question about "quiescent current"

I’m interested in using a LiPo battery for my arduino project, which will have long periods of time where I want the project to “sleep” and consume little power.
I’m looking at products like this:

which will boost the LiPo voltage to 5V, which can power my arduino (and modules). It claims to have a “quiescent current < 55uA”.
I’m wondering what that means, exactly. Does that mean:
a)-when nothing is attached to it, it will draw < 55 uA?
b)-when the enable pin is brought low, it will draw < 55 uA?
c)-when my arduino is attached, and in “power-down sleep” mode, and drawing 23 uA, then the boost board will be drawing close to 55 + 23 = 78 uA?

What I’m really interested in is achieving something like (c), but I don’t have experience with these kind of boards, and was wondering if someone knew more about it.

(a) and (c) are correct. The data sheet should tell you about (b).

Just power the Arduino directly with the battery. If you use 3V modules, you may need a 3V low dropout regulator. An outstanding guide to low power operation is here.

Thanks much for the info.
Yeah, I would power the arduino directly off of the LiPo, but the problem is that I also want the battery to power other modules, like an ultrasonic sensor, which seems to require 5V, and if the US sensor is running at 5V, I think it would be sending digital signals to the arduino at too high a voltage (e.g. if the LiPo is putting out 3.5V, Vcc for the arduino would be 3.5V, and the 5V digital signal from the US would be too high, wouldn't it?).
given that, it seems like my choices are:
-power the arduino and the modules off of the 5V boost board, or
-power the arduino directly off the lipo, power the modules off of the boost board, and drop the modules' digital signal through a logic level converter...
Unless anyone has some brighter ideas :slight_smile:

If the sensors need 5V it makes sense to have the entire system running on 5V. You probably can't do much better than the step-up regulator you have chosen.

snapster:
Unless anyone has some brighter ideas :slight_smile:

Slightly bigger LiPo battery?

We're talking less than 2mA per day.
Six years on an average 2ah LiPo battery.

Did you also calculate self-discharge of the LiPo into that formula.
Dunno. Might be more than 78uA.
Leo..

Self discharge is a very real concern. Something else that needs to taken into consideration is battery capacity if you are using it someplace with temperature extremes - this is often overlooked when it needs to be considered. Your comments about low power while sleeping etc. has the feel of something that is going to be put somewhere and if that somewhere is outside for example, temperature is a real consideration. If this is going to reside in a house for example, then the temperature issue is not as big.

This system is intended to operate outdoors. It has a solar cell to recharge it.
Does anyone know how modules are typically powered down when you want to hibernate? The ping sensors I have do not have a shutdown mode, and continue to draw non-negligible current even when not pinging. When in use, they draw 30 mA. I read that the max current from a digital pin on the arduino is 40 mA. Does this mean that I could power the ping sensor, and have the ability to completely shut it off, with a digital pin?

40 mA is the absolute maximum current draw for a port pin, above which it will likely be destroyed. It is not a good idea to draw more than 20 mA.

Use an external transistor + base resistor to switch loads higher than 20 mA, and be sure to use a LiPo charger with the solar cell.

Ah, yeah, sounds like I'll have to resort to that.
Yeah, I'm using a little board that adafruit makes that was designed to solar-charge a lipo.