Need Help With LED indicated charging case

Discussion in 'The Projects Forum' started by jbrant308, Sep 22, 2015.

  1. jbrant308

    Thread Starter New Member

    Sep 22, 2015

    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.

  2. TheButtonThief

    Active Member

    Feb 26, 2011
    Perhaps use a comparator to compare charger voltage with battery voltage?
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
    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...
    Last edited: Sep 22, 2015
    absf and cmartinez like this.
  4. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    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.
  5. jbrant308

    Thread Starter New Member

    Sep 22, 2015
    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.
  6. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
  7. dannyf

    Well-Known Member

    Sep 13, 2015
    Keep in mind that voltage regulators / references are essentially comparators and they can be easily configured here for your application.