drops to and i would need to cycle five of them in turn to get the required has anyone done something like this stan burton dnd crad dres dtd mss agcg sburton dres dnd ca dre suffield box medicine hat ab canada t a k a method which will directly almost provide you with the information that you require is that which is commonly used for coordinate measurements of human body landmarks eg the selspot system by selspot ab sweden and the watsmart system these use lateral photoeffect detectors lindholm and oberg woltring and marsolais to determine the position of a spot of light projected using a camera lens over its surface in escence the detector is a large photodiode with four cathodes one on each of the four sides of the square detector crystal and a single anode the back of the crystal a spot of light will produce currents which are proportional to the position of the spot on the detector s face let s try some ascii graphics in d so the detector has two cathodes to detect linear position cathode xxxxx xxxxx light xxxxx divider output xxxxx xxxxx xxxxx xxxxx gnd xxxxx xxxxx anode xxxxx cathode if the dot of light from the led is the only source of light then the position of the projection is given by this circuit regardless of the level of illumina tion the divider is used to normalize relative to total received power when this circuit is used in the presence of other sources of light then the way of tuning to it is to sample for a few msec the background signal light the led for an equal time and sample that signal separately the difference between the two is the position of the led hamamatsu photonics sells linear and d lateral photoeffect detectors and they also sell the required signal processing electronics the ready made systems by selspot and others are not cheap lindholm l e and k e oberg an optoelectronic instrument for remote on line movement monitoring biotelemetry woltring h j and e b marsolais opto electronic selspot gait measure ments in two and three dimensional space a preliminary report bull pros thetics research most probably this technique can provide you with a much more accurate measurement than you need but i think that its simplicity beats scanning a quadrant detector with a pan tilt system until you reach zero difference david david prutchi hc dt washington university prutchi mesun wustl edu campus box dp cec wustl edu one brookings drive st louis mo
