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Topic: Proper way to provide a ground output from arduino UNO (Read 911 times) previous topic - next topic

michinyon

This is a good question.   I have a similar question.

I am supplying an arduino with an 8V power supply through the concentric plug.  Is it OK,  to have the ground pin of the arduino connected to the negative side of this power supply ?

JimboZA



I am supplying an arduino with an 8V power supply through the concentric plug.  Is it OK,  to have the ground pin of the arduino connected to the negative side of this power supply ?


I thought the neg of the plug was the ground?
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johnwasser


I don't mean to be a pain with this, but if anyone can help I would greatly appreciate it.


You say you are trying to 'ground' an input to the ECU that has a 5V pull-up.  You say you need "zero resistance to ground" but that makes no sense in a digital logic circuit.  If the ECU uses 5V logic it should be sufficient to get the pin down to, say, 0.25V to ensure it is read as LOW.  WIth a fairly hard pull-up resistor of 1K Ohm you'd only need a contact resistance on the order of 50 Ohms to ensure the signal is read as LOW.

Perhaps the 'signal' is actually a 5V power line.  Get yourself a multimeter and measure the current coming through that pull-up resistor.  If it is delivering more than 20 mA then maybe it's not intended to be driven low.  If it is delivering less than 20 mA you should be able to connect it directly to an Arduino pin and drive it LOW as needed.
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cianide

Measuring the current was a great idea.

The circuit rests at 10 volts actually. It is only taking 2.4 ma to ground the circuit.

I don't understand why just grounding it with the digital pin won't work.

kf2qd

Okay - then pin is actually supplying 10V. And the Arduino is rated for 5V. Is the signal expecting a pulse? Or to be constantly held low? And how will the signal behave at 5V? Get a relay and drive it with the Arduino. You will get much more predictable behaviour.

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