[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 :cheers:

[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]

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

[Smurf208]

OPTICAL TACHOMETER KIT: This kit measures RPM of propeller shafts etc. without physical contact. Similar to the kit published in Silicon Chip magazine May 1988, but includes a crystal controlled calibrator. Use a Digital Multimeter on 200mV or a 3.5 digit panel meter as the display. Kit includes PCB and all on-board components.

That optical sensor kit looks like what i've been looking for, includes all the major parts, all i have to do is provide a multimeter? Have you any personal expirence with this kit? I think this is what i'll end up with. Simplest solution to my problem of measuring rpm. If i can't find anything homemade i'm gunna probally order this.

[vulcom1]

If anybody is wondering if a hall sensor will pick up the magnet they have been used in turbines for quite awhile. I think the 5 Bears site has a description on machining the nut for the nose. I am glad you gave a chip number for making one as the schematic from the GTBA is a lot of work for somebody that is an amature. I was starting to resign myself to buying one but as a hobbiest I like to build my own.
Thanks, John

[NC Cams]

Smurf: what are you going to do if you buy the "magic tach kit" referenced in post #13 only top find the it reads 20,000 rpm MAX full scale???? Punt???

Why 20k? Most IC engines used to power prop based planes won't turn more than 20K and most VOM's read 1999 as the max scaling factor.

Unless you look up the May 1988 issue of Silicon Chip magazine (or they provide a copy with the the kit) and see if the circuit is fast enough and can be reformatted to run at the speed/frequency you want to run at (120,000 rpm or 2000hz), you STILL won't have a "simple, build it to print" tachometer that you seem to be asking for.

Whether you use the "magic kit" or a 2907 or something else, you still may have to redo the scaling factor to get the RPM range to read what you're spinning at. Keep in mind that scaling factor of 1999 for VOM's that you have to deal with no matter what system you use.

However, the use of the sensor out of the magic kit or (if you'r lucky and they show/tell you how to rescale for 120,000 revs an you use the whole thing), you're STILL probably going to have to do some math to figure out timing values to get the thing to run with whatever meter function you find/ cook up for your situation.

Aaron: I have this feeling that untill or unless someone works out the values for the timing components on the 2907 (or for that matter ANY tachometer DIY kit found for this project), the "simple tachometer circuit" being sought by the member can't/won't be "simple" enough.

Perhaps you are in a mood to do the math - I"m not. If your or someone does do the math for the inquiring member, I contend that typ of thing occurs when too much of someones else's "yourself" is injected into an inquiring member's DIY project.

Vulbom1: if you figure out how to use the 2907, perhaps you'll be in a mood to show Smurf. Looks like he's not interested in using perhaps the most easily adapted, least expensive IC for creating an analog tach the I've ever seen/used.

[pastera]

NC
I would layout a circuit, hell cut on my PCB router for postage IF the person was willing to do some work.

Smurf - you can always buy a frequency meter and multiply by 60. Also, take a look at National Semiconductor application note AN-162. If you decide to do any of the research and have any further questions, I can help.

Aaron

[Smurf208]

Thanks Aaron. I don't know about all this freqency stuff any more it got complicated and ya, i already spent alot of time looking around for something to work and freq stuff is just too much for me, its not a simply design that will work very simple and theres no point spending huge amounts of time researching and trying to make a design that isn't promising. I need something that will just work in the end and the optical design looks alot simplier to learn,build,and do the job. Freqqency stuff just gets all complicated with numbers conversions etc. Ya freq to voltage rpm stuff may be easy for you guys to build, tweak, tune, but to me its confusing and not promising. Unless i come across a user friendly freq.to.volt site i think its going to be optical, i just got to find the right optical system yet. Grrr this rpm is giving me more then i bargained for, all i wanted was a simple little circuit i could just build that would accuartly measure up to 120,000, but nooo it heres some websites, have fun researching it for the next couple weeks to get a simple design that will simply work if you didn't mess up any calculations along the way.

[NC Cams]

Smurf:

You are missing the point entirely. The 2907 is not simply "promising", it works when you assemble the circuit liste in the app note with the right resistors and capacitors to scale the output for the 120K RPM that you're trying to sense.

Questinon: Once you optically sense the rotation (usually a hash mark or something like that), you have to turn that into an RPM. HOW DO YOU PLAN TO DO THAT?????? It doesn't just "happen" - a circuit has to be engineered to do that conversion.

THere are essentially 2 ways to affect such a circuit:

You can find a way to figure out how much time ellapses between when each equally spaced optically sense pulse comes by. Then do the math REAL FAST and if you do it properly and correctly, you'll then know the RPM. This is what a microprocessor based tach will do.

Oops, but to do that, you'd have to do "....Freqqency stuff (that) just gets all complicated with numbers conversions etc..." to get RPM. So, you pretty much have ruled out the building of a DIY microprocessor based tach.

OR

You can consider the "pulse" that's coming by repeatedly as a frequency. This can then be readily turned into a voltage by the 2907. This exact same conversion is done by any number of circuits that you were referred to in earlier postings.

Sadly and unfortunately, the undavoidable fact or ANY electronic project that takes revolutions and tries to turn it into a scalar factor measured over time, you once again encounter "...Freqqency stuff (that) just gets all complicated with numbers conversions etc...".

Whether you like it or not, whether you recognize it or not and/or whether you want to do the math to create a DIY tach, THAT IS HOW A TACHOMETER WORKS and the "..."...Freqqency stuff (that) just gets all complicated with numbers conversions etc..." is an unavoidable issue that you'd better accept as having to deal with.

If you want to do ANY sort of DIY tach circuit, you WILL HAVE TO DEAL WITH ""...Freqqency stuff (that) just gets all complicated with numbers conversions etc...". Get over it.

If you don't want to deal with ""...Freqqency stuff (that) just gets all complicated with numbers conversions etc...", buy something that is premade.

The 2907 circuits thay you've been referred to time and time again are the simplest, is easiest to use, most "convertrible" tach IC that you can buy - outside of a premade one.

There probably is not going to be a magicallly preconcieved DIY 120,000 rpm tach (outside of something you buy that is already configured as a jet tach) that you can "bolt together".

I can't help but think/conclude/feel at this point that unless you GOYA as do some calculations and make an effort at building a DIY tach using the suggestions provided, you can forget a DIY tach.

Oh, and by the way, simple and/or complex circuit designs will "simply work" if you do NOT mess up the calculations. Pencil erasers and CE or C keys on calculators are put there in case you just might input a wrong value if/when you eventually DO perform a circuit value calculation. You might want to give it a try - it does often lead to some interesting learning experiences....

By the way, if you do fudge up the 2907 calcs, the thing doesn't explode or do anything dangerous - it simply give off a bogus RPM reading. A freq meter or an oscilloscope can be used to cross check RPM vs tach output corelation. Oops, that however will require, "...Freqqency stuff (that) just gets all complicated with numbers conversions etc...".

Ain't it sort of amazing how those PITA issues keep rearing their ugly heads with respect to this particular DIY project?????

[pastera]

We really aren't trying to torment you, it's just that you were given the information but refused to respond with even a rudimentary question.

Did you actually read the datasheet and application note?
If you have no electronics knowledge, that's fine just say so.

BTW: I am an electrical engineer and NC is a mechanical - either one of us can answer any questions you have to help you around the stumbling blocks.

Do the calcs and post your results, I can verify accuracy so you don't chase your tail.

Calibration is as close as your nearest light bulb (120Hz - 7200rpm) or transformer (60 Hz - 3600 rpm) depending on the sensor type.

Aaron