Megasquirt V 3.0 PCB ignition control using single vr??
07-17-07, 05:08 PM
#1
V 3.0 PCB ignition control using single vr??
ok guys.... after much reading my head is spinning.... BUT i think i've got a a pretty good grasp on how this process should work. I'm working with a v 3.0 pcb with a MS1 with MSnSE. It's my understanding that a second LM1815 circuit can be built in the proto area to use as a second VR conditioner with no modification to the CAS, or I could simply use the single VR circuit built into the V 3.0 board and cut 2 teeth out of the CAS and also change the wheel decoding parameters in Megatune... ETC. My confusion mostly comes into play regarding exactly which teeth to cut off the CAS... how to stab the CAS correctly and how to properly wire the leading and trailing coils through the DB37. I guess more or less... will I be running all 4 wires from the CAS to the Megasquirt? or just the green and white? Also exactly which pins in the DB37 are wired to the ignition coils???
I hope I explained my questions suficiently and any help would be appreciated.... Lastly is there anhy advantage/disadvantage of the dual lm1815 over the single?
Thanks,
Ken
I hope I explained my questions suficiently and any help would be appreciated.... Lastly is there anhy advantage/disadvantage of the dual lm1815 over the single?
Thanks,
Ken
07-17-07, 08:40 PM
#2
MegaSquirt Mod
The dual lm1815 tends to be easier to get a clean signal with... meaning as long as your G signal is clean, the tach signal is clean. It's a lot easier for the code to look for an extra tooth than it is for it to find one that's missing.
Having the missing tooth there makes it a bit easier for noise to cause a problem.
You can cut any two teeth from the CAS as long as they're opposite each other, and allow enough adjustability in the CAS's range of motion to set proper timing.
After you cut the teeth, the easiest settings to use are 1,3,7,9 for the wheel decoder with a trigger angle of 55-60 degrees. To stab the CAS in this configuration, you line up the third tooth after the missing with the VR sensor, and stab it, taking care to make sure that tooth stays lined up.
You don't need all 4 wires from the CAS unless you're using both the Ne and G signals from it. If you cut teeth, you only need 2 wires.
As for the pins on the db37 for the ignition coils, that's up to you. You have to put pullup resistors on the LED's, and then wire the negative lead of each of the LEDs to a spare pin on the db37, and then wire your harness to use them.
Ken
Having the missing tooth there makes it a bit easier for noise to cause a problem.
You can cut any two teeth from the CAS as long as they're opposite each other, and allow enough adjustability in the CAS's range of motion to set proper timing.
After you cut the teeth, the easiest settings to use are 1,3,7,9 for the wheel decoder with a trigger angle of 55-60 degrees. To stab the CAS in this configuration, you line up the third tooth after the missing with the VR sensor, and stab it, taking care to make sure that tooth stays lined up.
You don't need all 4 wires from the CAS unless you're using both the Ne and G signals from it. If you cut teeth, you only need 2 wires.
As for the pins on the db37 for the ignition coils, that's up to you. You have to put pullup resistors on the LED's, and then wire the negative lead of each of the LEDs to a spare pin on the db37, and then wire your harness to use them.
Ken
07-17-07, 08:41 PM
#3
look thru the thread I started labelled "stabbing the cas" or something along those lines, if you havent read it already it shoudl help you. Have you looked inside your CAS yet? There are two wheels... the first one has 2 teeth spaced 180* apart, and the second one (below the first) has 24 teeth, spaced evenly (so 15*). You would need to cut 2 teeth out of the bottom wheel, and it doesnt matter which two as long as they were 180* apart (opposing). Most of the ones i've seen have had it done spaced between the upper wheel's teeth, just cause its easiest to get a dremel or your tool of choice in there. Now, this missing tooth will serve as a marker for when the megasquirt needs to start re-counting to figure out spark timing and stuff, and serves as a reference point for the spark.
I used a second LM1815 because it seemed like a cleaner way of doing it to me, I didnt need to modify the CAS that way, I had room on the proto area of the v3board to build it, and from what I remember reading, it got a much clearer, noise-free signal than a missing-tooth wheel.
I used a second LM1815 because it seemed like a cleaner way of doing it to me, I didnt need to modify the CAS that way, I had room on the proto area of the v3board to build it, and from what I remember reading, it got a much clearer, noise-free signal than a missing-tooth wheel.
07-17-07, 09:14 PM
#5
thanks for the replies guys... I'm pretty sure I got the basic idea here. I have all the components to build the second LM1815 circuit, but I'm just not so confident in my abilities to do so. Truth be told I bought the MS pre-asembled from another forum member, which has saved me alot of time but also may have shortchanged myself. Not getting the first hand experience with all the details of the board. I wouldn't mind having the cleaner signal from the second LM circuit... if someone could point me to a little instruction in how to mate it to the V 3 board. I have the dual LM circuit schematic file saved on my desktop, and I understand that I only need the right side of the schematic but I'm not sure how all this joins to the existing components on the V 3 board.... any guidance?
07-17-07, 09:22 PM
#6
well, if you isolate the right side, you'll see that it only has 4 things connecting to it from outside. Theres 5v, ground, the signal from the 2nd sensor, and an output to the MS1 chip (pin 11 IIRC). You have 5v and ground right above the proto area already.
