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Stamp tachometer problems

--There's a site up with an excellent description of how to build a tach with a Basic Stamp, at:

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I built this circuit the other day, then had an expert pal make sure I hadn't done anything wrong (left out one wire!). Once all was set to rights I tried the three programs to see what would happen. First one: got some readings on the debug screen when waving a magnet back and forth near the sensor: a good sign, yes? So then I loaded the second program and got the proper responses from the display, so all was well there. After loading the third program things started to get weird; i.e. we were unable to get consistent readings. What I did is tape a neodymium magnet to the edge of a little 2" sanding disk, chuck it in a small drill and power it up near the sensor. It seemed to do *something* but not what I expected; i.e. sometimes I'd get a reading after I removed the rotating magnet, but not while it was spinning. I thought maybe the neodymium magnet was too strong and switched to a weaker one but results were just as weird. I'm wondering: might there be a problem with the "flywheel" being too small in diameter? Don't think this could be the problem but one never knows. There were also times when the numbers displayed were almost random; i.e. readings being much higher than the rate at which we waved magnets near sensor. It was all a bit baffling. We're sort of in the dark here, so any clues folks can pass along would be greatly appreciated. Thanks,

--
        "Steamboat Ed" Haas         :  Currently broke and  
        Hacking the Trailing Edge!  :  looking for a job...
                          www.nmpproducts.com
                   ---Decks a-wash in a sea of words---
Reply to
steamer
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sure

Did you try it slow? Did you try the 1st and 2nd program with the wheel on the drill? If you have an oscilloscope, you should look at the output from the pickup -- that'll tell you if it's clean.

You're getting a program for free, and you're hoping to gain more value from it than you paid, it could just not work right.

--
www.wescottdesign.com
Reply to
Tim Wescott

Yes, a good sign. Did you get the proper number displayed that matched the number of times you waved the magnet back and forth?

8888 and then 2845, as per the site you mentioned?

The motor may be affecting the sensor, or broadcasting electrical noise into the circuit. Try a different setup that does not use that drill - or any electrical motor, for that matter. Also, be sure to run your circuit from a good 9V battery - NOT a power supply.

No. Flywheel diameter has nothing to do with it. Spacing between the magnet and the hall sensor is a factor, as is RPM at which the flywheel is moving.

That makes it sound like the results from program one were not correct. You need to be able to count the number of waves correctly: "At this time you test the program moving the magnet close to the Hall sensor. In the debug screen will see how many times you moved the magnet back and fort per sec, that number than is multiplied by 60 and gives you pluses per minute."

If you can't get the correct results here, then you won't get the correct results with program 3. I'd suspect a wiring error.

Ed

Reply to
ehsjr

--Yes; max rpm maybe 400.

--Yes

--Good idea; will try that next.

--Heh, yeah; still I live in hope that some day I'll be able to get reliable numbers for my steam engines..

--
        "Steamboat Ed" Haas         :  Currently broke and  
        Hacking the Trailing Edge!  :  looking for a job...
                          www.nmpproducts.com
                   ---Decks a-wash in a sea of words---
Reply to
steamer

--Not really; chalked it up to inconsistent speed of magnet, but...

--Yes, just so.

--Hmmm; well I'll point out that the drill was on a flex shaft so motor was well removed. --Re: battery vs wall wart: will try that too; thanks!

--
        "Steamboat Ed" Haas         :  Currently broke and  
        Hacking the Trailing Edge!  :  looking for a job...
                          www.nmpproducts.com
                   ---Decks a-wash in a sea of words---
Reply to
steamer

If you want to test your sensor setup on an independent tachometer, you can download my Daqarta app that uses your sound card for input. One advantage of this is that you can see the input waveform and play with the triggering, which may give clues to your Basic Stamp problem.

If the discussion below isn't adequate, note that you can right-click any control to get Help about it. (Or ask me!)

Click on the thin button below 'Input' on the toolbar to open the Input control dialog, and make sure Line In is set. You can connect your sensor to a standard sound card audio cable cable using mini-gator clips. The tip is Left, which is easiest to grab, and the sleeve is ground. Toggle Input on and you should see the raw waveform from your sensor. Adjust Input Level (more-positive values are more sensitive) for an unclipped waveform.

You can play with the Trigger controls to get a stable display if the default isn't acceptable. (I usually prefer Normal mode instead of the default Auto.)

Now go to the Options menu and hit Frequency Counter (or use CTRL+F). Click on RPM and you should be in business. Note that the Frequency Counter window borders can be dragged to resize it, and the readout will grow or shrink to match. Depending on your display, you may need to make it wider the first time you use it, to see the controls at the far right of the counter. The Cyl control works with RPM for use with engines, but it's also for reading RPM from gear teeth. You need to set it to *twice* the number of teeth to get a direct RPM reading.

This setup should give you an independent view of the signal into the Basic Stamp. Daqarta's

30-day/30-session free trial should be enough to debug your Stamp problem. Enjoy!

Best regards,

Bob Masta DAQARTA v5.00 Data AcQuisition And Real-Time Analysis

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Scope, Spectrum, Spectrogram, Sound Level Meter Frequency Counter, FREE Signal Generator Pitch Track, Pitch-to-MIDI DaqMusic - FREE MUSIC, Forever! (Some assembly required) Science (and fun!) with your sound card!

Reply to
Bob Masta

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