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Topic: 3.3V regulated Arduino Pro mini Communicate 5V SERIAL ???? (Read 1 time) previous topic - next topic

boraciner

Hi everyone..
I connected a arduino pro mini 3.3V with Ericsson T290i , Uc is talking with mobile perfectly. I have a GPS module which runs at 5V then Can I connect rx and tx pins of GPS to 3.3V regulated Arduino ?
Can it communicate with GPS ??
thanks ..

GPS : Skylab SKM53

winner10920

You could get a level shifting ic which would be the best way
or use a voltage divder on the arduino rx, and nothin on the tx it should work

boraciner

I just need TX of GPS .. Can I connect it directly ??

winner10920

No, tx of arduino is safe for gps but gps tx isn't safe for the arduino rx
You need either a voltage divider or a level translator

boraciner

I connected it directly.. It works for 15 mins ;) hope that It'll be ok! =)

winner10920

Well yes it is working, and Im not sure the exact implications but if you want it to continue working as expected its better to do it the right way
There's usually a reason that the datasheet says the max voltage on any pin is vcc
I had a nrf24l01 wireless module that I didn't realize was 3.3v, it had 5v tolerant inputs but was powered 3.3, I supplied 5v and it worked great for two uses of about 10 min
the second time I realizdd it was kinda hot,
there was no third time it worked...

boraciner

now 3 hours has gone .. and its working ,,,, excellent !!! =)

winner10920

Hmm, never actually tried something like that before
technically the atmega328 has a max vcc of 5.5v, but max input of vcc + .3 or something like that
Post back if anything goes wrong, perhaps this is one spec that isn't so damaging since it can be 5v powered anyway

boraciner


MarkT


now 3 hours has gone .. and its working ,,,, excellent !!! =)


You definitely risk destroying the Arduino or the GPS (or both) - its not worth it.  You probably have already compromised the performance of the Arduino pin by overheating its protection diode and nearby transistors.  You may also be powering the Arduino's 3V3 rail through that diode and raising it to more like 4V.  Feeding excess current into a protection diode can also trigger a phenomenon known as "SCR latchup" - when this happens the whole chip will start conducting heavily and heat up rapidly and burn out.

The simplest fix is to place a 10k resistor in line with the GPS-TX to Arduino-RX connection.  This limits the protection-diode current to about 150uA which it should be able to handle without cooking or risking latch-up.

If you are lucky the GPS outputs are already current-limited and this explains why things still work - but this is a bad and expensive habit to get into - datasheets have a section at the top called "Absolute Maximum Ratings" - exceed these and all bets are off.
[ I won't respond to messages, use the forum please ]

boraciner



now 3 hours has gone .. and its working ,,,, excellent !!! =)


You definitely risk destroying the Arduino or the GPS (or both) - its not worth it.  You probably have already compromised the performance of the Arduino pin by overheating its protection diode and nearby transistors.  You may also be powering the Arduino's 3V3 rail through that diode and raising it to more like 4V.  Feeding excess current into a protection diode can also trigger a phenomenon known as "SCR latchup" - when this happens the whole chip will start conducting heavily and heat up rapidly and burn out.

The simplest fix is to place a 10k resistor in line with the GPS-TX to Arduino-RX connection.  This limits the protection-diode current to about 150uA which it should be able to handle without cooking or risking latch-up.

If you are lucky the GPS outputs are already current-limited and this explains why things still work - but this is a bad and expensive habit to get into - datasheets have a section at the top called "Absolute Maximum Ratings" - exceed these and all bets are off.


Thanks for your message, I'll connect a resistor if I connect another 5V serial device ;)

winner10920

Well isn't the protection zener 5.1v or something like that? The atmega328 is a 5v device, that one is just running at 3.3 v so is there a problem with this setup? Or does it actually work safely?

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