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Domino & Battery Shield


I have this Arduino form li-on battery backpack -

Now I’ve hooked the power loop up properly and that’s working. What I’m curious about is how to go about reading the power status.

From what I’ve seen on a post about the pack:


The status pin is actually just tied directly to the lithium battery’s positive terminal. Measuring the voltage here you can estimate the life of the battery.

Those schematics need to be updated to include the 3.3v and status. I will try and post more updated ones.

The 3.3v is rated for 100mA and the 5v is rated for 500mA continuous.


May 15, 2008 7:47 AM"

However how do I go about reading this? Can I use the Domino directly or do I need some other components in-between?


There is not good documentation on this shield! All I could find is a blog with 1 million comments!


I’ve read that page many times, it explains the power circuit and doesn’t really explain how to use the status pin…


I believe you have already provided the answer.

Which I think means you could use a voltage divider to measure the voltage. (Since it is connected to V+ of the battery)

More info in the beginners guide and on my blog.

Page 31 in beginners ebook:

My blog:

IMPORTANT NOTE: before connecting stuff to the analog in, please make sure you do not exceed 3.3Vin.


Now that’s more like the response I needed (the voltage divider etc) thanks :slight_smile:


No problem. Don’t forget the note: make sure you do not exceed 3.3v on Vin.

Good luck. Let us know if you need help :wink:


Yeh from my multimeter, seems to be putting out 4.06v at full charge, not the 3.3v it’s supposed to :confused:


Don’t you also have to limit current on input pin to <= 100mA?


Maybe I’m misunderstanding, but you need more than 3.3V going into the VIN pin on the FEZ since VIN passes through Vregs.

You should not exceed 3.3V on 3.3V, likewise, you should not exceed 5V on 5V. You should not exceed like 9V on VIN.


What is the limits/cutoff volts on VIN regulator? Will it, for example, boost a 4v source when battery supply falls?


The Vregs on the FEZ boards are not step voltage up. You need to feed them the required voltage + a little more to get a clean output voltage.

There are no limits that will actively protect the device against overvoltage.


However this isn’t going in on the VIN at all, instead this shield pumps out 5v and 3.3v and works by directly attaching it to the 5v of the board bypassing VIN completely.

The problem was with the status pin, research indicates it gives out about 4v. From previous help further up I’ve now set up a volt divider and it pumps about 2v into An1 which I can now read nicely.


“However this isn’t going in on the VIN at all, instead this shield pumps out 5v and 3.3v and works by directly attaching it to the 5v of the board bypassing VIN completely.”

Yes, my ADD took over and I changed subjects a bit.
Back to your matter. As ref is hooked directly battery, that means your battery is showing 4v also. Unless there is some other circuit going on. Either way, sounds like you got it. I would also limit as much needless current (via a resistor) as you can. No sense running any more current into the pin then you need for a reading I would think.


Cool! And fez is powered from this pack too?


Yes the pack dishes out both 3 and 5v charges, however you only need to supply the 5v and you get 3v automatically which is nice, saves on a wire :slight_smile:


I’m curious, is there any way to know where the power is coming from? I’m guessing I can check the USB to see if it’s connected or not?


Not that simple in my mind. I have a USB power supply in my car that I have occasionally run a Fez from. That won’t show up as a USB connection (to a host) because it’s only supplying power, not data.


I was thinking he wanted to know via code on the FEZ if the power was coming from the 5v usb or the 5v in/out-pin (i.e. battery power). I suppose if you had a compeling reason to do this, you would use a vreg breakout that powers the fez from batt or USB and then expose test pads on it. This would also be functional as you can leave your battery attached and charge it from usb 5v or external 5v. Something like slight circuit bending of :


Yes, agreed - whether power was from USB or not. The only thing the current USB client shows is if it’s connected to a host, so my point was you can’t rely on that to tell you if you’re externally powered.

I think what we’re approaching here is a situation where if you have a very specific reason for wanting to do that then you’re going to have a very specific hardware platform that will provide that info to you. I can totally see that for solar powered remote sensors or similar where you want to control your behavior based on power inputs and charge levels etc. In general I suspect that most people don’t really need to know, their application won’t change dramatically for different power scenarios.

Lloyd, perhaps you can tell us whether the soure of power will be “critical” to your usage or not; since you said you were curious, I suspect that it won’t be a deal breaker for you if you can’t.


This chip would seem ideal for this and general purpose battery/supply/charger board. Wish SF would have used it.

It can determine if supply is usb or battery and switches automatically between sources and can charge battery at same time your sys is powered via usb. Perfect. Only issue is it is a QFN. So takes it passed hobby hacks. Will have to wait for SF to upgrade their breakout.