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Automotive Trigger ??


james89es@...
 

I know this is a little off-subject, but it does relate to using an
oscilloscope. Without going into to details about why I want to do
this, I'll pose the following scenario:

Suppose I want to view the voltage on the primary side of an
automotive coil (12v) and use the #1 cylinder spark plug wire (10-
20kv) as a source of the trigger. I am thinking of taking a length
of wire (18-22gauge) and wrap a few loops around the outside of the
plug wire. I am wondering what kind of signal that would produce.
Would this be some kind of inductance pick-up? Processional
automotive timing lights have a little pick-up that losely clamps
around the plug wire - that's what gave me the idea.

Any insight, short of discouragement, would be appreciated.

Jim

PS: I WON"T be using my vintage Tek scope for this!! I have a very
cheap analog scope that I intend to use instead.


James & Kandy Nunn <jnunn@...>
 

Jim

This will work, you may want to check the voltage spike with your scope before you apply it to your trigger input. I did this quite a few years ago and I found that 3 turns around the spark plug wire produced a 3 to 4 hundred volt spike and with today's electronic ignition systems I would think you would get an even higher voltage.

You could also use a Prox switch to sense TDC on the crank pulley and then use the scope to measure the spark advance over you full rpm range. This would be great for dialing in the distributor for the best performance. I am assuming that the ignition is not controlled by an computer.


Jim Nunn

Suppose I want to view the voltage on the primary side of an
automotive coil (12v) and use the #1 cylinder spark plug wire (10-
20kv) as a source of the trigger. I am thinking of taking a length
of wire (18-22gauge) and wrap a few loops around the outside of the
plug wire. I am wondering what kind of signal that would produce.
Would this be some kind of inductance pick-up? Processional
automotive timing lights have a little pick-up that losely clamps
around the plug wire - that's what gave me the idea.


jeans <jeans@...>
 

Hello james89es,

Tuesday, July 03, 2001, 10:06:14 AM, you wrote:

jyc> I know this is a little off-subject, but it does relate to using an
jyc> oscilloscope. Without going into to details about why I want to do
jyc> this, I'll pose the following scenario:

jyc> Suppose I want to view the voltage on the primary side of an
jyc> automotive coil (12v) and use the #1 cylinder spark plug wire (10-
jyc> 20kv) as a source of the trigger. I am thinking of taking a length
jyc> of wire (18-22gauge) and wrap a few loops around the outside of the
jyc> plug wire. I am wondering what kind of signal that would produce.
jyc> Would this be some kind of inductance pick-up? Processional
jyc> automotive timing lights have a little pick-up that losely clamps
jyc> around the plug wire - that's what gave me the idea.

jyc> Any insight, short of discouragement, would be appreciated.

jyc> Jim

jyc> PS: I WON"T be using my vintage Tek scope for this!! I have a very
jyc> cheap analog scope that I intend to use instead.


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Hi James,
Your idea should work OK but place a pair of silicon
diodes each way across the external trigger input of your
scope. They will limit the pulse that you pick up to about
a volt or so and protect the CRO from spikes. If there
isn't enough trigger voltage, replace the diodes with a
zener diode of a few volts to get a bigger signal.
Don Black.






mailto:jeans@nex.net.au