Homemade tachometer help

[Smurf208]

Hi i'm building a very special jet turbine and its bearings are designed for max 120,000rpm. I've looked all over google for homemade tachometer circuits. I could use either 2 magnets for a magnetic rpm circuit or i could use a light probe? Does any1 know of a simple rpm tachometer i could build. Any circuit schematics or info would be great. I'm not the best with electronics but i've built a couple of small little circuit boards from parts from radio shack and simple designs off internet sites so i have some expirence with circuits. It would need atleast 4 digits in its screen and it could be digital, led, i just need anything that will do the job. I can play around with different designs and make them work as long as the electronics are taking care of. Anybody have anything?? Thanks

[NC Cams]

Check out the application note for LM2907 or LM2917.

The application sheet associated there with is very easy to follow if you can do a bit of math.

[Smurf208]

what is LM29017 or LM2917??? wheres the application sheet??

[Al_The_Man]

National Semi http://www.national.com/pf/LM/LM2907.html
Al.

[NC Cams]

You might want to check out a real neat internet search tool called GOOGLE.

The first DOZEN listings for "LM2907" or "LM2917" lists several links to application notes for the IC's.

Pick one.....

[Smurf208]

Ummmm anything a little more user friendly please??? This shouldn't be that hard i just need a simple home buildable circuit that will one way or the other let me know the speed of a rotating shaft!

[Smurf208]

Will do

[Al_The_Man]

The LM2907 doesn't get much easier than that, if you want simple, look at the off-the-shelf items like RedLion products from DigiKey.
Al.

[NC Cams]

The only thing easier than an LM2907/LM2917 is to BUY something already made.....

You might also find the following thread to be QUITE pertinent to this particular inquiry, especially with regard to doing internet research:

http://www.cnczone.com/forums/showth...9&page=1&pp=15
specifically post #15


Although the Red Lion stuff is off the shelf, it is not necessarily cheap. The 2907/2917 deal could give you a tach for $10 or less (plus the cost of a VOM) depending on what you already have.

[smarbaga]

hello:
i don't think any hall effect divice will detect a magnetic field that is changing at 120,000 times per second.
i think an opto would be your best bet.

[lerman]

http://www.oatleyelectronics.com/kits/k117.html

[pastera]

Originally Posted by smarbaga hello: i don't think any hall effect divice will detect a magnetic field that is changing at 120,000 times per second. i think an opto would be your best bet.

At 120,000 RPM it's only 2kHz - a hall sensor would be able to pick it up.

An optical solution would be easiest and most probably, more robust.
I have to go with NC Cams on this one - the LM2917 is definately a plug and play solution. Buy a cheap multimeter and build a circuit based on the LM2917 to output ~10mV per 1000RPM and you're done.

Aaron