Dual VR V2.1

[jbelanger]

What are each wire connected to? Black, orange, yellow, red? And which alligator clip (yellow, red) correspond to which probe? I can't see from the picture.

[rccardude04]

What are each wire connected to? Black, orange, yellow, red? And which alligator clip (yellow, red) correspond to which probe? I can't see from the picture.

Sorry,

Probe A + to orange = OUT2
Probe A - to red = GND
Probe B + to black = VR2-
Probe B - to yellow = VR2+

DIYAutotune seems to be changing their mind about what's going on with Digital Frequency In 3... Apparently they finally looked at the schematics... I suspect this is why it's seeing 8.x volts on the output, which is probably not a good thing. I'll stop using that input!

I double checked the schematics; it looks like Digital Frequency In 3 does have a 2.2K pull up to 12 volts on the MS3Pro Module itself. That may account for the different voltage peak to peak you're seeing. I'm less sure about the "bump" in the bottom of the square wave, but it may be a case of a small amount of voltage being injected into the ground plane at the bottom of the sine wave.

[jbelanger]

Your problem is that you're using VR+ and VR-. Neither of them is a ground or reference. You cannot connect the alligator clip to them or you'll screw up the signal on all the channels. Connect the probe to either VR+ or VR- and leave the clip unconnected. As long as you have the other clip connected to ground, you'll have a good reference point (ground) for all the channels.

That's the reason you were seeing the bump. You were moving the reference lower than 0V which made 0V look like it was moving up but it was only doing so with respect to the reference (the VR signal).

Jean

[rccardude04]

I suppose that makes sense. I was doing both since the VR sensor has two wires coming out of itself and no chassis ground anywhere. I figured it was just an alternating signal but didn't think about how it might affect the scope's ground. It makes sense that there would be some cross-talk though. I'll go out and try it with ground to VR+ or VR- and see if it makes anything happier. Maybe the reason my last Digital Frequency Input 2 scope reading looked good because I didn't have the alligator clip side of channel B actually making contact.

I appreciate the help!

-Eric

[jbelanger]

I suspected that this was your issue because that's not obvious when you're not used to working with a scope (or at least with that type of signal). You really need to think of the clip as the reference for all the signals and not simply the ground or the '-' of the signal you're measuring. You can get very confusing things if you just use it as the negative of the signal or use some unrelated ground or even forget to connect it (you'll get a lot of garbage this way: 60Hz from the mains or some other random interference (injectors, coils, motors,...). It's easy to forget about it even if you should know and you then waste time looking for the wrong thing (I've been there...).

[rccardude04]

To make sure I have this right: I should have the clips on the same ground wire (the power ground from the ECU in this case) and then scope VR+ or VR-, along with OUT2, yes? I can't just leave the second clip floating, but it needs to have a reference common to the output signal right?

I'll give that a shot within the next couple hours and see what it looks like. I'm going to assume whatever is actually causing my issues isn't happening right now then too, especially since everything works on both inputs. I have absolutely no idea what could have been causing it, especially since I've shortened/changed the wiring harness on both input and output now. I'd think if I had a connection issue it would have showed up, and I was careful with my solder joints. I guess one of the pre-assembled pins could have an issue. That's probably the next thing to look into just in case, otherwise I'll just wait for it to act up again.

Thanks!

-Eric

[jbelanger]

You can leave the clip floating as long as you have the other one connected to ground. They should all be connected together inside the device. This is also why you saw the interference between the signals. Connecting both clips to the same ground will also work but will be redundant.

Jean

[rccardude04]

Perfect, thanks! I'll see what happens.

[rccardude04]

That worked much better! Everything is acting how it should, so I still have an intermittent issue but I'll be leaving it on input 2 since there's no 12v pull-up there, and I also learned that I have an intermittent "ground" connection on one of my probes, which is probably why I saw a good signal on my last check - the ground probe for the VR wasn't actually connected.

Thank you for all the help!!!! Hopefully it's either fixed itself or acts up again where I can scope it and see what's actually going on.

A couple photos for posterity. Probably worth noting that the x10 switch was active on this wave:

Wave to DFI2 no pullup.jpg (898.01 KiB) Viewed 1063 times

Hooked up correctly, no pullup.jpg (793.6 KiB) Viewed 1064 times

-Eric