Dwell reducer circuit for COPs - will this work or not?

[wleung]

Hi Guys,

This question is for the EE/Mechanics out there.

I've been reading up on the COPs conversion as I was interested in it, and was wondering if the dwell circuit needed to be as complicated as the ones in the write-ups?
(i.e. the part that modifies the dwell timing, not the 10,000uF capacitor part)

If the aim is to reduce a ~5ms pulse train to a ~2.5ms (ish) pulse train, would the following positive edge trigger generator shown in the answer for this webpage work?
http://electronics.stackexchange.com/questions/211024/how-to-generate-edge-triggered-pulse
*edit*: Obviously you would change the R2 & C1 values to make 2.5ms

If not, could someone explain why?
(Just a curious engineer who wants to know the answer for this - so maybe I'll go hunt for some Toyota COPs).

Cheers,
Wilson

[wleung]

Appending some information.
A 74LS121 IC chip is probably a better implementation of the same idea - Monostable pulse generator.
(Explanation website: http://www.electronics-tutorials.ws/waveforms/monostable.html - Scroll to 74LS121 Monostable Generator)
Tweaked by a resistor and capacitor in a similar fashion & can be positive edge or negative edge triggered.
Again - not sure if the dwell reducing circuit is supposed to do something else apart from pulse modification.

[hks_kansei]

If you're in Melb I've got one of the dwell reducer circuits from a group buy on here ages ago.

If you want it to test etc you have have it.

[wleung]

Thanks for the offer hks... but I've realised a flaw in my design, and probably won't need it.

The pulse generator would cause it to fire 3ms too early because it's triggering a 2.5ms pulse on the positive transition of the 5.5ms pulse. I'd want to have the 2.5ms pulse align with the negative edge of the original 5.5ms pulse so the spark fires at the exact same spot.

I would need to logically AND the 5.5ms signal with the NOT of a positively edge triggered 3ms pulse to do this, and then the complexity of the circuit starts to approach that of the one proposed in the group buy.

Just wanted to solve the problem with digital circuits to see if it uses less off-the-shelf parts than the version using comparators. I'll probably just try to understand how the group buy circuit works.
I just didn't want to cheat and shove a PIC in there, although that would be just as fun.

Cheers,
W

[wleung]

This is what I was going for: At the moment it has not yet been tested or built - I'll probably do it next time I have free time which will be a while away....

The entire B monostable vibrator may not be necessary - it was just to run the Trigger input through the same propagation delay as the the A monostable vibrator pulse to avoid a temporary spike on the output.
Might be redundant with nanosecond propagation times actually (And thus you can save $2.15 by putting the other coil through the spare monostable vibrator)

The Trigger is AND-ed with the rest of the signal to ensure the firing of the spark matches with what the ECU intended. So the idea is to fiddle with the capacitor on vibrator A to vary the width of the pulse.
Spec sheet says pulse width (seconds) = Rx * Cx.

DigitalDwellReducer.jpg

[manga_blue]

It's worth remembering that dwell time is not the only significant parameter you need to deal with here. The right combination of dwell time and voltage is what you're really after. If you can't get that exactly right then good quality coils (ie genuine Nippon Denso ones, as opposed to generic cheapies) do seem to perform well and survive with serious overcharging anyway.

Check out the table in viewtopic.php?f=55&t=53994

[93_Clubman]

viewtopic.php?f=55&t=53994