cheap student edition: adapt a CNY70 to the soundcard and use LabVIEW to analyse the sound input. (even cheaper: use the buildin mic of the notebook ..... if the machine emissions sound and you have a good guess of the speed to filter the main order)
However a good answer needs some more information about you requirements.... because there are MANY ways to solve that task.
Greetings from Germany
Henrik
LV since v3.1
“ground” is a convenient fantasy
'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'
