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Transients in Automotive Inductor Signal

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floobydust:
I'm not a fan of the circuit for reasons already mentioned- what happened at 0:47 ? and at 2:53 it double-pulses.
The "ringing" you see at the trace bottom during rise is just EMI on ground and not the ringing on the primary that I was talking about.

SugerSquirrel:
I was thinking that the event at :47 could be noise from a wire moving and being picked up by/from the probe or the noise from the knob I was turning to change the time duration.  And the double pulse I am not sure but since it occurred during the trigger period is it really a double pulse?  Just my thoughts.

Suger

floobydust:
I would say 0:47 looks like a bad connection at the scope probe and 2:53 is multiple triggering. The scope would not retrigger until it is finished its sweep.

As I've mentioned, there is usually a speed/spark gap/engine load combination where these circuits either don't trigger or false trigger. It's not easy to come up with something really solid, that also does not load down the coil. You can trigger on an AC or DC voltage level, polarity, rise time and any combination of these properties.
As I see it, the circuit triggers on a +ve HV pulse, amplitude over around 141VDC (12kV secondary). Any -ve pulse or -ve ringing shut off the transistor.
So if you have an initial primary voltage spike of +300Vpk and after the spark it then it rings and the next is +150Vpk, you will multiple trigger. It's the problem with only picking off the initial HV spike- below that threshold when idling/cranking or a weak battery/compression gives no or missing triggers. If there is (high Q) lots of primary ringing and it multiple triggers which can be OK and expected- if there is a one-shot (debounce) in H/W or S/W afterwards to ignore anything for a few msec after the initial trigger. Do you have that?
It's easier to work on these circuits with a DSO.

SugerSquirrel:
I do not have a one shot in my circuit, neither HW or SW.  I was thinking about that the other day as a matter of fact.  I was thinking of going the software route.  I could start by having one that is say 75% of the period, and increase it until I don't see any false triggers.   I am not sure what a DSO is, can you explain to me what this is?
    Thanks for your continued assistance.

Suger

floobydust:
You can use a second transistor (post #3) or 555 timer as a hardware one-shot. At least 1.5msec for an 8 cylinder engine and you can go longer for 2/4/6 cyl engines. If you need over 8,000RPM ability then shorten the debounce time a bit but who uses a single ignition coil at that speed. You just want to debounce (ignore) until past the end of the burn time, which varies.

If you debounce in firmware, you can trigger off a falling edge to make an interrupt, and then ignore further pulses for an extra say 1.5msec before re-enabling. It depends on your MCU's timer resources.
I'm not sure what you are doing with the signal. You can measure RPM two ways - # pulses over a fixed time period, or measure time between pulses.

DSO- digital storage oscilloscope, the blink blink blink of an analog scope can make it tough to see glitches or extra pulses.

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