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Old 06-11-2010, 09:26 PM   #21 (permalink)
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I didn't have a coil of wire for those. I used a magnetic reed switch. The north pole would pass by the switch, and close it. Then the north pole got far away enough for the switch to open. A short amount of time would pass, then the south pole would do the same thing. The magnet would then completely rotate around the driveshaft, and come back to do the same thing.

I didn't capture that, I drew it. I rolled the truck very slowly to hear what was happening, at a rate that I could distinguish the two pulses (I had a speaker hooked up to 12v through the switch).


My next try is going to be a "bead" of glue on the back of the speedometer (the part that spins with the wheels). When the bead rolls around, it pushes on the lever of a micro switch. I think it spins slowly enough that it should work.

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Old 06-11-2010, 09:29 PM   #22 (permalink)
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...mechanical speedometer cables typically rotate at about 1000:1 ratio, as I recall, so that they could measure 'tenths' of a mile.
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Old 06-11-2010, 09:59 PM   #23 (permalink)
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I spun the input and watched for it to move 1/10 of a mile (120 Revs), then multiplied that by 10 to get revs/clocked mile, then multiplied by 1.22 (my tires are oversized) and got 1464 pulses/mile.

At 70 MPH, that is 7/6 miles/minute, or 1464(7/6) per minute. 1708 pulses/minute= 28.5 pulses/second.

29 HZ. I wonder if the switch will work. I imagine that it will, but the question is for how long.

If that wears out, I think I will try a switch from an old telephone. The kind with the two strips of springy metal held together with insulators, and when they are pushed on (or not pushed on) they have contacts that come together.

Like distributor points. Hmm, I could use those, too.
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Old 06-12-2010, 01:10 PM   #24 (permalink)
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That experiment seems to have failed

Seems as though a speedometer cable is not meant to have any load, so even the little tiny bit of resistance the micro switch put on it, the speedo jumped wildly around (remember the pulsing of the speedometer needle [on old cars] at low speeds? like that, but a lot more).
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Old 06-12-2010, 01:31 PM   #25 (permalink)
dcb
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I have the gear sensor in hand, don't know if I will get to an experiment real soon though. I'd like to put it on the rabbit with a guino and see if I get a speed signal anyway (haven't figured out fuel consumption on the tdi yet)
here is the pinout, it might be cleanest to point it at the inside spokes on the rear wheel (if steel wheel), the front inner hub might not have clean protrusions or too many small gaps. It will make a lot of clicks per mile though, which is normally a good thing, but I might have to tighten up the vss parameters in the guino or revisit the algorithm.

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Old 06-12-2010, 06:20 PM   #26 (permalink)
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...truly "mechanical" contact is NOT a good idea because "friction & wear" will doom it to failure, sooner or later.

...magnetic or inductive "sensing" is the preferred method. However, the problem with magnetic is that eventually you end up collecting a "ball" or iron filings and dust. The inductive method is what most automotive applications use.

..."optical" sensing works, but engine oil vapors eventually stop them from working reliably

Last edited by gone-ot; 06-12-2010 at 07:15 PM..
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Old 06-12-2010, 07:13 PM   #27 (permalink)
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well, if the thing in post 25 can go 100k without needing to be unboogered, then I'll call it a win If it is pointing at the wheel spokes from the inside, it should be real easy to see & clean anyhow.
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Old 06-12-2010, 09:21 PM   #28 (permalink)
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Today I tried something similar to the speedometer switch. I put a bead of jb-weld on the part of the rear end that bolts onto the drive shaft, and put a roller micro switch on that, so as the bead passed by, it would click over.

Once I finally got it configured and adjusted, I went and tested it with the MPGuino. It seemed to work, but it was not giving linear readings. Yeah, not linear. It would either read fine at low speeds (20 MPH) and too fast at higher (45, the guino said 70), or it would read slow at slow speeds (20, but read 13), and fine at 45.

Needless to say, I think I will abandon high speed micro switches


This is looking interesting again. First, it is cheap. Second, it is meant for sensing speed, and third, it is magnetic and should hopefully be more reliable than mechanical or visual switches.

I'm sure someone could tell me how to implement it with all our honda people
Does that work with a magnet or lump of ferrous material? What is the pinout? Posative, ground, and VSS?

That would be great

Edit: Oh, dcb, I just looked at the thing in post 25 again, is that the same thing I am pointing to on eBay? If that is the case, I could point it to a part on the driveshaft (I have aluminum wheels)

Last edited by usergone; 06-12-2010 at 09:27 PM..
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Old 06-12-2010, 10:02 PM   #29 (permalink)
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re: ebay, I don't know anything about that sensor. It may need a rotating magnet to work. The one in 25 has a built in magnet and can sense steel lumps passing by.
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Old 06-12-2010, 10:24 PM   #30 (permalink)
I have to start over?
 
Join Date: May 2010
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Big inefficient truck - '94 Dodge Ram 2500
90 day: 12.1 mpg (US)

Honda Civic - '84 Honda Civic DX Hatchback
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I just looked at the datasheet for that gear sensor. I must admit that I can figure out most electronics, but my weak spot is semiconductors (sort of). What does "output type: sink" mean? does that just mean that it puts out its supply voltage whenever the lump goes by?

It looks like it would work perfectly on the input of the rear end, because there is a square shape that should give 4 pulses/revolution.

BTW, thanks guys for sticking with me and giving your time and knowledge in this

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