How to choose proper grounds for sensitive electornics (vehicle project) - Page 1
Forum section: electronics / projects

author: Mile Tzali
author_rank: Newbie
timestamp: January 13, 2022, 07:07:09 pm
content: Big noob alert! I'm tinkering with the good ole garage project, the standard stuff - 12V lead acid battery, stator, rectifier. I would like to put few additions to the circuit, you can see what I'm generally trying to do by my hastily done schematic.It uses couple of Arduino boards because each have a pretty critical function and Ardu Nano aren't great at multitasking so to avoid any issues I'll be using few of those, don't mind it.I am reading a lot lately on transients and noises in vehicle environment - load dumps, over and undervoltages, spikes, basically from what I can understand there's a lot of challenges to be tackled when tapping into vehicle power network and I want to make this proper. However, there's an OEM computer in the vehicle already, controlling the ignition, injection and the usual stuff, so there has to be some protection on that computer in order not to get fried by the various effects of cranking and such, correct?On the diagram you'll see most of the stuff isn't grounded. That's because I'm not sure where. Should everything be grounded to a single chassis ground bus? If Arduino is operating at 5V and battery is at 14V when running, is it safe to hook the Arduino to that same chassis ground? And what about the Arduino buttons, they will be used for logic level signals which is pretty crucial and needs to be exact. Should the buttons be grounded to Arduino GND or could they be grounded to chassis, since they will be physically "far away" from the Arduino.And also, another issue, bringing 12V to clean 5V, where do I look? I'm aware on Mouser they have various brands of isolated DC DC converters, however the more I read online the more it seems that none (or very few) of those converters are suitable for battery operated circuits, because of crank voltage drops for example, when voltage drops to 4V. If I understand it correctly, turning the key powers everything up since the fusebox gets powered via battery, all the converters start working because they usually have 9-36V range, and then when I crank, it drops under 9V shutting everything off, only to be turned on again due to engine turning over.So this means I need buck boost converter? Or does my circuit already have one somewhere? As far as I can read the schematic, I don't see any reference to such device. Sorry for the blogpostthanks for any help

author: m3vuv
author_rank: Super Contributor
timestamp: January 13, 2022, 11:15:11 pm
content: Hi,if it was me i would ground them all to the battery-ve,also run a few decoupling caps between +and ground to help with noise and spikes.think you would get issues jump starting etc tho,in the past a friend of mine set the airbags off on a mk3 vauxhall cavaliar by sticking a start charger on it,boss wasnt very happy!,was about a grands worth of damage at the time!.was about 1997

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: January 15, 2022, 12:57:37 am
content: Protection for OEM electronics equipment is built in to the unit not the vehicle. Overvoltage, reverse voltage, filtering and even overcurrent. These should be part of your design to start. ONE ground not many to start if you see problems then try adding ground/s.Jeff