http://humancond.org/ 2012-05-19T21:55:19-04:00 http://humancond.org/ http://humancond.org/lib/tpl/arctic/images/favicon.ico text/html 2010-05-31T12:18:38-04:00 http://humancond.org/wiki/user/ram/electro/capsense/0main?rev=1275322718&do=diff Spread Spectrum Capacitive Sensor [Measurement Unit] I have developed an extremely sensitive capacitive sensor which can detect a person over 1 meter away. It operates using a pseudo-random excitation signal, which is novel for a capacitive sensor. This allows high sensitivity to be achieved in the (inevitable) presence of interfering signals. The sensor also has seven measurement channels, which allow the location and motion of objects to be detected. This sensor was developed primarily to b… text/html 2010-06-09T23:43:39-04:00 http://humancond.org/wiki/user/ram/electro/capsense/description?rev=1276141419&do=diff System Description Principle of Operation: The basic principle of operation is to measure the current that flows in the antenna when it is excited by a constant voltage. In order to achieve simple high-performance current measurement, the excitation signal is used as the ground of the measurement circuitry. After conditioning and digitization, the signal is re-referenced to earth ground using opto-isolation. text/html 2010-05-31T13:06:06-04:00 http://humancond.org/wiki/user/ram/electro/capsense/intro?rev=1275325566&do=diff What is a Capacitive Sensor? A capacitive sensor is a proximity sensor that detects nearby objects by their effect on the electrical field created by the sensor. Simple capacitive sensors have been commercially available for many years, and have found a niche in nonmetallic object detection, but are limited to short ranges, typically less than 1 cm. text/html 2010-05-31T12:57:40-04:00 http://humancond.org/wiki/user/ram/electro/capsense/performance?rev=1275325060&do=diff Performance Evaluation For the graphs shown here, the background subtraction time window is equal to the graph interval, so the lowest point on each sensor response is always zero. The Y axis (labeled capacitance) is the increase in capacitance above this minimum value. This is a change (motion) detection mode, where only increases in the recent past have any effect on the output.