Can an Arduino Sink More than it can source?

I am simply wanting to use my arduino to flip on a 5v relay. When I hooked up the relay to a multimeter I saw that at steady state it drew 70-80 mA. In the uno's schmatics it saw that a pin can only source 40 mA. If I were to reverse it and put one side of the relay to the 5v pin and the other to my digital pin would that make any difference? Basically will a digital pin sink more than it will source?

The other idea is to take connect 3 pins together and set them all to HIGH and let them share the load.

Please help me to understand. I guess I could add a transistor to switch on the relay but that adds complexity and Im not exactly sure how to go about that.

You must use a transistor and a fly-back diode parallel with the relay. And you need a resistor from Arduino output to the base of the transistor.

To answer your question, the Arduino can sink the same current as it can source. It is about 20mA. The 40mA is some number in the datasheet, but not to be used for real.

Using a few pins together and turning them on at the same time is possible. You could use 8 pins of a single PORT. You have to use direct port writing for that. But one small mistake, or using pin 13 (used by bootloader to blink led) and the Arduino is damaged.
A design that has such a self-destructive option is a very bad design. Stay away from it.

So I repeat: You must use a transistor.

Okay I am willing to try with a transistor. I don't have really much experience with a transistors but is the below picture something good to go off. I guess I would take the camera ground and connect that to the arduino gnd and take the camera switch and connect it to the gnd side on my relay??? Is that correct? Where would I put the mentioned diode? Also is this a npn transistor??


http://d2lg1iac45z1vf.cloudfront.net/wp-content/uploads/2010/07/Arduino_CAM_Hack_breadboard.png

Wait I think I found a better image, is this what you are talking about??

TIP120 ? REALLY ? Why don't you use a hammer to kill an ant ? No , a 2n2222 or 2n3904 should be fine. Your first one looks correct.

The diode should be acrosss the realy coil not the transistor.

The diode should be acrosss the realy coil not the transistor.

Oh, and that too... (the diode should always be across your LOAD , not your switching device. )