Sharing VR sensors

MalcolmV8 · Post by **MalcolmV8** » Thu Mar 02, 2017 11:00 pm

I'm installing a MS3Pro along side my factory ECU in a 2003 Cobra. The stock ECU will remain to drive the gauge cluster and other misc stuff it does, cooling fans etc. The MS3 however will drive the coils, injectors, and idle air control motor. This means both ECUs need to read crank and cam VR sensors. Is it OK to just splice into MS3 into the same wires two wires coming off the two VR sensors and let it feed both ECUs? If not how do I need to do it?

KAT PWR · Post by **KAT PWR** » Sat Mar 04, 2017 12:46 pm

I would think you need to build a op-amp circuit so you're not drawing on the signal need by the megasquirt ECU. but why run it like this? Megasquirt can control fans, what other stuff does it run besides the gauge cluster?

MalcolmV8 · Post by **MalcolmV8** » Sat Mar 04, 2017 1:10 pm

The gauge cluster is my main concern. Fans and what not are secondary and I can move to the MS3 at some point. I've not heard of having to do an op-amp circuit. You'd think the MS3 and the factory ECU have very high impedance inputs and don't actually put a drain on the VR circuits but I really don't know.

SwedCharger-67 · Post by **SwedCharger-67** » Sat Mar 04, 2017 1:19 pm

Without actually knowing I think you are right in assuming very high impedance inputs and most likely you can just splice the signal to feed both ECUs.

MalcolmV8 · Post by **MalcolmV8** » Sat Mar 04, 2017 1:32 pm

Yeah hopefully its that simple. Building a new motor so I'd like to fire it up on the stock ECU since I know fueling and timing will be correct and I can proceed to break it in. Once the motor's broke in and running decent I plan to start swapping over to the MS3 which I'm wiring in now. I'm using deutsch connectors to make the harness simple. Unplug ignition and injectors and IAC motor from stock ECU and plug into MS3. Fuel pump I'll probably swap over too. Most other stuff will be shared such as TPS, VR sensors etc. Coolant and intake air temps will be duplicated since I'm installing the GM sensors for the MS3 and I'll be adding a couple MAP sensors too. One for boost and one for barometric pressure.

I figured out the majority of it... I think lol. The VR inputs was concerning. We'll see how it goes.

KAT PWR · Post by **KAT PWR** » Sat Mar 04, 2017 1:51 pm

it might be that simple. I know with speed sensors (VR type) and most temp sensors you do you need a op-amp to buffer the cricuit as to not interfer with the main component using the sensor.

MalcolmV8 · Post by **MalcolmV8** » Sat Mar 04, 2017 2:08 pm

KAT PWR wrote:it might be that simple. I know with speed sensors (VR type) and most temp sensors you do you need a op-amp to buffer the cricuit as to not interfer with the main component using the sensor.

What sort of op-amp setup do you use? Be good info to know if I run into something like this.

KAT PWR · Post by **KAT PWR** » Sat Mar 04, 2017 9:20 pm

I've looked into it cause I wanted to data log oil temp and psi from one my gauges. When I tried tap into it the readings changed. I've looked into it, ordered the parts for the circuit, but I have yet to build and test it. All you need to do is build a simple Voltage Follower circuit
http://hyperphysics.phy-astr.gsu.edu/hb ... pvar2.html

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MalcolmV8 · Post by **MalcolmV8** » Sat Mar 04, 2017 11:43 pm

That's interesting because you'd think the MS3 has high impedance op-amp type inputs.

dontz125 · Post by **dontz125** » Sun Mar 05, 2017 6:59 am

The MS3 has the same VR inputs as the MS1 or MS2, because it's installed on the same mainboard, whether V3.0 or V3.57. The MS3-Pro has the newer MAX9926 input chips. What someone using a boxed MS3 *can* do is buy a Dual VR board from jbperf, which uses the same conditioning ICs, install it safely in the proto area & connect the output to the VR_out pad.

MalcolmV8 · Post by **MalcolmV8** » Sun Mar 05, 2017 7:25 am

dontz125 wrote:The MS3 has the same VR inputs as the MS1 or MS2, because it's installed on the same mainboard, whether V3.0 or V3.57. The MS3-Pro has the newer MAX9926 input chips. What someone using a boxed MS3 *can* do is buy a Dual VR board from jbperf, which uses the same conditioning ICs, install it safely in the proto area & connect the output to the VR_out pad.

Ah ok, I'm using an MS3-Pro. I have a bad habit of calling it an MS3 for short but realize that creates confusion with the actual MS3. I will make sure to be more clear on that. Thanks for clarifying those differences.

Manu · Post by **Manu** » Sun Mar 05, 2017 12:20 pm

Hi,

For this purpose I use to use a 1:1 transformator to split VR signal between ECUs.

MalcolmV8 · Post by **MalcolmV8** » Sun Mar 05, 2017 1:27 pm

Manu wrote:Hi,

For this purpose I use to use a 1:1 transformator to split VR signal between ECUs.

Can you share a link of such a transformer and how one would wire it up?

MalcolmV8 · Post by **MalcolmV8** » Thu Mar 09, 2017 7:44 pm

Well I decided to do some testing and figure this out. My engine is out the car and everything is tore apart so I had to get creative. So I built this little rig real quick to trigger the crank sensor.

Had it all rigged up on the ground like this and powered with the drill.

The stock ECU seemed to accept that input just fine. Even the tach was working on the dash. So I started the data logger on the stock ECU and verified everything looked nice. It did.
So then I wired in the MS3-Pro to the same circuit so it was sharing the crank VR sensor. First ran another test with the stock ECU and it responded good as before. Then I powered up the MS3-pro and once again the stock ECU had no issues. The data log on the MS3-pro look good too and they both data logged the same thing. Both show a peak RPM of 3191.

Here's the stock ECU data log

The ms3-pro

I also used the tooth logger diagnostic tool on the MS3-pro and the wave form coming in on the crank sensor looks good.

So unless I missed something I think I'm going to be OK with the MS3-pro and the stock ECU sharing VR sensors once my car goes back together. They appear to both be functioning as expected.

SwedCharger-67 · Post by **SwedCharger-67** » Fri Mar 10, 2017 12:38 am

Excellent work!

dontz125 · Post by **dontz125** » Fri Mar 10, 2017 6:56 am

Sure sounds like proof of concept!

MalcolmV8 · Post by **MalcolmV8** » Fri Mar 10, 2017 7:16 am

Yeah pretty happy about that working. It could have turned into a complicated mess.

Tjabo · Post by **Tjabo** » Sun Oct 22, 2017 11:57 am

Thank you for testing this and sharing the results! I'm setting something similar up right now with a VR sensor on a 60-2 wheel in a BMW, and I was worried I might not be able to share the crank sensor signal.

Flaming_Crossbow · Post by **Flaming_Crossbow** » Thu Jul 26, 2018 3:03 am

Manu wrote:Hi,

For this purpose I use to use a 1:1 transformator to split VR signal between ECUs.

Manu, are you willing to share what type transformator you exactly used?

DaveEFI · Post by **DaveEFI** » Thu Jul 26, 2018 3:16 am

MalcolmV8 wrote:That's interesting because you'd think the MS3 has high impedance op-amp type inputs.

I'd say the danger is the shared ground causing a ground loop and noise. Not loading down the VR sensor.

Pretty common problem with audio, so the cures are the same.

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