i've been working on bringing the timing system technology up to a higher accuracy for the megasquirt2extra for sequential operation. i've tested a bunch of methods, mounting techniques, and sensor types along with a number of electrical circuits, some i built and some i bought for testing. i settled on this arrangement for my new project engine and have another set to retro-fit to my current engine.
it probably doesn''t look like much in it's finished state but it represents about $500 worth of stuff selected and purchased whenever i found the stuff cheap.
here are the hall effect sensors and 2 channels of signal conditioning.
the crank signal is generated by the paquet green line gear tooth sensor. it's a hall effect type device that has a magnet mounted behind the hall effect component. when a gear tooth made from a ferrous metal rolls past the head of the pickup, it triggers the hall effect. the pickup sends it's signal to a conditioner board that has a comparator chip on it and a potentiometer for dialing in the signal sensitivity from the pickup. that comparator chip develops a 4.4 volt square wave that gets fed directly to the microprocessor on the megasquirt's main board. it runs 35 pulses per crankshaft revolution with a space for a missing tooth that resets the count.
the hall effect device used for the cam shaft is unipolar, positional type that senses the field from the south pole of a neodymium magnet and switches it's voltage state in the presence of that field. mounted to the cam gear, the "flying" magnet trips the sensor once every revolution (every 2 revolutions of the crank) to tell the megasquirt which phase the valve train is in. again i used the same hall effect conditioning board to generate a second 4.4 volt signal pulse that feeds the 2nd trigger input of the ms2's microprocessor. here's the complete timing set in it's final configuration.
i tested the stratified engine components hall effect conditioning board that uses an optoisolator chip to generate the pulses for the microprocessor on the ms2. it works fine but was pretty expensive to be using 2 units. i also tested 3 conditioning boards that i sourced from china that were built for use on electric vehicles in much different applications. in quantity, those were much more economical and available in smaller lots. 2 of those boards used comparators, 1 just used the analog signal from a board mounted specialty hall effect. one of the 2 boards that used the comparator had the sensitivity potentiometer. that's the one i chose. the other comparator type board has both analog and digital output pins and works great, too. the board is a little bit bigger, has a hole for mounting, and 4 pins instead of 3.
here's a blown up pic of the conditioner board i selected.
you can see that it's 2 boards that haven't been cut apart. this little guy will get installed in an enclosure that's installed right onto the timing wiring harness. the module will have 4 wires running from it, a 5 volt supply from the megasquirt board, a ground wire that runs to the common grounding point under the hood, and a signal wire for each of the crank and cam signals.
that's as simple as i can make this high tech timing arrangement. it has super high rejection mode so electrical noise is minimized. it connects directly to the microprocessor so it bypasses all of the on board signal conditioning on the megasquirt which mean i can leave about half of the component parts off the ms2v3 construction. it's also 100% stable way past 20,000 rpm. with the exception of the sensor sensitivity adjustment which will make it easy to dial in the pickups, there are no adjustments that have to performed to make the electronics work. that makes it "plug and chug" simple, something that gave me fits when i was trying to get my turbo3 running on the megasquirt.
the ms2 using the variable reluctance pickup requires that you fiddle and fart with the sensitivity and hysteresis pots on the board inside the controller to get the timing signals to "sync." that task is different from one megasquirt installation to the next and it's a tedious step which took me hours to perform the first time. also, there's the possibility to get the 2 wires on the v/r sensor backwards which causes more hassles. another problem is that a variable reluctor can generate a low (.5 volt) signal at low speeds and generate a huge signal (70 volts) at 7200 rpm. that big signal has to be conditioned on the ms2 board so that it doesn't exceed the processor input voltage of 5 volts. when you accomplish that, it also puts the low end signal in the "mud" - below the useful level, which in turn gives you false triggers on the timing and those make you lose sync. if you were unlucky, the lost sync and false triggers could fire a coil at an inopportune time and damage the engine.
i'm very sure that my technique is very reliable, 100% stable, and mostly idiot proof in a "set it and forget it" kind of way.
megasquirt is fun!
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then on the other hand, if you don't blaze your own trail you have to look at the trash the others throw on the path.