Re: [CAD_CAM_EDM_DRO] Digest Number 1685

> At the recent P.R.I.M.E. show the Sherline booth had on display a conversion
> to the pulleys that gave the machine up to 10,000 rpm capability. As one of
> my interests for this machine is engraving I thought it a worthy
> conversion... so I made my own. And it works! My question is; do any of you
> worthies know of a source for a tachometer kit, schematic, or plans for an
> optical pickup tachometer reading to the 10K to 20K rpm level in probably 3
> digits ( x100 )?

You might get a cheap optical model airplane tach - designed to read
say 1800 RPM to 30krpm on a 2 or 3 bladed propeller. Try tower
hobbies.

A cheap idea would be to make a disk/optical interrupter with 1-4
holes and connect it to a speaker. If one has a musical ear, and
something like a piano around for reference, it might be possible to
figure it out by ear.

It should also be possible to count this several hundred hz signal
with a computer... especially if one designed a wheel or used a toggle
flipflop to give square wave output.

Or the ARRL handbook has a schematic for a frequency counter chip that
directly drives a multidigit 7-segment display. Should be possible to
get that working with an appropriate reference crystal frequency.

Personally, I'd estimate it mathematically from known rpms and
ratios, use an oscilloscope with a few pulses per second wheel, or
buy the model airplane tach, probably in that order.

Chris