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I have a device called AutoPi (https://www.autopi.io) which is simply a Raspberry Pi Zero aggregated with a couple of more components.

The device takes it's power from the OBD port.

I want to make a simple intermediate circuit between the OBD port and the device to power the device from an external battery (possibly a power bank) instead of the OBD port.

Here is a brief diagram of what I plan to do :

case 1

Questions about this is :

Would this circuit possibly cause damage to the device or the car computers ?

I guess that it is unlikely but is there any possibility to introduce noise or cross talk to the data lines, how would one prevent it?

I would also like improve it by adding a switch to disconnect the data lines from the device on demand.

In this case should I leave the data lines floating or should I connect them to ground ?

About the grounds, should I connect my device to the signal or chasis ground or both ?

Thank you for your support.

Ali Somay
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  • I now found out about this question which is very similar to mine https://electronics.stackexchange.com/questions/281715/connecting-usb-powered-beaglebone-to-cars-can-bus-through-obd-connector-using-c?rq=1 but I would still love to receive an answer :) – Ali Somay Feb 19 '20 at 20:17
  • This one also answers a part of question, I guess I should have researched more. https://electronics.stackexchange.com/questions/239970/should-i-tie-signal-gnd-pin-5-and-chassis-gnd-pin-4-together-on-obd-ii-port?rq=1 – Ali Somay Feb 19 '20 at 20:30
  • Putting a switch to the data lines part still waits for an answer though – Ali Somay Feb 19 '20 at 20:31
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    If you power it externally, why would that damage the car electronics? The EMC concern might be valid, Rasp PI is a _toy computer_, so why are you using it in a professional application? Car electronics are rugged and able to withstand noise, toy computers are not. Your concern should be if the car introduces noise that disturbs the toy, rather than the other way around. – Lundin Feb 20 '20 at 09:40
  • I built the prototype of the circuit today, and it worked pretty well btw. I just wanted to ask because I am not a full fledged electronic engineer myself and maybe thought there might be some dangers which I might not foreseen yet n this setup. I tried the switch also, do you think it would be necessary to route the data lines to GND when the connection is cut ? – Ali Somay Feb 20 '20 at 15:44

1 Answers1

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I have built the device and it is working perfectly fine, there are no issues at all.

I have also added a buffer with a capacitor (10000 uF) so I could switch between the car battery and external battery seamlessly with a DPDT switch, this also works very fine.

I didn't experience any significant inrush current in my configuration.

Thank you very much for your comments.

Ali Somay
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