Megasquirt technical update...

[russc]

Imon the MS update mailing list. This showed up today about input compatability with the LM-1 and MS:

Megasquirt Integration Note

High-impedance inputs, like those found in the current version Megasquirt fuel computer, can create problems with the LC-1 because the input caps act as dynamic shorts. The easiest fix is to add a 470 Ohm resistor in series with the analog output of the LC-1.

Not sure if it means anything, but the technical reason(w/o looking at the schem) is the there are capacitors to GND on these inputs. At certain frequecy, these caps have resistive characteristics(Xc; X sub c) that can short to GND. Using the resistor inline can minimize this problem, but does completely solve it. These caps are probably used to filter noise on the signal. The real key is to adjust the cap values so they have no effect on the signals frequency range.

I know thats quite technical, but thats the story.

RussC

[Jeremy]

Electronics is not my strong suit, so what does this mean? Is the LC-1 is a bad choice for wideband to use in conjunction with MS? Is the same true for all wideband O2 setups? Does this apply to the MS2 as well?

Jeremy

[russc]

No,
The LM-1 is fine. You just have to be aware of this issure. It really depends on the speed at which you want the input signal to respond. If you want it to respond real rast, then you can do two things, decrease the value of the filter cap and/or use the series resistor(if you can live with the signal attenuation).

Unfortuanatly there is not a one quick fix that is all encompassing. Although there are not alot of output signals from the LM-1 that would go into a MS unit, either MS, MSII. In that regard I and II both use the same PCB, so its just a common hardware issue, not a software issue.

Yes, I believe this would be an issure for any wideband controller that has fast responce signals that are inputed to the MS PCB.

RussC


[Edit by russc on [TIME]1141796441[/TIME]]

[altus22]

The impedance of a capacitor is 1/jwC. To increase the frequency at which the capacitor shorts the signal to ground, you should decrease, not increase, the value of the capacitor.

[russc]

right,
I was writing that post pretty quickly, and didn't get back to edit it. You got to it first.

RussC

[Monotalonawd]

Well, talk about timing!

I just finished installing my LC-1 wideband and some MS wiring in my e28! Seems like I'll have to add one more little resistor. I suppose that's the one drawback of the cheap LC-1 purchase price!

I guess I'll be using the supplied Innovate software at first when comes the time of the first ride!

[DMNaskale]

Imon the MS update mailing list. This showed up today about input compatability with the LM-1 and MS...

This information also popped up on the new Innovate Motorsports online Tuners Newsletter. It is nice to see the manufacturers paying attention to the Megasquirt scene.

Innovate Newsletter

[altus22]

Does anyone know the frequency requirements for the LM-1? If we had that, some quick number crunching could figure out a good value for that capacitor.

[russc]

With the LM-1, the output responce of the O2 is software selectable, so I don't know what frequency that would be. I guess I could get my o-scope out and measure it.

RussC