Will I fry my 3.3V RX/TX pins when reading directly from an OBD-II UART?

Other Miscellaneous
1

Hello Gurus,

I’m happily reading data from my SparkFun OBD-II UART to a SparkFun Artemis RedBoard ATP. In my online searches however, I found[ this post[/b] that recommends connecting a logic level converter so not to fry 3.3V pins.
Is this actually the case though? I’ve been reading data for a while directly without issue (perhaps not for long after a puff of smoke?). Looking at [the schematics, I’m not seeing anything conclusive.
So far I did try wiring up my own logic level converter [based on a schematic (from OBD-II TX to ATP RX/GND). This resulted in no messages being received…
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wiring.png**
I could fork out the $3.00 + shipping [for this. That’s not all that bad, however my significant others’ eyes are burning through the back of my head as I make repeated small purchases for a project lol! I just want to check first before making a purchase.
Thanks for taking a look.](https://www.sparkfun.com/products/12009)](How to Level Shift 5V to 3.3V | Random Nerd Tutorials)](https://www.sparkfun.com/datasheets/Widgets/OBD-II-UART-v13.pdf)](IoT4Car - Hackster.io)

2

Hi veyor.

You definitely do not want to apply 5 volts to any pin on the Artemis RedBoard as those are not 5 volt tolerant. The OBD-II UART does have a 5 volt serial interface on it so you need some sort of logic level converter.

If the resistor divider you’re using now is working, it’s probably OK to stick with it. I’d swap that 1K resistor for a 1.2K though if you happen to have one just to make sure you’re under 3.3 volts on that RX pin.

If you find that data is being corrupted when you transfer larger amounts of data or at higher speeds, you would then want to change to the bi-directional logic level converter. It’s a handy and inexpensive part to have and you might want to toss one on your next order, but I can understand it being cost prohibitive to order just that one item. :slight_smile:

3

Cool. Thanks for the feedback TS-Chris. I went ahead and purchased a logic level converter. I want my board to last! :smiley:

Kind regards,

Chris