Left square wave generator is added to run simulation.
Circuit in simulator is revised VW Diesel Tachometer circuit. You supply your own tachometer.
Left LED and NPN transistor is EE-SB5 (non-amplified sensor) or Photointerrupter Reflective Phototransistor 4-pin on the Internet description.
Mechanical measure of low 300 RPM or less can be done with "egg beater" hand drill. Say one turn of hand crank is 4 or 5 turns of drill spindle. Mound small lead pencil with eraser in drill chuck and press against end of turning machinery spindle. Have stopwatch and count number of times hand crank turns in one minute.
Example: 60 hand crank turns in one minute and we have 5 drill shaft turns per hand crank. So, 60 times 5 would be 300 rpm.
My brother let me use his Laser Photo Tachometer CyberTech DT2234A and it was a surprise how far the belt pulley estimates was from the digital measure. Now, my arbor grinding wheel is 3698 RPM and my table saw 5592 RPM. An old shiny table saw blade had to be painted flat black and about a .5 inch reflective sticker tape on side of blade (it is thin and holds at high speed with no problem) to get right speed readout. If you have shiny metal allow time to mask, paint, and paint dry time as the measurement does not take long.
