Electronic Knot speed meter for boating
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Initially this project came about as the device stopped working. Assuming the circuitry as its about 30 years old, i started working towards replacing it with an arduino to process the sensor signal into output for the speed needle.
But during testing it started working, so im putting this on hold.
A stepper motor drives this gear, mine had pretty much completely disintegrated, replacements arent cheap but are available:
http://www.odometergears.com/products/VDO+Sumlog/All/31
AU reseller: http://www.repairsonly.com.au/VDO SUMLOG.HTML
Hooked the spinning water speed sensor up to 12v and oscilloscope with a 5k resistor between +ve and signal wire, captured this signal while wheel spinning.
Sensor is a hall effect sensor, my spinner had 3 magnets evenly spaced between the 6 spinner blades, there are several different sized spinners depending on what speed range you want to measure best.
http://www.furneauxriddall.com/acatalog/Sumlog_SL___HS_Spares.html
Change in speed effects frequency, period stays pretty much the same.
Sensor wiring is, green signal, white +12v, brown ground.
hayden
Jakob Flierl
Emach00
Dialog Semiconductor