Power usage of a float switch used as sensor?

Projects General Guidance
1

Hi all.

I'm planning to use a float switch to keep an eye on my water level in an IBC tank. Wil be using this model

Now I can do two things.

1, have it mounted this way that the switch will be closed most of the time and opened when the water level rose to a certain level.

2, the way around, mounted that the switch is open most of the time and closed when the water level rose to a certain level.

The main question is, how much power will the switch use while closed compaired to open? In my code I'll look for the state of the switch once per second.

2

Using an UNO, the one I know best, and alternative 2 looks like the best provided that the level spends more time below swtiching point than above. The difference is marginal.

3

How big of a difference is basically what I want to know. If I know how big it is I know if it it marginal "enough" for me to not matter.

Wil be using a nano. The 10 meters of telephone cable show 30ohms. Maybe that's also important info...

4

R=U/I

I=U/R

I=5volts/30ohms

I= 0,166 ampere = 166 milliampere?

Some old highschool stuff staring to float around in my head, probably wrong....

5

I don't know the Nano but for an UNO there is a built in PULLUP resistor of 10 kOhm. 5 volts, or maybe 3.3 volts divided by 10 kOhm…. 0.5 mA when being Active.
The 30 ohm of the cable can be ignored.

6

Railroaded thanks for the fast reply.

The nano also has a buildin PULLUP register I think. Not sure, will look it up to be sure.

Still not clear to me why the 30 ohm of the cable can be ignored. Resistance "consumes" energy? So just to sense if the switch is closed or open does not "use" energy?

7

The typical resistance of internal pullup is 10 kOhm. +- 30 Ohm..... not significant.

8

All the IO pins on the Uno have a 30K to 50K internal pullup.
Wire your switch to connect an IO pin to GND when closed.

V/R = I.
5V/(30000 + 30) = 0.16mA

The Power LED on the Uno board will be drawing more than that.

9

Yes, you can enable pull up on the pins of a Nano. And I think they are more like ~30k.
That will "consume" the insignificant current of 5/30000 = 0.166mA, or 5/30030 = 0.166mA if you add that 30ohm to it (the cable is in series with the pull up resistance).
That pull up current is insignificant if you compare that to the ~30mA the Nano itself draws.

Why do you actually need a micro to "keep an eye on the level".
Leo..

10

Thanks all. All clear now thanks for helping out

11

@ C R
Thanks for the update. I could have measured that current to be precise.

12

Leo, I use the arduino nano since that is what I have available here at my brothers homestead.

A 433mhz transmitter will send the state of switch to the house. There a barebones arduino will light a led when the tank is almost empty (and almost full)

Could do with way less I guess but this are components I allready know and I got it working with some simple push buttons. These will be swapped with the float switches.