Re: [CAD_CAM_EDM_DRO] Cheap tach - was r.p.m. kit??? / 4 digit under $20

I've been thinking on and off about adding a digital readout to my bandsaw to
read blade speed in fpm (it's a varispeed DoAll). This would be the easiest:
just run a motor with a small rubber wheel against one of the band wheels, use
a pot for calibration and run it to one of those cheap 2V LCD or LED voltmeters.
Worst case would be to add an op-amp amplifier.

Very cool (and much easier than the PIC solution I was leaning toward). Sometimes
low-tech is the answer.

Paul

> > Hi, I just tried one of the suggestions on another group regarding
> > this subject. I was intrigued by the simplicity of the idea and the
> > fellow mentioned that this is an old trick thats been around a while.
> > You just need any small DC motor, a potentiometer, and a volt meter.
> > The first potentiometer that I found in the junk drawer was a 50K
> > although other values will work. I hooked it up as in this picture.
> >
> > http://www.members.shaw.ca/axxus4/cheaptach.jpg
> >
> > The motor is connected across the pot and the meter is connected from
> > the center of the pot to one side. To calibrate, spin the motor in the
> > chuck, and adjust the pot to read your known rpm (in mV or whatever).
> > I was spinning it at 1460rpm in my mill drill. I adjusted the pot to
> > read about 1.460V on the 20V scale. I walked over to the drill press,
> > and spun the motor. I read 0.354V. I was amazed to see that the drill
> > press was set to 360rpm. Very neat trick. I will use this method to
> > measure servo and stepper rpm.
> >

--
Paul Amaranth, GCIH | Rochester MI, USA
Aurora Group, Inc. | Security, Systems & Software
paul@... | Unix & Windows