I have an Arduino Nano Every with a small, or maybe not so small, problem. The voltage on the SDA line is about 6.3 volts when I power the Arduino using Vin, with 9V. Sometimes it is even higher, nearly Vin voltage. This is causing my I2C multiplexer to backfeed the 5V bus with this higher voltage. Obviously, this is not an acceptable situation. Is my Arduino toast?
It sounds like the regulator on the Nano Every is bad, or there is a bad part or connection somewhere on the PCB.
If the Every still seems to work, it probably won't for long and is not safe to use with anything else. Replace the Every.
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- Tell us how you are measuring these voltages ?
Hi, @vpeppers
Can you post some images of your project?
So we cab see your component layout?
Can you please post a copy of your circuit, a picture of a hand drawn circuit in jpg, png?
Hand drawn and photographed is perfectly acceptable.
Please include ALL hardware, power supplies, component names and pin labels.
Thanks... Tom.... 
Digital VOM. I kept reading Vin levels on my 5V bus and started pulling wires until it went away. That wire was the SDA pin, so I measured that.
It’s rather complicated, and still in breadboard stage. Wires are everywhere, and you wouldn’t see much.
Hi,
A schematic would help.
Tom....
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Well let us see.
Disconnect everything, upload the blink example sketch and see if it works.
What do you mean, it went away.
Vin on the 5V means you had a short from Vin to 5V.
Tom....
With nothing connected to the Every but 9V to the VIN pin and GND, you should have 5V on the 5V pin. Did you measure that?
I’ll see what I can come up with.
I mean that I had Vin on my 5V bus, until I pulled the wire from SDA. Then the 5V bus dropped to the expected 5V.
Good thought. I’ll try that tonight.
Did the blink work?
If the board is fried it won't matter what voltage you read.
I missed that you had an I2C multiplexer. What type multiplexer, and how is it wired? The complete schematic, as requested by @TomGeorge, would definitely help.
Can the unexpected voltage be coming through the I2C pullup resistors of a connected peripheral ?
Hi, @vpeppers
Are you using external pullup resistors on the I2C bus, if so what value?
Thanks... Tom....
Does this translate to:
"I have incorrectly powered some I2C device at vin voltage instead of 5V and this device has onboard pull-ups on supply voltage"?
No. What has happened is that when I put Vin (9v) onto the Arduino, the voltage on the SDA line jumps up to Vin. The SDA is not even currently connected to my multiplexor. Sorry for the confusion. I have been extremely busy, and have not been able to create the circuit diagram that is needed. I will try to do that as a benefit to others.
Thanks so much to all of you guys for your many helpful tips. You have given me several thoughts about testing the Every. However, I have concluded that the device is bad, and I have ordered a new one. If it does the same thing, I will be back with the circuit diagram, etc, and we will pursue this. I really think that the new device will solve my problem. I think I have fried it someway. It won’t be my first, and probably won’t be the last. I am a mechanical engineer, not an electronics expert, and a lot of this is over my head. It just works magically for me. I am looking forward to the new chip, and to see if it fixes my problem. If so, hopefully my electronic speedometer will be working. If so, I will post a picture, and a full circuit diagram, along with the code, for others to use. I’m sure you guys will have fun poking holes in my programming!