MS2 - VR Input for tach signal

[krisr]

Hey guys,

I'm going to have another crack at setting up MS2 to take my tach signal from an MSD probillet distributor's VR sensor and have been doing alot of reading about the polarity of the MSD sensor & the polarity of how Megasquirt wants the signal. Apparently the probillet distributors send a neg-to-pos signal if the orange wire is +.

On this page http://www.megasquirt.info/ms2/vradjust.htm it says that Megasquirt takes a neg-to-pos input but inverts it to pos-to-neg. Would that mean that Megasquirt is triggering off the 'falling edge'?

Also going to try and use the VB921 to trigger an MSD6AL so would these settings in Megatune be the goods...

Input Capture: Falling Edge
Cranking Trigger: Trigger Rise
Coil: Standard coil charge
Spark Output: Going Low
Max Spark: 25.5
Max Dwell: 25.5

Has anyone else tried using a probillet distributor as their tach signal yet?

Cheers
Kris

[FoundSoul]

I have a customer in Missouri that I believe is running the MSD Pro-billet dizzy on a beast of a car-- he wasn't initially controlling it with the 'squirt (was just doing mech. adv.) but Dieselgeek recently made a trip out to his shop and he is now. Let me see if I can draw his attention here and maybe he can help...

[Bernard Fife]

On this page http://www.megasquirt.info/ms2/vradjust.htm it says that Megasquirt takes a neg-to-pos input but inverts it to pos-to-neg. Would that mean that Megasquirt is triggering off the 'falling edge'?

krisr,

Yes, that is correct. And since the optoisplator is not in the VR input ciurcuit, 'falling edge' is what you specify for 'Ignition Input Capture' in MegaTune.

(If you were triggering on the falling edge of an external square-wave trigger signal with the Hall circuit, HEI for example, the oprtisolator would invert the signal, and you would specify 'rising edge' in MegaTune.)

Lance.

[dieselgeek]

See my reply on the other post about this distributor. FOr other reasons on the car we had to revert back to fuel only, but we did test and run it with your config and we found it only worked feeding the MSD's "negative" wire (purple?) to the tach input on MS, and ground the other wire. Post up a datalog of your car idling, I always noticed a goofy "sine wave" in the RPM data if we had this backwards, and I've seen it on two other occasions using VR sensors as tach input: once on a rotary, and another time on an EDIS trigger wheel.

-scott

[bleoh]

Is an MSD distributer different then others with a VR sensor? On this page it has Spark Output going high and much lower dwell recommendations. (hope the link works) http://www.megasquirt.info/ms2/vb921.htm

Just trying to relate this to my setup and issues I'm trying to work out.

Brian.

[dieselgeek]

Is an MSD distributer different then others with a VR sensor? On this page it has Spark Output going high and much lower dwell recommendations. (hope the link works) http://www.megasquirt.info/ms2/vb921.htm

Just trying to relate this to my setup and issues I'm trying to work out.

Brian.

and I totally forgot to mention the installs above were with MS-1, but the v3 PCB using it's onboard VR conditioner circuit. I am reading that the MS-II gives you different options for triggering - so my suggestions above might be useless.

let us know how you get it to work,
-scott

[krisr]

Thanks Guys! I can feel the love

I'm fairly confident that i'll get it running now I have more of a grip how the trigger offset and rotor phasing works in relation to MS2. That is where the original problem stemmed from 6 months ago I think. Like when cranking it would fire about 50-60°BTDC and when I did manage to get it to fire, it would have a bad miss everywhere and backfire out the exhaust like it's well to retarded.

Anyhow I have to modify the plenum chamber this weekend and put some vacuum fittings in the back then make a test harness to try get this thing running! Shall report back.

Cheers
Kris

Ps. Thanks for your help Jerry! Much appreciated!!

[busta9876]

i just finished my MS II v3 main board tonight, everything tests out. i am initially installing this on a TPI 305 and MSD 6AL box, Pro Billit Dizzy,

after i work out bugs and get that running, 496 stroker BBC

[krisr]

I have just scoped my Pro Billet distributor and indeed i'll have to invert the wires because if the orange wire is (+), it will transmit a pos-to-neg signal....

So yeah, invert your probillet pickup coil wires and you should be fine..

I did manage to get mine running even though the wires were backwards but with the twist of the distributor it triggered at idle fine.

[busta9876]

I have just scoped my Pro Billet distributor and indeed i'll have to invert the wires because if the orange wire is (+), it will transmit a pos-to-neg signal....

So yeah, invert your probillet pickup coil wires and you should be fine..

I did manage to get mine running even though the wires were backwards but with the twist of the distributor it triggered at idle fine.

How did the R52, R56 pots have to be adjusted on your probillit?

I set both of my pots at full counter clockways rotation. I can pick up rpm as low as 70 rpm . I have the harness laying in the floow and a Makita drill taped to pro billit dizzy. I can get rpm from 70rpm up to 1700, max my drill goes.

I noticed as I increased ether POT it wouldn't read as low rpm.
The instruction said R52 all ways counter clockways, R56 all wasy clockways..this didn't work for me.

Do i want to be able to trigger MS at 70 rpm? or should it be higher?