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battery powered?

Discussion in 'Electronic Components' started by James Varga, Oct 6, 2004.

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  1. James Varga

    James Varga Guest

    Okay - I've got a simple project going on here and being a bit of a noob I
    need some help ;)

    I've got three x 3mm blue LED's hanging off a QT110 (touch sensitive IC)

    The QT110 consumes 20uA

    Each LED consumes (i think) about 20mA.

    I only have 5mm height to put this in so I'm stuck with a button cell

    The only other thing there is is a 10uF cap.

    So help me out - how long would a battery of say 620mA last under constant

    The other thing I would think of asking is that is there an easy
    way/schematic for charging a battery like this?
  2. You're going to catch hell for crossposting to so many newsgroups. Noob
    is right.

    You didn't say what kind of button cell, or what voltage. But lithiums
    such as CR2032 are not rechargeable. Big time No-No. If you have
    enough room for a touch pad, then you should have enough room for
    several cells, which should give you higher capacity and longer battery

    The battery life depends highly on the LEDs and how long they are turned
    on. You gave no indication if they were on constantly, flashing, or
    alternating, like a marquee on a theater.

    If you limit the length of time the LEDs are on by flashing them briefly
    for a fraction of a second, every second or so, then the average current
    consumption will be much lower and the battery life much longer.
  3. Is that a 620mAH battery? If so, then the total consumption will be
    about 3x20mA + 20uA = about 60mA. A 620mAH battery would then last for
    620 / 60 = about 10 hours. But the specified power consumption of ICs
    can often be under "ideal circumstances" and rather idealistic. It would
    be best to take 10 hours as a maximum, and if it matters, build the
    circuit and connect it up through an ammeter to see what it really draws.
    Yes! You can get ICs (Maxim sell nice ones IIRC) to manage a battery.
    You connect a battery, an external power jack, and the device to various
    terminals on the IC, and it intelligently switches power to the device
    between the battery and external jack, and charges the battery, as
    appropriate. Some of them require an external power transistor, but if
    your device is low consumption, I think that can be done without.

    Check around:

  4. So the current consumption looks like ... 60mA. But...
    What is the battery voltage?
    If it is less than the 4V or so that blue LEDs consume, you will have to
    provide some way of stepping up the voltage.
    If the battery is about 1.5V, you'll need to roughly triple the voltage,
    and that will roughly triple (or quadruple, allowing for losses in the
    voltage converter) the current consumption to, say, 200-250mA.

    Giving around 3 hours at best from the button cell.

    - Brian
  5. I read in that James Varga <>
    In parallel?
    What is the duty cycle (time on/total time)?
    What sort of 'button cell'? Only a few types can be charged.
  6. N. Thornton

    N. Thornton Guest

    Theres your problem! Try ultra low current LEDs, ie either low current
    ones @2mA or else ultrabrights run at even lower. Also try flashing
    them, or using LCD if possible instead.

    With no knowledge of your app, cant make any more useful suggestions.

  7. James Varga

    James Varga Guest

    Theres your problem! Try ultra low current LEDs, ie either low current
    Okay - I had a look around and couldn't find any 2mA LED's - only the
    typical 20mA and 30mA - any suggestions?
  8. Just use an LED that is very bright at 20mA, and it will be quite
    acceptable at one or two mA.

    Best regards,
    Spehro Pefhany
  9. John Fields

    John Fields Guest

  10. James Varga

    James Varga Guest

    Okay - I had a look around and couldn't find any 2mA LED's - only the
    Thanks John but all I see there are red, yell, and green ones - I need a
    blue one - or do they exist?
  11. Graham W

    Graham W Guest

    I've been reading this thread and I decided to Google for QT110.
    It came up with this:

    from which it appears, on cursory examination, that the capacitor
    is a 10 nF ceramic. The data there comments that:"Most QT110
    family devices are designed for human touch; some, like the QT110
    and QT118H even include piezo beeper drive logic"

    I haven't found a spec for the /OUT pin but the chip is spec'ed for
    +3 to +5vdc supply.

    The blue LED I have here will light quite nicely as an indicator
    when drawing 0.5mAmps. But whether the /OUT pin can drive
    three of them I don't know.

    The OP should be aware that LEDs are not like filament bulbs
    and that their operating current is part of the design of the

  12. John Fields

    John Fields Guest


    You might want to Google around for "high efficiency blue LED" without
    the quotes, or take Spehro's advice and get a superbright 20mA one and
    run it at 2mA.
  13. Clarence

    Clarence Guest

    $1.25 Each. 3900mcp, 4 volts, 20ma, 5mm dia.

    I am ONLY a customer not a representative of this site.
  14. Clarence

    Clarence Guest

    Not what?

    "Not - "not a representative " OR???
  15. Clarence

    Clarence Guest

    Spelling error! That is "Nut - nut." ;-)
  16. Not not. ;-)

    Best regards,
    Spehro Pefhany
  17. Ken Moffett

    Ken Moffett Guest

    Bottom of page 5, right column.
    QT110 and QT110H sinks 5mA and sources 1mA

    Middle of page 6, right column
    QT110H sinks 1mA and sources 1mA

    Love these little chips!
  18. I'm also a satisfied customer of MPJA. However, one needs to remember
    the following:

    MPJA sells surplus, so unless they say that the part is new, one should
    assume that the part could be surplus or used.

    LEDs in general, and even more so with blue and white, are recent and
    advancing technology, so what you may save on less expenaive LEDs may be
    eaten up by disappointing performance. Or worse, as I found when I
    bought a few LEDs: the blue ones became intermittent after a few tens of
    minutes of operation.

    I've since purchased blue LEDs directly from Nichia, and found them to
    be very reliable and of excellent quality. Just a satisfied customer.
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