I want an I/O pin to return current in a circuit, similarly to the function of ground.
Which of these will achieve what I require?
pinMode(pinnumber, OUTPUT)
digitalWrite(pinnumber, LOW)
or
pinMode(pinnumber, input)
Your first snippet is the correct solution.
pinMode(pinnumber,OUTPUT)
digitalWrite(pinnumber,LOW)
Be careful though, you can only sink up to 6mA or 9mA per pin (as per the documentation ["Input and Output" section], I never tried more). If you need more current, use a transistor (this looks like a good example, you just need to invert the output pin to HIGH).
When the pin is configured as input it is supposed to be high impedance, not what you want.
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Thanks, the current also comes from the IO pins of Arduino. Therefore, i don't think 40mA limit will be a issue. – rajat Mar 5 '14 at 10:30
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@rajat Doing some sort of LED matrix ? Be careful, assuming you plug (for example) a high current LED between two pins (at least without a proper current limiting resistor), you could still damage the chip. Not even mentioning the case where you create a short circuit. – FredP Mar 5 '14 at 10:35
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It is a pressure sensor matrix, it has 10 16:1 multiplexers. The current only comes from the Arduino USB cable and no external power supply.Therefore, i don't think high current will be a issue. Can you shed some light on what possibly can cause a short circuit? – rajat Mar 5 '14 at 10:37
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@rajat something like that would create a short if pin "1" and "2" are connected :
pinMode(pinnumber1,OUTPUT); pinMode(pinnumber2,OUTPUT); digitalWrite(pinnumber1,LOW); digitalWrite(pinnumber2,HIGH);PS : do not try this at home, do not harm innocent arduini, do not sue me, etc... – FredP Mar 5 '14 at 10:43 -
2I was a bit surprised by the 6/9mA number. Turns out you’re correct for the Arduino Due, but for the AVR based Arduinos (Uno, etc), which I suspect are still in the vast majority, that number is more like 40mA. – microtherion Mar 6 '14 at 21:55
pinMode(pinnumber,input)is placing the pin in the "third state" of the pin, which is also called "high impedency". It's basically like if the pin was not connected to the circuit, like a ohmmeter does. – zmo Mar 5 '14 at 13:31