NeilP
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| posted on 8/4/07 at 06:41 PM |
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Speedo wierdness...
OK - Working on the basis that the geniuses of the site have been bolstered by an overdose of chocolate (it would be bad parenting to let the kids eat
that much, etc., etc.) and therefore can solve this in a tic.
Telemetrics speedo using a magnetic reed switch as the pickup. 5 magnets on the input flange to the rear diff, gap between the sensor and the magnets
c. 0.5mm and all lined up dead straight. Have tested the switch and it is definitely working as the magnet passes underneath (but only when the magnet
is absolutely bang under the sensor).
Speedo picks up to about 15mph and then as the propshaft gets faster it just drops to zero. Wiring is an ignition feed to one side of the sensor and
then returns to the white/black wire on the speedo - Everything else on the speedo works just fine (as far as I can tell, odometer, lights etc.)
I think it's a knackered sensor but thought I would seek second opinion(s) first before ordering new bits / ripping things apart 
p.s. Magnets all the same way and diff isn't wobbling!!!
[Edited on 8/4/2007 by NeilP]
If you pay peanuts...
Mentale, yar? Yar, mentale!
Drive it like you stole it!
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stevebubs
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| posted on 8/4/07 at 08:47 PM |
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1) How far away from the prop is the sensor? Normally needs to be quite close
2) How flexible is your mounting bracket? Needs to be really stiff or the vibration will cause issues...
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Mr Whippy
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| posted on 8/4/07 at 09:03 PM |
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I have eaten so much choc I feel sick
Fame is when your old car is plastered all over the internet
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NeilP
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| posted on 8/4/07 at 09:07 PM |
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Sensor is right on the prop and magnets (prob. less than 0.5mm gap between them). Vibration could be an issue - I'll need to have the cover off
and get someone to drive whilst I tinker...
Any other thoughts, you lot (other than not wanting to think about choc!!!)?
If you pay peanuts...
Mentale, yar? Yar, mentale!
Drive it like you stole it!
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turbodisplay
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| posted on 8/4/07 at 09:22 PM |
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If it is a reed switch it would not cope with a high frequency, as it is a mechanical design. Is it really a reed switch?
Darren
[Edited on 8/4/07 by turbodisplay]
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NOTE:This user is registered as a LocostBuilders trader and may offer commercial services to other users
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mark chandler
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| posted on 8/4/07 at 10:45 PM |
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try junking the reed switch and using an old ABS sensor, nothing to wear out in those.
Regards Mark
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jambojeef
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| posted on 8/4/07 at 10:56 PM |
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Reed switches are good for up to about 150hz for the really fast ones.
I think you might be reaching limit of how fast it can switch...
Really u need a hall effect sensor but you need one that gives the right ouput, some give sine wave outputs and others square wave.
rswww.com do a digital output sender for about £28, would b cheaper elsewhere but theyve got all the data sheets too
Geoff
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RazMan
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| posted on 9/4/07 at 09:24 AM |
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I would guess that the reed switches are running out of puff. How about removing alternate magnets and reprogramming the speedo to suit?
Cheers,
Raz
When thinking outside the box doesn't work any more, it's time to build a new box
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