DSO SHELL AUDIO SCOPE AS LAWNMOWER TACH

I had been curious to give this a try. If I have wrong calculations, let me know. Non working in sim to show hookup. Three loops of thin copper wire loosely wrapped around insulated sparkplug wire of old Weedeater push lawnmower. One end of wrapped wire grounded to engine metal. Very low readind around 15 miliamp on DSO SHELL SCOPE connected at top of wrapped copper wire and grounded at bottom of wrapped wire.so I could have went with more loops of copper wire. Duty cycle reading around 33 %. My calculation: Scope reading of 3.754 Hz. X 60 seconds =225.24 fires per minute. 4 stroke engine so we take 225.24 X 4 = 900.96 RPM. Red line speed for lawnmower is 3600 rpm. Today, The engine shaft spins at 2900 rpm on a walk behind mower. A blades on riding mower typically spin between 2700 and 3200 rpm or 200 mph plus at the tip of the blade. The government regulates the tip speed of the blade, not the rpm of the engine.

published 2 years ago