I am trying to use Arduino Uno, Seeed CAN Shield and Freematics OBDII adapter to make my own car gadget that reads car data and displays it on gauges and display, but I have encountered something that I want to clear out before proceeding. So the OBDII port has two grounds, chassis ground and signal ground. If I understand correctly, signal ground is from computer, is low noise and is used for CAN comms and stuff (in OBDII case), while chassis ground is for anything that requires reasonable amounts of power and is tied directly to car battery negative terminal. Also, the grounds are supposed to be tied together at some point by car manufacturer if everything is done properly. Here's the thing, I read around that its not recommended to tie them together by yourself (yourself = at OBDII port) because you can cause ground loops and introduce noise to signal ground, but many gadgets (Freematics OBDII adapter included) do this - I assume then that its the right thing to do, or is is a "cheap" way out that can cause problems? I'm a bit puzzled, is it okay to proceed this way? I don't want to cause car problems with my gadget. Any insights are appreciated, thanks!
Likely the connection between signal ground and battery ground exist in the car.
Make a wiring diagram for Your project and know were the controller gets its ground from.
I don't believe in a any serious issues, only poor functioning, unreluable data etc. if there is a ground loop or not.
Railroader:
Likely the connection between signal ground and battery ground exist in the car.
Make a wiring diagram for Your project and know were the controller gets its ground from.
I don't believe in a any serious issues, only poor functioning, unreluable data etc. if there is a ground loop or not.
Thanks for reply! So with a multimeter I have measured the signal and chassis ground pins of Freematics Adapter and they surely are tied together, so Arduino and Seeed Shield are tied to both grounds directly. The device that Seeed Shield will communicate with needs to share same ground as Arduino due to CAN comms, but at the same time I dare not connect it exclusively to signal ground because it could overload it (not sure how much old instrument clusters draw - that's what I will send data to from Arduino, an old cluster). Even if I wanted to separate I would need to ditch Freematics adapter because it ties them together inside. So if there is no possibility of confusing car computer with it I will proceed, thanks
This is sometimes a problem using mains powered measuring devices. There are occasions when the protective ground needs to be disconnected. Then we are at a high university level....
If You can use either a totally separate power supply, or a 12 volt converter being galvanicaly separated from the car ground You will have choices....
