Hello,

I am trying to build a charging case to carry several devices such as a phone, tablet, laptop, etc. The charging side of this is no big deal, but i would like to add some LED indication on the external side of the case to indicate charging status. Keeping it simple I just want to show charging (Red), and complete (Green). I know i can use a current sense resistor to indicate charging easy enough, but how could i indicate when the device is fully charged?
Any help on this would be greatly appreciated.

Thanks,
Joe

 

Perhaps use a comparator to compare charger voltage with battery voltage?

 

Just stick one of these in it (or one like it, there are hundreds to choose from at similar prices from similar suppliers).

Wire it in-series with a momentary "push-to-test" button so that it doesn't run the battery down...

Way more useful than single LED or even LED bar-graph type displays...

 

Given that the phone, tablet and laptop each have internal monitoring arrangements to reduce/switch off the charging current when charging is complete I would think all you need is a current sensor or three.

 

Unfortunately a current sense wont give me a done indication. It lights up when there is current being drawn through the sense resistor but shuts off when the charging circuit has completed the charging. So if the case is closed there is no way to determine if the device has been charged or is simply unplugged. The internal charging circuits make it complicated because i have no access to the direct battery voltage to use a comparative circuit. Which means the volt meter will also be useless because i have no voltage to read from. I am looking into using a flipflop and some logic gates to try and get this to work. Will let everyone know how it turns out.

Any other ideas are appreciated, and thanks for the previous advise. It always helps to throw ideas around.

 

Hook one of these (per charging device) up to a comparator:

http://www.ebay.co.uk/itm/Adafruit-...rent-Sensor-/181709646057?hash=item2a4ebd28e9

I can't think of any other way to reliably do this.

 

Keep in mind that voltage regulators / references are essentially comparators and they can be easily configured here for your application.