How critical is ground distribution?

[ViperSpecialty]

On the car I am working with now, there are a total of 11 sensor grounds:

Pedal 1
Pedal 2
TPS 1
TPS 2
Bank 1 Sensors {ECT, MAP 1, EOP, NTK1} +Crank
Bank 2 Sensors {EOT, MAP 2, FP, NTK2} +Cam
Cal Pot
Trac Pot
MAF 1 [12V Ang]
MAF 2 [12V Ang]
Wheel Speed [12V Dig]

I had planned on running Power/Ground like this with an SQ6M12:

Power 1: Pedal 1/TPS1/Bank1 +Crank
Power 2: Pedal 2/TPS2/Bank2 +Cam
Power 3:
Power 4: 12V Wheel Speed/PWM

ANG G1: Pedal 1/TPS1/Bank1/Cal Pot
ANG G2: Pedal 2/TPS2/Bank2/Trac Pot
Crank/Cam G: Crank & Cam
Dig G1: Dual Knock Sensor Ground
Dig G2: Wheel Speed/PWM SS Relay [5ma draw max @ 12V]
Comms G: MAF 1/MAF 2


Anyone have any suggestions on things that should be paired, separate, etc?

Also, Does anyone know if the actual internal function of grounds on the SQ6M12 are really different, or if they are just labeled as "analog" and "digital" for the sake of the end user?

[Neel]

Frankly, they are all connected in the ECU with filters to isolate noise from one another.

Power 1: Pedal 1/TPS1/Bank1 +Crank
Power 2: Pedal 2/TPS2/Bank2 +Cam
Power 3:
Power 4: 12V Wheel Speed/PWM

ANG G1: Pedal 1/TPS1/Bank1/Cal Pot
ANG G2: Pedal 2/TPS2/Bank2/Trac Pot
Crank/Cam G: Crank & Cam
Dig G1: Dual Knock Sensor Ground
Dig G2: Wheel Speed/PWM SS Relay [5ma draw max @ 12V]
Comms G: MAF 1/MAF 2

What do you mean nby Power 1-4? Which pins/outputs are your referring to?

The rest of them make sense. Except I would not run a relay off of Dig G2. All relays go to chassis ground. They can be noise inducing and don't need anything else. Also, use Comms ground for RS232 & CAN ground ONLY.

-Neel

[ViperSpecialty]

Frankly, they are all connected in the ECU with filters to isolate noise from one another.

Power 1: Pedal 1/TPS1/Bank1 +Crank
Power 2: Pedal 2/TPS2/Bank2 +Cam
Power 3:
Power 4: 12V Wheel Speed/PWM

ANG G1: Pedal 1/TPS1/Bank1/Cal Pot
ANG G2: Pedal 2/TPS2/Bank2/Trac Pot
Crank/Cam G: Crank & Cam
Dig G1: Dual Knock Sensor Ground
Dig G2: Wheel Speed/PWM SS Relay [5ma draw max @ 12V]
Comms G: MAF 1/MAF 2

What do you mean nby Power 1-4? Which pins/outputs are your referring to?

The rest of them make sense. Except I would not run a relay off of Dig G2. All relays go to chassis ground. They can be noise inducing and don't need anything else. Also, use Comms ground for RS232 & CAN ground ONLY.

-Neel

Power 1-4 = Pins 33, 55, 15, and 16... in that respective order. Keep in mind this is for the SQ6M12, not the SQ6.

Understood on the Relay, but it is not exactly what you are thinking. It is a Solid State PWM switching relay that is capable of up to 15KHz, and is PWM Low-Side activated. The "control" is basically more or less the legs of a high speed power transistor, not an actual relay. If you haven't ever worked with one of these, let me know, I probably have a couple more around here. They are FANTASTIC for building a PWM Fuel Pump controller that ramps up pump speed based on whatever control table you decide to set up. Works very well to keep from overheating fuel on return type systems, and keeps noise way down on street cars with gigantic pumps. I use it to control my Weldon D2345, and it doesn't even break a sweat in doing so, as they are rated at 75 amps continuous. You can also use them as a more reliable alternative to standard relays... no contacts to ever wear out. Another application could be a continuously variable fan speed controller.

Also, with regard to Comms Ground, is that the ground I should be running with the Omega dash, since it does use both Serial and CAN connections?

Lastly, where would be the best place to ground the MAF sensors? I hesitate to ground them with any of the 5V sensors since they are 12V sensors.

[Neel]

Understood on the Relay, but it is not exactly what you are thinking. It is a Solid State PWM switching relay that is capable of up to 15KHz, and is PWM Low-Side activated. The "control" is basically more or less the legs of a high speed power transistor, not an actual relay. If you haven't ever worked with one of these, let me know, I probably have a couple more around here. They are FANTASTIC for building a PWM Fuel Pump controller that ramps up pump speed based on whatever control table you decide to set up. Works very well to keep from overheating fuel on return type systems, and keeps noise way down on street cars with gigantic pumps. I use it to control my Weldon D2345, and it doesn't even break a sweat in doing so, as they are rated at 75 amps continuous. You can also use them as a more reliable alternative to standard relays... no contacts to ever wear out. Another application could be a continuously variable fan speed controller.

