Recent content by MurrayMD

It doesn't seem clear whether the time-varying amplitude varies over the period of the waveform or over the time the signal is produced. If it's over the period of the waveform, the signal can be expressed as a sum of sinusoidal signals, each having amplitudes that do not change with time. If...

It's amazing what you can find on the web. I was looking for more information on Fourier transforms and stumbled onto an excellent resource via a series of lectures posted on YouTube through a Stanford University outreach program. Excellent course, and the home page has all the course notes...

Wikipedia's article on magnetic declination has a link to the National Geophysical Data Center (NGDC) where there's an online geomagnetic declination calculator and other useful links: http://www.ngdc.noaa.gov/geomagmodels/Declination.jsp Geomagnetic north changes over both both time and...

A hot wire can work well for styrofoam but plastic sheet is more dense and will cut pretty slow. A straightedge and a sharp cutting blade will work quicker and cleaner, but you have to do it right the first time: make sure the blade is sharp and the straightedge won't slip. (A little...

If you want 3D orientation you need two vectors. Gravity gives you one. A magnetometer can give you the other.

Update: A company called "Building Performance Equipment, Inc." in New Jersey claims to get over 87% efficiency in their units. Their website is: http://www.lowkwh.com/exchangers.dws

Good question! I'm not exactly sure what the answer is, but my assumption has been that a single-stage passive exchanger could take the temperature differential to zero by heating the incoming air with the exhaust air until they're the same temperature. Perhaps subsequent stages could repeat...

Probably the main energy efficiency parameters for "most practical design" would be wall thickness and insulation type to prevent leakage via conduction and a good tight seal around the envelope to prevent leakage via air transfer. An air-to-air heat exchanger could heat (or cool) the incoming...

If I understand your problem correctly you want your phone to know its 3D orientation. You need at least two vectors to do that. The xyz accelerometer produces a gravity vector that goes straight down. An xyz magnetometer can provide a second vector that is horizontally towards magnetic north...