I want to incorporate an 12 eTape Liquid Level Sensor + extras : ID 464 : $39.95 : Adafruit Industries, Unique & fun DIY electronics and kits into my project but I want to use the 5v pin for other things as well, so I was wondering, does the sensor only get powered on when I make a call to it in my code? Say I wanted to use a DS18B20 Digital temperature sensor + extras : ID 374 : $3.95 : Adafruit Industries, Unique & fun DIY electronics and kits as well, would I make a call to the water sensor, get that reading, turn it off, then make a call to the temp sensor? Thanks for any help guys.
You want to use what 5 volt pin?
How are these sensors wired to your arduino?
do you have a sketch of their sampling?
Why are you concerned, you have many input pins. Are you worried about power drain? How much power does these two items require?
If you are running off a small battery, power drain may be a concern. What is your power source.
does the sensor only get powered on when I make a call to it in my code?
No. It is normally powered all the time.
Unless you design a special circuit to remove the power when you want it off. This is not something that is normally done with a project.
Are you trying to disable the input from the flex sensor or something like that? Only get readings when you need it? More info please
Now, I may be misreading your post, but when you say you want to use the 5V for other things, it sounds like you think if you plug the 5V into the sensor, that you can't use it for anything else. Think of the common breadboard with two rows on each side. The black row is typically connected to ground, and the red to power (5V in this case), every device draws from the common power pool, and as long as the total watts does not exceed the rated capacity of the machine, all is fine.
Are you so close on the power that you literally can't afford the small power the force sensor draws all of the time? If so, it may be time to rethink your power envelope. But if that is not feasible, then you need something like an semiconductor/MOSFET, etc. to cut off flow of power to the sensor (and of course you now have to figure out how much power the semiconductor draws)
@MichaelMeissner, good thoughts. But the OP has not given us info that I requested yet. If the power requirments are low enough, he can provide power on demand from an output pin (60ma for 1/2 second). No external mosfet needed. We have not yet enough info to make a suggestion.
BTW, I have powered external devices up to 70ma for 1/2 second from a I/O pin with success.
BTW, I have powered external devices up to 70ma for 1/2 second from a I/O pin with success.
But with damage to your arduino.
It is hard to say how much damage has been done but you will have increased the statistical chances of an early failure of your chip.
No, there has been no damage to my Arduino. It was designed to accept that sort of loads.
jackwp:
No, there has been no damage to my Arduino. It was designed to accept that sort of loads.
Yes you have. The fact that it appears to continues to function does not mean it is not damaged.
And no it hasn't.
According to the data sheet 40mA is the absoloute maximum current, even this over time causes damage.
Of course you probbly know more about this chip than the manafacaturers so why not write to them and tell them about the "error" in their data sheet.
The fact that it appears to continues to function does not mean it is damaged.
I think you meant "The fact that it appears to continues to function does not mean it is not damaged."
But yes, absolutely agree with you Mike.
Yes my iPad again. sorry, corrected post now.
The only way to assess damage is to decapsulate the chip and examine it under a microscope, preferably an electron one. And I am assuming that jackwp hasn't done that.
We should all have as much concern for the human body as we do for a $5 chip.
If we decided to not do anything to our human body that is not guaranteed to be safe, then I think most of us would live longer.
But, If I had a coke today, and thought I was still ok, I could ask to be dissected and reviewed with an electron microscope, and probably find that that coke did degrade my body.
The point being, the chip has a guarantee that 40 ma will not hurt it. I don't have much money, but If my chip died, I could replace it. If my body dies, it would not be so easy. So worry about the big things, and don't sweat the small things so much. You will live longer.
the chip has a guarantee that 40 ma will not hurt it
But you weren't talking about 40mA, were you?
You've not been here long, jackwp, and haven't had to field the near-daily questions about smoke because "the output current is limited to 40mA so why is my Arduino dead?", so when a member with in excess of 700 posts says it's OK to draw more, us old-timers naturally react to limit the damage.
It's just another "live-longer-through-less-stress-mechanism" we employ - not everyone has such easy access to spares or cash as you do.
I was trying to learn more about this smoke problem. Based on your info
the near-daily questions about smoke because "the output current is limited to 40mA so why is my Arduino dead?"
I have looked around for these problems for the last 3 days, and I have not located one. I must have missed the post.
Can you steer me toward the last couple of such posts.
Thanks, Jack
You're from Texas - I'm sure you're no stranger to hyperbole for dramatic effect 
@AWOL
I had to look up that term. You are right, I am no stranger to people lying, I try to not do it myself, but am not always successful.
So, not a post ever day?
How about weekly, or monthly?
Or ever?
I assume you have never used more than 40.00 ma on an output pin.
Maybe we need to run a test. If you have a $5 chip, and a PayPal account, I will pay you for your chip if you test it to see how far it can go before burnout.
Are you game?
I had to look up that term.
I'm sorry.
lying
You need to look it up again.
How about weekly, or monthly?
Or ever?
Yes, really.
Noobs really do read the absolute maximum rating as though it something beyond which the chip will simply give up and say
"No, I simply will not supply any more",
rather than the actual
"I will cause heat-stress fracturing of my output stage and may vapourise my bond wires"
I assume you have never used more than 40.00 ma on an output pin.
You'd be wrong, I certainly have, but never intentionally.
Got the salvage bin to prove it - usually a slip of the screwdriver or an unexpectedly conductive worksurface.
(I've still got my first Duemilanove I bought in early 2009, and it all still works)
Besides, we're not talking "40ma"[sic], we're talking the "70ma"[sic] you quoted.
Are you game?
No, that's usually an invitation to be fired-upon by shotgun-wielding toffs.
@AWOL
I had to look up "toffs" to. LOL, and I am surly not one. I am just an old dude (a bit older than you), with a dog, 3 ducks, a garden, and living only off my social security check (low as it may be). I only drive my truck to town once a week for supplies (Wallmart).
I think maybe we got off on the wrong foot. I am ready to call a cease fire if you are. Are you game?
jackwp:
The point being, the chip has a guarantee that 40 ma will not hurt it.
No that is not what the data sheet say. It says of the 40mA absolute maximum
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent dam- age to the device. This is a stress rating only and functional operation of the device at these or other conditions beyond those indicated in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
The limit is a bit soft but 30mA should be considered the maximum for reliable operation although some people read the data sheet as saying a 20mA maximum.
Yes there is a point of view that says, this is only a hobby so it doesn't matter if a smoke a chip and that is fine if you know that it is a risk you are taking. But take that decision from a position of knowledge.
I am ready to call a cease fire if you are
I'm up for that. 
Ok, cease fire. We can call this thread closed.
The OP has never returned. Did we scare them off? LOL