We're familiar with this system and Pectel has fuel pump control built-in that you can use. We use solid state relays all the time for fuel pump, nitrous and variable speed fan control. The Digital Grounds are MEASUREMENT grounds. They are there to provide a ground reference to a sensor. The relay, solid state or Otherwise is not a measurement item and actually sends a LOAD - in other words - current flows through this, however small, to ground. There is no benefit I can think of to grounding a relay to a protected ECU ground, but plenty of downsides in terms of noise introduced into the system. If your chassis ground isn't good enough to trigger any kind of relays, you have much bigger issues.

Same goes for the OMEGA dash. There is a current load going through its power to ground. This should go to the chassis ground.

The MAF is an odd case. Even though it does draw a tiny bit of current, the temp sensor built into it is an RTD, meaning you have to ground it with analog ground. To minimize noise issues, and since its very low current anyway, power it from what you call Power 3.

-Neel

[ViperSpecialty]

Understood on the Relay, but it is not exactly what you are thinking. It is a Solid State PWM switching relay that is capable of up to 15KHz, and is PWM Low-Side activated. The "control" is basically more or less the legs of a high speed power transistor, not an actual relay. If you haven't ever worked with one of these, let me know, I probably have a couple more around here. They are FANTASTIC for building a PWM Fuel Pump controller that ramps up pump speed based on whatever control table you decide to set up. Works very well to keep from overheating fuel on return type systems, and keeps noise way down on street cars with gigantic pumps. I use it to control my Weldon D2345, and it doesn't even break a sweat in doing so, as they are rated at 75 amps continuous. You can also use them as a more reliable alternative to standard relays... no contacts to ever wear out. Another application could be a continuously variable fan speed controller.

We're familiar with this system and Pectel has fuel pump control built-in that you can use. We use solid state relays all the time for fuel pump, nitrous and variable speed fan control. The Digital Grounds are MEASUREMENT grounds. They are there to provide a ground reference to a sensor. The relay, solid state or Otherwise is not a measurement item and actually sends a LOAD - in other words - current flows through this, however small, to ground. There is no benefit I can think of to grounding a relay to a protected ECU ground, but plenty of downsides in terms of noise introduced into the system. If your chassis ground isn't good enough to trigger any kind of relays, you have much bigger issues.

Same goes for the OMEGA dash. There is a current load going through its power to ground. This should go to the chassis ground.

The MAF is an odd case. Even though it does draw a tiny bit of current, the temp sensor built into it is an RTD, meaning you have to ground it with analog ground. To minimize noise issues, and since its very low current anyway, power it from what you call Power 3.

-Neel

Haha, you know, we were discussing a completely moot point with regard to the SS Relay- I just realized that I put the SS Relay onto that digital ground entirely by mistake in the first post... it doesn't NEED a normal ground in the first place. The SS Relay is PWM Low Side activated, the control wire *IS* its control ground. I just noticed it wasn't on my I/O list, and it clicked as to why I left it off. Whoops! Glad to hear you are using SS Relays however, they are pretty neat... but nobody seems to use them.

I understand what you mean with regard to measurement ground, but some of the cases dont seem so cut and dried. [such as the Omega, since it does use Serial/Can datastreams] Although, it makes much more sense when you look at it in terms of a "measurement" ground or not. I didnt think of it entirely that way.

The MAF is even more odd than you think, haha. The MAF's get power via the ASD system, there is no need to power them via a sensor power supply. However, since I will not be regularly using COMMS ground for anything, would it make sense to ground them there to isolate them from everything else? If I am reading over everything correctly, Comms ground is really only used for the Serial port, and that would really only be used for controller reprogramming, which would be a "key on, engine off" scenario anyway, meaning the MAF's would have no power as the ASD circuit is inactive.

[Neel]

You use the comms grounds for the shield wire on the RS232 wires going to the Omega dash. For shielding, you always only connect it on one side. For example, if a sensor has a shield pin, run the shield all the way to the ECU but do not terminate the shield to anything. For the Omega dash, you terminate the shield to the Comms ground, then run it all the way to the omega, where its capped off and not terminated.

[ViperSpecialty]

You use the comms grounds for the shield wire on the RS232 wires going to the Omega dash. For shielding, you always only connect it on one side. For example, if a sensor has a shield pin, run the shield all the way to the ECU but do not terminate the shield to anything. For the Omega dash, you terminate the shield to the Comms ground, then run it all the way to the omega, where its capped off and not terminated.

Should those two or three wires be twisted? Or, would it be preferable to use shielded wire for Serial, CAN, and Crank/Cam? I was already planning on using twisted pairs for Wheel Speed, and possibly twisting or shielding the Crank/Cam signals, perhaps do those as well...?

Would you anticipate any problem ground the MAF's to Analog 1 & 2 respectively?

[Neel]

You should use twisted, shielded wire in its own jacket for all comms, crank/cam and wheelspeeds.

You should ground the MAFs to an analog ground.