I would like to data log commanded spark events for my vehicle. It uses a Distributorless Ignition System which consists of a engine control computer, a control module, and a coil pack. The coil pack is fed 12v and has control wires. When a control wire is brought to ground by the control module, current can flow through a coil primary winding. The control module holds the ground for a ECC demanded dwell at which time the ground is raised, causing the coil to discharge.
I want to monitor when each control wire is being held to ground.
My monitoring device can take a 0-5v DC input. Do I need to be concerned with the current in the primary circuit that I will monitor voltage on? Is there a circuit design, or a discrete component that will scale the
12v on/off signal into a 0-5vDC output I can push into my DC input? This will need to operate fairly quickly.
You have to deal with very high voltages(hundreds), when the ground connection opens. I would advice 100k to 1 megohm in series with two 4 volt zenerdiodes anti parallel, to clamp voltage to 4 volts. to make more of a divider, shunt 30k accross the diodes and a small capacitor of 200 pf.(the last to stop capacitive coupling accross the
100k to your input). Then maybe your electronics will stay alive :)
Perhaps I didn't describe my intention fully or am understanding what I see incorrectly.
In the case of my ignition system, an electronic control module receives 12v. A pack of 3 coils receives 12v (6 cylinder motor, wasted spark system). Each coil primary thus has 12v but the primaries are not grounded. Ground is achieved by a switch inside the electronic control module which provides a ground to the primary of each coil as necessary.
Note that these are ignition events, thus such events occur in hundreds of microseconds.
My understanding is that When the electronic control module brings a coil primary to ground, current will flow through the primary. When the ECM lifts the ground, an electrical field in the primary will collapse creating a large induced voltage in the secondary winding of the coil.
If I just want to monitor when the ECM drops a line to ground, and then lifts it again, will the voltage not be limited always to 12v at the primary?
My idea.. thus far is to create a voltage divider that sits in parallel on the control line. When the ECM drops the control line to ground, my voltage divider will output 4.5v. When the ECM raises the ground, my voltage divider will output 0v.
New idea, that I used aaCircuit to show.
Could I not use a 5vdc power source for my input to my data logger. Then have the sensor ground for that input be tied to the ground on the primary control wire to the Coil? Thus when that becomes grounded my 5vdc flows through my other circuit?
As soon as the ecm line gets diconnected from ground, a huge induction voltage is sitting on your device, blowing it to pieces. You need the protected divider I spoke of. The ignition coil acts as an auto transformer, and as soon as you break the current, you get a big volage across the 12volt winding. Not as bad as at the spark plug(thousands of volts), but bad enough. Thats why they use ~800 volt transistors to do the switching in the ecm unit.
O.k. Revising. Idea is separate 5 v supply for data logger and have it's sensor ground tied to the switched ECM coil ground. Will this work? See diagram below. Note Channel 1 on data logger. C1+ receives +5vdc
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