Timeline for Measuring and conditioning ignition coil secondary signal
Current License: CC BY-SA 3.0
23 events
| when toggle format | what | by | license | comment | |
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| Jul 12, 2018 at 17:56 | history | tweeted | twitter.com/StackElectronix/status/1017467757300998144 | ||
| Jul 12, 2018 at 16:00 | comment | added | Lelesquiz | I'd use a coil around the secondary to measure the ignition current. You can size the coil so that you get a signal that suits your voltage levels. | |
| Jul 12, 2018 at 10:51 | vote | accept | John M | ||
| Jul 12, 2018 at 10:48 | answer | added | David Planella | timeline score: 2 | |
| Nov 29, 2017 at 12:19 | comment | added | John M | But then again, as you already mention, working peak voltages can be much higher than the depicted 2 kV (the picture is just for example's sake, not actual voltages from this car), which I don't know whether the ACS720 could actually survive. After a quick search, I haven't found any application note or anyone actually using the chip for that purpose. I'm currently leaning towards using a capacitive clamp and a capacitive divider as the first stage of attenuation to a voltage that can be handled by a Schmitt trigger. | |
| Nov 29, 2017 at 12:18 | comment | added | John M | If I had another way available that did not require handling HV, I would definitely use it. But I don't see much difference in measuring voltage vs. current in this particular case: once the signal is conditioned and brought to digital levels, they would both indicate that ignition is happening with a '1'. I'm not interested in measuring burn time, just the start point of the spark for timing purposes. The only advantage I can see is that the ACS720 could potentially be connected directly to the secondary, without the need of a capacitive/inductive probe. | |
| Nov 29, 2017 at 12:17 | comment | added | John M | @JimmyB: Thanks again for the replies. Just to be clear of why I need to measure on the secondary: I only have two signals available: a) RPM: from the primary, 4 pulses per distributor revolution, which correspond to the pulses sent to each one of the spark plugs; b) Spark #1: from the secondary, 1 pulse per distributor revolution, corresponding to the single pulse sent to spark #1. Signal Spark #1 is the only way I've got to synch. There is no other way and I don't really need the RPM signal for timing purposes. | |
| Nov 29, 2017 at 11:59 | comment | added | JimmyB | Using current as an ignition indication has the advantage of a) being more of a 1/0 signal - current is only flowing when and as long as the actual spark is there, it's 0 at other times and b) for the same reason indicates precisely when the actual ignition inside the cylinder begins. - Btw, to measure timing advance you will need some reference of the crank shaft angle anyway, don't you? | |
| Nov 29, 2017 at 11:49 | comment | added | JimmyB | As to the secondary voltage, you may want to consider an open circuit case (bad contact, disconnected spark plug/cable,...), in which you will likely see much higher peak voltages than those 2kV under normal operation. | |
| Nov 29, 2017 at 11:47 | comment | added | JimmyB | Measuring on the primary side does, of course, require some way of synchronizing to the distributor or some other signal source to infer the cylinder which is currently igniting. When measuring the 12V system's voltage, some signal processing (analog high-pass + digital post-processing?) needs to be done but it's absolutely doable; you still have to somehow infer the active spark plug though. | |
| Nov 29, 2017 at 11:43 | comment | added | JimmyB | Imho, the main problem is in handling the high voltage of 3kV+. I would try to avoid that as much as possible. In contrast, connecting to 12...20V and stepping it dow to 5 or 3.3V is no problem at all. The ACS720 is a hall-effect current sensor which converts the current through it to an easily handled analog voltage between 0 and Vcc, and it seems to be semi-safe for voltages of about 3kV on the current measuring path. | |
| Nov 27, 2017 at 17:02 | comment | added | John M | c) Ack d) Wouldn't I have to attenuate the signal in this case as well? If so, then it would it not still be easier to measure the higher amplitude, periodic and longer low frequency pulse from the picture? Listening to high frequencies might also lead to false positives. | |
| Nov 27, 2017 at 17:02 | comment | added | John M | @JimmyB, Thanks for the comments. a) The single spark #1 pulses are only available on the secondary side. On the primary side, they are intermixed with the pulses to the 3 remaining spark plugs. Otherwise, I'd happily measure on the primary (which I'm already intending to do to get the RPM signal, but that's a different subject). This is a 70s car, it's all pretty bare-bones :) b) Why would I want to measure the current instead and how would that be easier than attenuating and squaring the input voltage? Would you mind expanding on that and on the use of the ACS720? | |
| Nov 27, 2017 at 16:34 | comment | added | JimmyB | The ACS720 current sensor is spec'd up to 3600Vrms. For a hobby project, this may be enough of a margin. | |
| Nov 27, 2017 at 16:26 | comment | added | JimmyB | a) Can't you measure on the primary side? b) Can you measure the current instead of the voltage? (Should, imho, represent start and end of the actual ignition even better (more 'digitally') than voltage.) c) Inductive coupling seems to be a common way. d) You can also try and 'listen' to the ('high' frequency, higher than 3/60 x alternator's RPM, kHz maybe) noise in the car's 12V system. | |
| Nov 27, 2017 at 15:50 | comment | added | John M | Thanks for the reply. The content of the question should show that I already did some research online before asking it, apologies if that wasn't clear. The reason I posted it was that generally StackExchange sites provide more informed/opinionated answers and discussion than simply doing a Google search. Also, any answers would help others facing the same question along the way! | |
| Nov 27, 2017 at 15:39 | review | Close votes | |||
| Dec 12, 2017 at 3:02 | |||||
| Nov 27, 2017 at 15:26 | history | edited | John M | CC BY-SA 3.0 | added 23 characters in body |
| Nov 27, 2017 at 15:15 | comment | added | Trevor_G | A quick search on line shows many ways to do this, from a special probe designed to hook into your scope, to various hacks that use things like wires wrapped round the spark-plug lead, hall effect sensors, capacitive couplers.. Take your pick. | |
| Nov 27, 2017 at 15:13 | history | edited | John M | edited tags | |
| Nov 27, 2017 at 15:06 | history | edited | John M | CC BY-SA 3.0 | added 508 characters in body |
| Nov 27, 2017 at 14:54 | history | edited | John M | CC BY-SA 3.0 | added 19 characters in body |
| Nov 27, 2017 at 14:42 | history | asked | John M | CC BY-SA 3.0 |