Hello,
my car uses VR sensors for engine positioning.
The wiring example connects the second pin of the VR sensor to digital ground. But a VR sensor is a analog sensor, not a digital one like a hall sensor. So is this really correct in the manual?
(An answer from ecumaster staff would be great.)
thx
Bastian
Hi
i am not ECUmaster stuff but this is a general ECU design topic.
It is not about if the sensor outputs an analog or digital value but how it is read. If u expect/configured a digital result of the sensor then connect it to digital ground. Crank sensor independend of Hall or VR always results in a digital results.
A ciruit is either desinged for digital or analog results/measurements depending on the usage.
Each then has specific pro and cons.
Crank sensor needs fast edge detection and high frequency measurement. So it is better and faster to directly detect the edges on HW side with specific circuit desings for that usage.
U can also analyse a hall sensor with an analog input and it will work till a specific point.
In the end the seperate digital ground is existing to protect the analog sensors from effects of the digital measurement circuit. Digital stuff is always more likely to creat noice on the ground side.
Just did 10k rpm plus dyno pulls on a mag sensor using A20 as the ground. Zero issues. Same for some 4cyl mag trigger that was spinning to 8700, no issues. Shield and drain proper, you should be good.
If u connect ur high frequency digital sensor to analog ground u dont creat an issue with that sensor. If this sensor is working it is no prove that all is good.
If u connect it like that then it is possible, that u are throwing some noice an the analog ground, which may impact the reading of real analog sensors connected to that ground. So in that szenario u should better watch the readings of the analog sensors.
Hi,
Yes, the manual is correct.
If we go back to fundamentals, every voltage signal is analog. Doesn’t matter if the voltage is like a square wave. It is still a continuous signal that can take any voltage within the operating range (i.e., 0-5 V). The distinction between “digital” and “analog” signals is created by humans for easier communication. This distinction is irrelevant in physics.
So what decides which ground path to use?
The current flow.
People seem to forget that every electric circuit has a current flow in a closed loop. That includes the circuit created by the sensor and ECU. We can treat the sensor like a small battery whose voltage changes depending on certain factors. For the ECU to measure the battery (sensor) voltage, we need an electric circuit. The current has to flow from this battery to the ECU, go out of the ECU, and back to the battery to complete the loop.
The final point is that to minimize the effects of external noise on the circuit, the current loop must have the smallest possible area. In practice, that means the current flowing from the source and the current returning to the source should be physically close together.
The digital input circuit in the ECU is connected to the digital ground. That means the easiest and shortest path for the current entering the digital input is through the digital ground and back to the source. The same goes for analog inputs and analog ground.
TLDR:
Which ground you have to use depends on the input type, not the signal/sensor type.
Digital inputs are paired with digital ground.
Analog inputs are paired with analog ground.
Power outputs are paired with a power ground.
