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

The non-contact photo sensor is easily the simplest form for home
brew, but man it would be cooool to have a tach from a old Vette or
or Jag.

now that would wow the spectators!

Personally, I looked at the simplicity of just monitoring the pulses,
looked at mouse innards for sensors, and just stopped when you can
buy a kit for $20.00.

For just a few more parts, it would be easy to add a single point to
allow rotation count/posistion for threading.

Dave



--- In CAD_CAM_EDM_DRO@yahoogroups.com, Hans Wedemeyer <xyz@h...>
wrote:

> Yes it's a simple idea.... but nothing like looking at some digits

and not having

> to bother with coupling to a moving parts and the danger associated

with it.

> Fingers and eyes can be difficult to replace.... ! Now if you make

it a permanent fixture

> sure it's great...
> I'd say the idea has been around about 100+ years ! :-)
> The eddy current driven version has been around almost as long, in

most cars it known as the speedometer !

> If you goto a car junk yard you may even be able to find one of the

older eddy current version speedo's and

> adapt it directly to the mill.... just a thought... give me LED's

and LCD's any day... ! :-)

>
> Best Regards
> Hans W
>
>
>
> "deanc500 " wrote:
>
> > 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.
> >
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