MembersPage/MattiasSandgren/MrideCarForTwo/Trigger (2007-07-25 02:31:50)
[Start] [[Trigger] [[FuelInjection] [[Display]

Trigger

The plan was to use a wire connected to the negative pole of one of the ignition coil primaries.

The voltage at igncoil primary is a bit high (also, dangerous to your health and your equipment):

As you see, it has 2 falling edges, a small 14=>2V and a big edge +200V =>14V

Concerns

Suggestion

HALL

With HALL setup, it's perfect if the signal goes below 1V, than above 3V. Should be rather easy. The 1/58.5 voltage divider from 270k and 4k7 is good, keep appr those values in case of HALL

VR

With the controller primary_trigger=VR, the signal must go below 0V to trigger. Also, the falling edge is detected (not possible to detect the rising edge). Because there are 2 falling edges, this might cause some problem with unsuitable bias hardware. With good setup, the 14V=>200V will arm the adaptive-threshold circuit and only the 200V=>14V edge will be sensed. With VR I would try the following setup as a starting experiment:

Capacitive coupling from sparkplug wire => VR input

With VR input (at least on suzuki swift of MembersPage/Gabor ), we've seen success with a few (3..5) turns around a High-Voltage spark wire (that is transformer secondary). No galvanic contact, of course. The "capacitive coupling" was enough to trigger the circuit reliably. Note that the signal is small (maybe just 50..100mV): it worked without primary trigger pullup resistor. Currently the R30= 18..22k internal pullup (now standard) of the VR input is in the way for this application (it's ment to make the input non-sensitive to noise, but in this application we want to sense "noise"). A strong 470 Ohm pulldown to GND or a weak (appr 39k, but this would need to be adjusted for near 0mV +- 40mV DC) towards -8V could work, but the internal pullup might need to be removed or the sensing wire might need to follow the sparkplug wire along a longer, 20..40cm section to get a stronger coupling. Experimentation might be needed (scope is almost essential)

Also, keep the sensing wire away from all other sparkplug wires (so only the chosen spark is detected without interference from other spark-wires).


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