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Unread 16-01-2005, 20:52
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Al Skierkiewicz Al Skierkiewicz is offline
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AKA: Big Al WFFA 2005
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Re: Hall Effect Sensor.

Sparks,
Sorry this is a little late. I have been looking at the sensor and page 9 is a discussion of the output vs. direction. If the gear is moving in one direction the output will rise from a low state to a high. If the gear is moving in the other direction, the output will move from a high to a low. This is data that I don't think could be useful other that scoping the output while rotating the shaft by hand. The suggestion I made earlier (thanks Greg for the corrected waveform) requires two sensors mounted so that the pulses overlap by 90 degrees (electrical degrees that is). You can see that rather easily in Greg's waveform that the top pulse leads the bottom by some amount. If the direction were reversed, the top pulse would lag the bottom pulse by the same amount. If you were to then compare the pulse trains by sampling when the top pulse goes from low to high, and determining the value of pulse train two, you could determine which direction you were turning. (If pulse two is already high when pulse one goes high you are turning in one direction. If pulse two is low when pulse one goes high you are turning in the other direction.) This is easy to do in software, (don't ask me how) and requires about four gates as I remember, in logic hardware to decode. The Hall effect is actually a pretty neat little package in that it uses two sensors at right angles to each other, to cancel out errors and temperature problems automatically. Please note the restrictions on gear tooth specifications when using and positioning the sensor.
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Al
WB9UVJ
www.wildstang.org
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Storming the Tower since 1996.