Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!cs.utexas.edu!uunet!comp.vuw.ac.nz!canterbury!otago.ac.nz!grahaf From: grahaf@otago.ac.nz Newsgroups: sci.electronics Subject: Re: Inductive pickups. Message-ID: <1991Jun6.151435.484@otago.ac.nz> Date: 6 Jun 91 07:23:23 GMT References: <1970@ole.UUCP> <5170138@hplsla.HP.COM> Organization: University of Otago, Dunedin, New Zealand Lines: 37 In article , jon_sree@world.std.com (Jon Sreekanth) writes: > In article <5170138@hplsla.HP.COM> tomb@hplsla.HP.COM (Tom Bruhns) writes: > > > ssave@ole.UUCP (Shailendra Save) writes: > > > I am trying to get a signal from the drive shaft of my car > >using an inductive pickup. (To calculate and display speed) > >Before I get under and get dirty, I wanted to know if anyone > >has had any experience with a similar transducer? Can you > > > I've never worked with automobile electronics, so this might be > totally off-the-wall, but ... isn't there enough leakage from the > spark plugs, both as radiated and conducted interference for it > to be picked up ? In other words, if you plug into the cigarette > lighter, don't you see noise correlated with the spark plug firing > on top of the 12V ? Can that be used ? > Ummm. Sort of. But there are two problems. One isn't so much a problem as an easier way. If you look at the voltage across the ignition points in the distributor then you get a nice low voltage, relatively clean signal, BUT it is only related to engine speed not car speed. The gearbox is in the way. If you have an automatic then there is some slippage between the transmition and the engine. If the car is in neutral then there is a signal with no speed at all :). I remember in the late seventies/early eightyies when trip computers first came out, many of the kits used an input from the drive-shaft. This was done with magnets and a Hall-effect device I think. There were four small magnets spaced equally around the shaft and wired in place, the magnets are small enough to not effect the shaft balance. I have no idea of the availability of the kits now but there may be someone with an old one you can canabilise. good luck, Graham.