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Topic: rs-232 wire gets warm (Read 992 times) previous topic - next topic

jerseyguy1996

I have noticed that if I run my freeduino (NKC Electronics Serial V.1)  from a 9V wall wart everything is fine but if I run 9 volts (voltmeter shows 8.71V) from a computer power supply through the Vin and Gnd, the rs232 line gets noticeably warm.  Is there a current limiting resistor that I should be running in between the power supply and the Vin on the board?  Looking at the schematic for this board, it seems that the input from the wall wart and the Vin are electrically common except for a 1N4004 diode that runs between them.  Any ideas on why this may be happening?

Arduino Uno;
Mega328

nkcelectronics

What do you mean by Computer Power Supply?  I don't remember seeing 9V coming out of a PC power supply, only 12V and 5V.

Grumpy_Mike

It's almost certain it is an earth problem. Try disconnecting pin 5 from X1.

jerseyguy1996

Oh geez I bet you are right.  I didn't even think of that.  I am getting the nine volts from the power supply by using the +12V and +3.3V wires.  The rs-232 is expecting a true ground and my 9V is referenced to a +3.3V ground.  I'm surprised I didn't fry my serial port or worse my entire mother board.  I'm really new to this hobby so unfortunately I will probably make many more of these mistakes.
Arduino Uno;
Mega328

follower

Quote
I am getting the nine volts from the power supply by using the +12V and +3.3V wires.

I seem to recall reading somewhere that it was unwise to do that.

--Phil.

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