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

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