Nice to see somebody playing with these processors.
I just ordered a Rasberry Pi to fiddle with and make into media box due to it's HDMI out and Bluetooth ability.

Possibly use my phone as a remote.

 

Why is my simple explanation not correct when it states the same as what you typed above in Red?

I agree about the saturation BTW which is in blue.

Without the disconnection, reconnection, none of what you typed can happen. Never did say it remains connected.

So, Connect builds the charge, (matches your green statement) disconnect releases it. (matches your red statement) This is what increases the 12v to 20,000v aproximate.

Not quite sure how it's wrong?

 

If the coil primary side ground (tach wire) is totally disconnected it will fire the secondary the moment the ground connection is broken.
The "tach signal" is only "disconnected" in the sense that the primary ground path is opened. (the gauge wiring is never messed with)

The way you phrase it it sounds like voltage 'builds up' in the coil until it is unleashed.
What you are describing is more analogous to a capacitor where electrons build up on the plates and discharge exponentially when current is removed.

But that is not the case in an ignition coil.
The coil is a transformer.
If the winding ratio were 100:1 and it had 12V in, you would see 1,200V out when the field were collapsed.

The 1,200V is created by the collapse of the 12v electromagnetic field, but it is not a "charge" per say.

 

In a way it is a magnetic "charge" but not an electron charge. There is still "potential", and when it returns to rest the passing thereof through the windings gives the voltage output - in bothe the secondary and the primary.

 

I would agree with that.

What Is the Difference Between an Electric & Magnetic Field? | eHow.com

 

So, that 44 year-old degree in math and physics finally paid off?

 

I'd appreciate it, if it's not too much trouble. I just put the meter on mine, but I don't think it was providing much in the way of useful information.

What size capacitor would you suggest? It's been ages since I've played with capacitors as filters, I don't have a feel for proper sizing anymore.

Coincidentally, I got a Raspberry Pi for Christmas; that's actually what got me thinking about getting back into electronics. It's a neat little machine, I'm working on turning mine into a wi-fi enabled programmable launch control system for fireworks. If all goes well, instead of running around lighting fuses and dodging fireballs, this year I'll be able to sit back with the family and run the whole thing from my iPad.

 

Today got cut short due to the need to pick up a new alternator. Hopefully I can scope it tomorrow.

 

I didn't know you were a Pyrotechnician.
I was into High Power Rocketry for years.
Do you have a LEUP, or is this class C stuff?

 

No rush, whenever it's convenient for you. I do appreciate it.

Heh, I'm only a 'pyro' in the sense that I like to watch stuff burn. This is consumer-grade stuff...it's all legal over in Alabama where my parents have a little lake house, so every Independence Day we all make the local fireworks sellers a little richer and set up our own little show. It's gotten to the point that most of our end of the lake knows to be out on their docks at dusk to watch those nuts down in the cove to see if they blow themselves up this year or not.

 

Here's picture of the input to the coil, the green wire (DG/Y in the schematics). The trigger is at the point the DS-II module fires the ignition, which means it quits taking the terminal to ground, letting it go up. And the scale is 10 volts per division, with ground being two divisions up from the bottom.

As you can see, the voltage goes above 50 volts positive, swings back negative, then positive, and gradually decreases its swings until it it settles in at about 15v for a bit. (It's going for battery voltage even though there is a resistor in the positive feed to the coil as there's effectively no current and with no current there is no voltage loss.) Then the DS-II box grounds the terminal and the voltage swings and then settles down to ground while the coil charges up magnetically, which is the "dwell". (I don't know why the voltage goes ~15v negative after a bit. Do they use a voltage-doubler to effectively hit the coil with 30 volts?) Anyway, it then goes through that cycle for every cylinder.

My point in all of this is that if the sensing circuitry is voltage sensitive you need to have some protection on it as it will certainly see more than 50 volts. In fact, what my scope shows is actually less than w/o the scope because the scope's capacitance, however small, will tend to dampen the swings slightly. So, were it me, I'd put a 25 volt zener across the input with a resistor ahead of it so it isn't trying to deal with the coil's wrath.

 

Ringing like a bell!

 

Yup, that is a perfect example of ringing. Very little damping.

 

Do a little google'ing you will find many examples of how to read the RPM with an Arduino.

I have done it, It's pretty easy, you have to condition the pulse first.

I do have all this info, it's archived, I have abandon the Arduino for better more powerful processors.

The Arduino is a great toy ... And that is exactly what it is, a toy! It will read every sensor on your vehicle with the right interface, however don't plan on controlling anything and read sensors, you'll finds it's limits real quick!

The hard part is getting it off the breadboard and onto boards ...

Order up these parts and I'll give you a schematic for a proper power supply ...
1 DC/DC Converters 1A DC/DC REG 6.5-18Vin 5Vout #919-R-785.0-1.0
1 Metal Film Resistor - Through Hole 0.68Ohm 1/2W 200PPM #279-LR1LJR68
1 Metal Film Resistors - Through Hole 1/2watt 220ohms 5% #594-NFR25H0002200JR5
1 RF Inductors 40µH 2.0A 0.18ohms #871-B82111EC23
1 Rectifiers 200V/1a Rectifier General Purpose #512-1N4003
1 TVS Diodes - Transient Voltage Suppressors 20.5Vso 16VAC 18A #576-P6KE24CA
1 Aluminum Electrolytic Capacitors - Leaded 25volts 220µF Mini Low Impedance #647-UTT1E221MPD
1 Film Capacitors 0.33µF 100volts 5% #871-B32520C1334J
1 Tantalum Capacitors - Solid Leaded 0.1µF 35volts 10% A case .10 LS Radial #74-199D104X9035A1VE3

The last element of each row is a Mouser PN signified with a # symbol.

As soon as I dig up the Gasser tach stuff I'll post it.

O-yea, What software are you using for schematics ... I can probably give it to you in that format!

-Enjoy
fh : )_~

 

Gary, thanks for taking the time to do that. That's an interesting trace...not at all what I expected to see.

Everything I've found so far online is for an optical tach, which isn't really what I'm looking for. I'll keep looking - and anything you're willing to share will be greatly appreciated. I don't actually have any schematic software; I've been fiddling with Scheme-It online, but not seriously. If you have any suggestions for software to fit my budget ($0.00), I'm all ears.