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I'm tinkering on my garage project, standard vehicle stuff - 12 V lead acid battery, 3-phase stator, reg/rec. I would like to put few additions to its circuit. Being a rookie, I'm not sure how to approach this correctly in terms of providing safe 5 V for the Arduinos (I need few of them). I've read a lot of articles on transients and noises in vehicle environment - load dumps, over and undervoltages, spikes...and also proper grounding, ground loops, it just seems overwhelming - hence this thread.

I've sketched up (sorry for any drawing mistakes) the circuit I plan to make, there's two of the sketches actually - the difference being grounding of the Arduinos, since I don't know which method is actually correct, grounding them to chassis or grounding them to the buck converter that will be providing the 5 V. I have a Traco Power TMDC 20 unit for this job - if you have the time you can look up its specs, from my limited knowledge that converter should be good for my use case but do let me know if its not.

enter image description here

Also another issue I'm worried about is grounding Arduino's buttons for logic level signals - I presume they all should be grounded on the Arduino GND pin - but then there's a issue of physical distance. The buttons themselves will be at least 2 meters away from the Arduino, if not more - so this makes me think about interferences, noises on the wire, etc. - how do I approach that issue? Here's the schematic and thanks for any help.

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    \$\begingroup\$ You need to make a rough calculation regarding current consumption and then see if the power supply is sufficient. As for if some generic Traco module can handle surges and noise... probably not, or I wouldn't count on it. I would place an 18V-20V something TVS before the Traco. \$\endgroup\$
    – Lundin
    Jan 14 at 13:02
  • \$\begingroup\$ The 5V rail shouldn't draw too much - Arduino 1 will only need whatever minimal current for the logic levels on the pins, Arduino 2 sensor draws 100mA max (spec sheet) and the LED driver powers approx 30 small (3535) LEDs, around 1A if full brightness is used (which it wont). So to be safe and have plenty of margin, the 5V rail will need to provide 2A, even though realistically it will probably use 1A but just in case and for possible future proofing. I'll look around YouTube to get some basics on how TVS diodes work and which should I choose for my application, thanks! \$\endgroup\$
    – Varonne
    Jan 14 at 13:12
  • \$\begingroup\$ My experience of Traco modules is that they will lie down to die if you exceed their specified current limit with 1mA or so. So make sure you have margins. \$\endgroup\$
    – Lundin
    Jan 14 at 13:20
  • \$\begingroup\$ Anyway, an answer depends on if you just want some little hobbyist project mounted on some vehicle that will never be used in traffic, or if you are designing a professional automotive qual product. Because you would never be using Arduino in the latter case. And in the former case, you would just patch something together without too much concern. \$\endgroup\$
    – Lundin
    Jan 14 at 13:41
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I have little doubt in recommending the first circuit (redrawn slightly to fit the page better and with extra added information): -

enter image description here

The object of this exercise is to keep the fragile and sensitive Arduinos away from the chassis ground connection. This means opto-isolated inputs for all ground referenced sensors.

grounding Arduino's buttons for logic level signals - I presume they all should be grounded on the Arduino GND pin - but then there's a issue of physical distance. The buttons themselves will be at least 2 meters away from the Arduino, if not more - so this makes me think about interferences, noises on the wire, etc - how do I approach that issue?

I'd use opto-isolation as shown above. Let the opto device take the strain and not the Arduino.

I have a Traco Power TMDC 20 unit for this job

This device is just not going to withstand some of the big surges seen in automotive applications without added surge protection devices. The 24 volt module (suitable for 12 volt batteries) is maxed at 50 volts peak and this is just too low IMHO.

You also need to fuse the power feed to the Traco to prevent fires should it go faulty but, if you insert this circuit based around the LTC3895 it will suppress surges up to 140 volts and provide current limiting: -

enter image description here

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  • \$\begingroup\$ What is missing is the implied GND connection between Arduino1 and the high side switch shield. Despite at least three questions, the OP has not stated exactly what this shield is. My guess is the Infineon one, which is not isolated. \$\endgroup\$
    – Kartman
    Jan 14 at 16:26
  • \$\begingroup\$ Well, as always, we are reliant on the OP providing decent information on which to make decent recommendations. \$\endgroup\$
    – Andy aka
    Jan 14 at 16:32
  • \$\begingroup\$ @Andyaka the high side switch shield I'm using is [eu.mouser.com/ProductDetail/Infineon-Technologies/… here on Mouser) and from what I can see it has protection, I also tested it on my work bench with bench PSU, using 5V on Arduino 5V pin and bench PSU to the shield, all the way to around 30V (for a moment) and all worked fine. \$\endgroup\$
    – Varonne
    Jan 14 at 20:36
  • \$\begingroup\$ Where is it in your block diagram. It’s meaningless mentioning it unless it’s clear where it’s used. \$\endgroup\$
    – Andy aka
    Jan 14 at 21:35
  • \$\begingroup\$ @Varonne the block diagram for that driver board explicily shows no isolation and that the gnd for the 12V side is the same on the Arduino side. It's not that it won't work, but that you are hanging your hat on an expensive isolated converter that isn't of much benefit to you. I said the same at least four times now and you keep asking the same question. You want an automotive rated buck converter - non isolated. Your system gnd is the point where it enters your board - on the Infineon shield. \$\endgroup\$
    – Kartman
    Jan 14 at 22:48

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