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--- rini:speed_log_notes [2009/04/17 04:36]
ben
+++ rini:speed_log_notes [2009/04/17 06:36]
ben
@@ Line 6: / Line 6: @@
   * Important is display type- black on white is best for sunlight conditions.  Backlight also required.  Maybe white on blue would work well in sunlight?
   * Important is character support- LARGE NUMBERS are necessary.
-== Basic Functional description ==
+=== Basic Functional description ===
   * X Buttons for functions Y
   * Calibration mode, 1 nautical mile, 1/2 nautical mile
-= Calibration method =
   * For now it seems that traveling 1 mile and counting the number of transducer clicks will provide an adequate average result
-  * Once the number of clicks for 1 mile is found, math is 1 n. mile per hour = 1 knot, choose a very small unit of time to count clicks for to allow fast updates of speed calculation (2s?)
+  * Once the number of clicks for 1 n. mile is found, math is Distance in n. mile divided by time in hours = Speed in  knots, choose a very small unit of time to count clicks for to allow fast updates of speed calculation (2s?)
-  * Click count... need to think through the math
+Best I can get this described in ASCII:
+<tab><blockquote>
+D = distance in nautical miles
+T = time in hours
+S = speed in knots
+D/T = S
+X = Number of clicks counted while traveling a calibration mile
+Y = Number of clicks counted in a single sample period
+Z = Sample period in Seconds
+D = Y/X * 1 n.m.
+T = Z/3600
+So:  (Y/X * 1 n.m.) / (Z/3600) = Speed in knots for the sample period Z
+E.G.  If we calibrate 1 n.m. at 2500 clicks (X=2500) and our sample/update period is 2 seconds (Z=2), and over that period we count 10 clicks (Y=10), then calculated speed would be (10/2500)/(2/3600) = S = 0.004 / 0.0006 = 6.67 knots.
+</blockquote>
 [[http://www.arduino.cc/playground/Code/LCD|Arduino LCD Code notes]]

..., etc.

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