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Old 05-20-2010, 06:26 PM   #11 (permalink)
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I think this device looks promising
1GT101DC Honeywell / Microswitch Industrial Hall Effect / Magnetic Sensors

Tell you what, I need some more chips. I will order one and see how it goes. But in theory you should be able to point it at any rotating lump of metal (i.e. bolt head on cv joint)

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Old 05-20-2010, 07:20 PM   #12 (permalink)
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Hehe... I love taking stuff apart.

I took apart a treadmill, and found that it had a little sensor beside the drive pulley. Took that sensor apart, to find a nice little reed switch. I hooked it up to a battery and speaker (to hear a signal) and tested it up to (I think) close to 50 HZ.

I will now have to zip tie a hard drive magnet to my driveshaft to hear how fast I am going... AH AH AH (the count laugh)

EDIT: Don't worry, I'll put the magnet on the output shaft of the tranny... so the magnet is not 3 inches from the axis...
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Old 05-20-2010, 07:31 PM   #13 (permalink)
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there ya go I still want to play with the honeywell but reeds work well too. Instant might not be solid but should average out.

I would say for hookup (guessing):

(prebuilt)
Code:
12v-[reed]-guino vss
otherwise this might get it (prebuilt has pulldown on vss).
Code:
12v -/\/\/5k/\/\-+-[reed]-gnd
                 |
              to guino vss
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Last edited by dcb; 05-20-2010 at 07:37 PM..
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Old 05-20-2010, 08:25 PM   #14 (permalink)
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Just took it for a test drive. The speaker turned out to be very useful. I took it to about 50 MPH and it worked fine, with one caveat. The waveform seems to be a bit screwy.

Judging by my ear-scilloscope, the waveform is something like this:


Whereas I think I want something more like this:



It would seem that my problem is that the hard drive magnet (or fraction therof) has a strong field on either side, but nut so much inbetween. The fields are both oriented so as to be able to trigger the switch every time one passes by.

This could be solved by just using the (bigger) magnet that was on the treadmill


Oh, BTW, the way I have the reed hooked up now is this:

+9V---reed---speaker---ground
(powered by a 9v battery for this test)
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Old 05-20-2010, 10:11 PM   #15 (permalink)
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After a bit of noodling around with the reed switch and magnet, I got the waveform I want (the second one).

Now it would appear that my next problem is getting the MPGuino!
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Old 05-20-2010, 10:58 PM   #16 (permalink)
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Ah, the joy of DIY. Stuff doesn't work right. Initially, at least.

Took it for a test again, and after pulling over and adjusting, driving, pulling over, etc. The results are this: The pickup either gets the first signal (see above post) reliably, or the second signal intermittently.
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Old 05-22-2010, 03:48 AM   #17 (permalink)
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I'm asking if a different tranny willl bolt up to your car. 88-2000 single cam tranny will bolt up to another honda civic. There are even hydrolic to cable tranny conversions availabke. Say there is a different trim model of your car, swap in that tranny for longer gears.-
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Old 05-22-2010, 12:12 PM   #18 (permalink)
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Actually, changing the tranny is not all too uncommon for this truck (or the cherokee). Usually when someone swaps out the engine, they do the tranny too, because the AX5 (what I have) is not too strong.

However, it seems to me that swapping the tranny just to get a VSS is taking a hammer to crack a nut. Thanks for the suggestion, though.
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Old 06-11-2010, 07:54 PM   #19 (permalink)
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After receiving my MPGuino, I have been trying to make the reed switch work. It is not the best choice. The contacts stuck together in one, and when I replaced that one, the second one had the same problem.

So now I am open to suggestions. DCB, how did that hall effect sensor/switch come out?
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Old 06-11-2010, 09:18 PM   #20 (permalink)
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...a magnet has a North and a South pole. As the North pole passes the pickup a voltage is induced (lets assume its polarity is positive (+)) and then the South pole passes the pickup, so now a negative (-) voltage will be produced. If these two voltages are "read" as absolute voltages (meaning 'sign' was ignored) then you'd "see" a double-pulse like you mentioned.

...how can the absolute voltage be created? by rectification (diodes) or active circuits.

...what did you use to capture (visualize) those pulses?

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