---snip--->> > Alternatively make a stroboscope disk (either copy the one off a TM100 > pulley, or work out howm many segments you need and write a trivial bit > of postscript to draw it), stick that on the spindle pulley or > direct-drive motor rotor and view it under amins-powered lamp. > Hi For 60 Hz it is easy. If one uses a light like a neon, it will flash 120 times. An LED is just one direction unless one uses a full wave bridge to get a forward pulse on each cycle. As a single phase it is only 60 Hz. One thing to remember is that the LED can't take too high of a back voltage. Most red ones are rated for about 10V someplace. If feeding it with an AC source greater than the LEDs rate back voltage, one should do something to protect it. A series rectifier diode will work and reduce the power in the dropping resistor. A shunt diode will also work but the resistor will conduct on both half cycles. Lets assume we have 120 flashes per second as from a neon since the same disk would work with the 60 flash LED. A disk spinning at 300 RPM does 5 rotations per second. if we divide 120 by 5, we get 24 flashes per rotation. We just need to create a disk with 24 dark and 24 white segments. For a 360, we get 6 rotations a second. That works out to 20 flashes per rotation. That is 20 black and 20 white spaces. This could be printed with a spread sheet and a pie chart print, as I stated before. For 50 Hz, the 300 RPM is easy but the 360 doesn't work out. One gets 16.66 flashes per rotation. The only way I can think to make this work is to make a spiral that would have 50 dark and light strips over 3 revolutions. Ones eye would tend to follow the spiral. I'm not sure how to do this with a spread sheet. Maybe it could be done with some postscript code but I'm not sure how. Dwight _________________________________________________________________ Your smile counts. The more smiles you share, the more we donate.? Join in. www.windowslive.com/smile?ocid=TXT_TAGLM_Wave2_oprsmilewlhmtagline