I've seen inductive coupling used on the primary side (ie the wire to the points) of the coil for a tacho triggger . On the secondary you can use capacitive coupling by wrapping some foil around an HT lead and adding another capacitor to form a capacitive divider & protect (somewhat) against the high voltage. You can even connect a scope to this arrangement to view the waveforms. I'm not sure an inductive pickup on the secondary side would be too effective as the current is pretty low. Richard P On 26/07/06, Bob Barr wrote: > On Tue, 25 Jul 2006 20:03:01 -0700 (PDT), John Chung wrote: > > >I haven't used a current clamp before so here goes. > >Can the current clamp detect the rpm of the car? Just > >hook the clamp to the spark plug line and use the Hz > >to determine the RPM? Is the clamp sensitive enough? > > > > You wouldn't ordinarily use a clamp-on current meter for RPM > measurements. I don't know if that would even be possible. > > Many automotive timing strobes use a clamp-on inductive pickup to > trigger the flash circuit when one particular sparkplug fires. A > timing mark on the crankshaft is used to set the ignition timing. > > Most tachometers, though, connect across the points and calculate the > RPM from the frequency of the points opening and closing. > > > Regards, Bob > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist