Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!spool.mu.edu!olivea!uunet!world!jon_sree From: jon_sree@world.std.com (Jon Sreekanth) Newsgroups: sci.electronics Subject: Re: Inductive pickups. Message-ID: Date: 7 Jun 91 03:59:24 GMT References: <1970@ole.UUCP> <5170138@hplsla.HP.COM> <1991Jun6.151435.484@otago.ac.nz> Sender: jon_sree@world.std.com (Jon Sreekanth) Organization: The World Lines: 30 In-Reply-To: grahaf@otago.ac.nz's message of 6 Jun 91 15: 14:34 NZDT In article <1991Jun6.151435.484@otago.ac.nz> grahaf@otago.ac.nz writes: > 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 Well, I actually got to thinking about this in context of a 'transportable trip computer'; something you could use on rental cars, for example. Then rather than messing around under the hood, you could plug the sensor into a (still messy but more accessible) cigarette lighter. Of course, being a tacho indication, not a speedometer indication, is a fatal flaw. Regards, / Jon Sreekanth Assabet Valley Microsystems Fax and PC products 346 Lincoln St #722, Marlboro, MA 01752 508-562-0722 jon_sree@world.std.com