Too bad this isn't 1960 and the Ed Sullivan show was on Sunday nights because the presenter is a much better comedian then engineer. His escapades would go over quite well with dancing bears and guys who spin plates on poles.
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However, he'd be tossed out of, and banned, from any university electronics laboratory for his foolishness.
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Suggesting using a resistor divider to reduce direct AC mains to feed a microcontroller is downright stupid verging on criminal.
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The way you measure ultra high DC voltages is with a electrostatic voltmeter.
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https://en.wikipedia.org/wiki/Electrostatic_voltmeter
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I bought a ESH model 600085 at a surplus sale for $5 that will measure 5, 10, 15, or, 20kV. Other then testing it in a real electronics lab, I've only used it once to measure the high voltage for an night scope (starlight scope) tube power supply.
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However for measuring the ignition voltage for anything other then a model airplane engine, which uses a 1.5V glow plug, one needs something like either the?gizmo made from plastic with a screw adjustable gap to measure the ignition/spark voltage, however this measures the voltage under "no load."
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Or the Leslie unit I mentioned earlier which actually shows you how strong the arc is with the engine running.
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When the cylinder rises during the power stroke, the 'air' pressure increases, if you have an engine with 10:1 compression, then your pressure when the spark occurs would be 10 X 14PSI, 140PSI.
140PSI = ~ 7240 torr.
see the graphic at
http://www.highvoltageconnection.com/images/paschen-curve_clip_image002.jpg
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The chart maxes out at 720 torr and shows the voltage required to be in excess of 70,000V. [I have doubts about this graph but don't feel like working out the math this morning.]
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Wiki goes into Paschen's law in quite a bit of detail.
https://en.wikipedia.org/wiki/Paschen%27s_law
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All of this is interesting from a theoretical angle, but the practical aspect is simple:
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"Just because your ignition system produces a spark/arc in a spark plug outside the engine does not mean it will produce a spark in the engine under compression."
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I've seen this in Honda CB350s, 1968 and 1969 stock VW bugs. The ignition coils in the Honda twins was located where they were heated by the engine, I never had a hard failure but I could tell when it was time to replace one when the power dropped way off and the engine sounded funny, both ignition coils never failed at the same time so the power was really imbalanced between the cylinders. I limped home from Mason Ohio [near Kings Island] to Lexington one night sweating "Will I make it home...."
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VW coils just failed for the fun of it. West German manufacture wasn't quite as perfect as they'd have liked for you to believe.
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I learned more about ignition systems then I wanted with those vehicles. I've never had an ignition coil/system fail in
Chevy Nova [My wife's when she was my girl friend. Car died when someone t-boned it in a parking lot. Bummer]
Subaru [two cars, 1980 station wagon, 1984 compact]
VW transporter van with Porsche engine
[I have no idea why a very similar engine never experienced a fuel pump failure or ignition coil failure.]
Toyota [3 cars]
Ford [1 car we put over 200K miles on.]
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I did have the ignition coil fail on a Plymath Omni, about a month before the engine decided to emulate a grenade. [Way too exciting at 80MPH on the Mountain Parkway at 3:00AM. You've never lived until you have parts of the engine come through the hood right before your windshield is covered in oil and coolant. Loads of unfun.]
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[I always carried a spare fuel filter, fuel pump and ignition coil. <and fan/generator/ belt> for the VWs. I've changed the fuel pump and ignition coil by feel in pitch black dark out in the boonies more times than I care to remember. Yea for a person who collects flashlights it was silly not to have one, but the batteries were always dead when I needed the light. I finally got smart and made a 12V trouble light with 20 feet of wire, a fuse and power port to the battery and never had a fuel pump or ignition coil go bad again.]
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A dying ignition coil can produce what appears to be a very strong arc in a spark plug outside the engine and not work or sort of work in the engine.
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Sort of work to mean, rough idle, stalls when you give it gas.
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Modern automotive/light truck ignition coils are extremely reliable.
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Briggs and Stratton lawn mower ignition coils not so much.....
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Real mechanics with real garages with real test equipment designed for cars often have specialized oscilloscopes that will display the ignition voltage. It's worthwhile getting a glimpse if you have a friendly mechanic.
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I would never consider trying to build an adaptor to allow me to see the ignition voltage waveform on my DSO. One could probably salvage the ultra high resistance resistors from cold war civil defense ion chambers and add plenty of diode protection clamps but I'll let others fry their DSO when the Leslie ~$20 device works very well.
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BTW I have no business relationship with Leslie, I'm just a very satisfied customer.
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For the really brave...[or foolish]
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I have no idea if the device will work or fry your scope.
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Ya pays your money and takes your chances. [not me.]
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Oh changing the two drive belts was amazingly easy, took two hours, mainly because I removed the pulies and lubricated them [one bearing will need replacing sooner then later, it's on order] and cleaned the space under the deck, used a wire brush to remove some rust and painted it with a high quality epoxy paint, and I blew dead grass bits out of 'everywhere.' I also added a kill switch to the seat, get out and the engine shuts down. The twins are a bit careless. I do not want anyone to lose a foot. [Yea I'm paranoid.]
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