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

I agree....
Here's my circuit using a simple IR tx/rx sensor
http://hans-w.com/RPM.gif
More details at http://hans-w.com/cnc.htm
Hans W

Tony Jeffree wrote:

> At 01:54 05/01/2003 -0700, you wrote:
> >Tony Jeffree wrote:
> > >
> > > If you use a pulse generator that gives 6 pulses per rev, then all you have
> > > to do is shift the decimal point one place to the right, rather than
> > > multiplying by 60. Use a 60PPR encoder, and it reads directly in RPM.
> > >
> >
> >Tony:
> >
> >That is a great observation! I just went to USDigitals encoder website
> >http://www.usdigital.com but didn't see any 60 PPR rotary encoders.
> >
> >However, they have some 120 PPR (they call it 120 cpr, which is 480 count
> >in quadrature) encoders.
> >
> >Prefaced by a divide-by-two chip, then, as you observed, the under-$20
> >frequency meter kit at http://www.qkits.com/serv/qkits/diy/pages/QK148.asp
> >would directly read out the 4 digit rpm.
> >
> >Its too bad that encoder doesn't seem to be available with an index option,
> >which would enable the lathe threading capabilities on software such as
> >TurboCNC http://www.dakeng.com/turbo.htm
> >
> >I do see a 360 PPR encoder with index available (1440 in quadrature),
> >and presumably using that with a divide-by-six chip would also enable
> >the direct readout of rpm.
> >
> >Doug Fortune
> >http://www.cncKITS.com
>
> Doug -
>
> Using a US Digital encoder for 6 PPR is massive overkill - you can buy
> simple reflective IR sensors, add a couple of resistors & you have your own
> encoder. Then just paint alternating black&white sectors on the rotating
> shaft, mount the reflective sensor close enough to register, and you're
> done. There's an example circuit on my website - see
>
> http://www.jeffree.co.uk/ModelEngineering.html
>
> and look for the article on "spindle and surface speed measurement".
>
> If you wanted an index pulse as well, it isn't going to bust the bank to
> add a second sensor looking at a single black/white sector.
>
> Loads of variations possible - other types of sensor can be used too, for
> example, the "slotted" type that need a perforated encoder disc. Cutting 6
> slots isn't hard!
>
> >
>
> Regards,
> Tony
>
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