sje@xylos.ma30.bull.com (Steven J. Edwards) (06/04/91)
In article <1974@ole.UUCP> ssave@ole.UUCP (Shailendra Save) writes: > From article <JON_SREE.91May31225851@world.std.com>, by jon_sree@world.std.com (Jon Sreekanth): >> 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) >> lighter, don't you see noise correlated with the spark plug firing >> on top of the 12V ? Can that be used ? >> > If I wanted a transducer for a tachometer, I would. I meant > automobile speed when I said speed. Sorry about that. For the > tach, I *am* using pulses from the primary of the coil. (A little > cleaner and easier than the cigarette lighter) > Good idea though. I believe that most cars manufactured in the past decade that allowed cruise control as an option already have an electric pulse signal terminal somewhere in the back of the speedometer housing. This was true of a 1981 Volvo in which I installed cruise control, and the instructions for the generic cruise control electronic module seemed to indicate that this was a standard feature. It is much easier to use this as a signal source than to fiddle with the driveshaft or with transmission cable mechanical linkages. == Steven J. Edwards Bull HN Information Systems Inc. == == (508) 294-3484 300 Concord Road MS 820A == == sje@xylos.ma30.bull.com Billerica, MA 01821 USA == "That Government which Governs the Least, Governs Best." -- Thomas Jefferson
jgd@Dixie.Com (John G. DeArmond) (06/04/91)
sje@xylos.ma30.bull.com (Steven J. Edwards) writes: > I believe that most cars manufactured in the past decade that >allowed cruise control as an option already have an electric pulse >signal terminal somewhere in the back of the speedometer housing. Actually not. Most american cars (as of my tour of dealers last year) still use electromechanical cruise control that involves having the speedometer cable pass through the unit. For speed pickup, you have 2 easy solutions. If your car is manual shift, you can simply use the spark signal from any convenient point. Does not work for automatics because of torque converter slip. As a reference point, I built a cruise control for my 280 and used the spark signal with great success. Failing that, you can install a pickup like the aftermarket units such as sears and penneys sell. This involves glueing 2 magnets to the drive shaft and positioning a coil nearby. for magnets, you can get samarium- cobalt magnets from Rat-shack now for a couple of bux that are very powerful. Strong magnets are needed to allow a lot of clearance with the pickup. For the pickup, you can either order a replacement part from Sears or Penneys or you can use the solonoid coil from something like a washing machine water valve. Back when I was building custom cruise controls for Z-cars, that's what I used. I could get a friendly appliance repairman to save me all his defective valves. Simply pass an appropriately sized bolt through the core of the coil to make a pole piece. I developed a bullet-proof method of attaching the magnets to the drive shaft. Mine have been on my Z for 10 years. In addition to the magnets, you 'll need some 1" fiberglass ribbon and some 5 minute epoxee. I get my ribbon in rolls from an electric motor repair shop. They use it to wrap windings. Two magnets 180 degrees apart seem to be optimum. To attach them, simply stick them to the drive shaft. Then impregnate about 2 feet of fiberglass ribbon with the 5 minute epoxee. Wrap this ribbon IN THE DIRECTION OF ROTATION around the magnets, smooth and allow to harden. Be sure to use the 5 minute clear epoxee. The real stuff that takes hours to harden is too hard and will fracture from heat stress. The 5 minute stuff stays somewhat flexible. The waveform from this pickup looks quite similiar to the bipolar sawtooth characteristic of variable reluctor ignition triggers. It is best detected with a slope-sensitive zero crossing detector that triggers when the waveform crosses the baseline. John -- John De Armond, WD4OQC | "Purveyors of speed to the Trade" (tm) Rapid Deployment System, Inc. | Home of the Nidgets (tm) Marietta, Ga | {emory,uunet}!rsiatl!jgd | "Vote early, Vote often"
johne@hp-vcd.HP.COM (John Eaton) (06/05/91)
>>>> > >For speed pickup, you have 2 easy solutions. If your car is manual >shift, you can simply use the spark signal from any convenient point. >Does not work for automatics because of torque converter slip. As a >reference point, I built a cruise control for my 280 and used the >spark signal with great success. ---------- When my old after market cruise control gave up the ghost I replaced it with a newer model. The old one had the magnet on the drive shaft while the new one had a single wire that plugged into an unused terminal on my electric spark control. Even with an automatic transmission it does a reasonable job at speed control. It's not as good as the magnet but I can live with it. I couldn't figure out how they did it either. John Eaton !hp-vcd!johne
rambler@pnet51.orb.mn.org (Dan Meyer) (06/08/91)
Just for the record, I had a cruise control that used an ignition coil pick-up
in an automatic transmission car, and the tourque converter had no lock-up
clutch like many new cars, and the results were entirely acceptable. the
speeed of my car varied a couple of miles per hour, but it was really no big
deal. I learned to set the highest desired speed on the downhill sections of
highway, and away I went.
-- Dan
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