battery powered?

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

1. James VargaGuest

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
battery.

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
use?

The other thing I would think of asking is that is there an easy
way/schematic for charging a battery like this?

2. Watson A.Name - \Watt Sun, the Dark Remover\Guest

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
life.

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. Alaric Snell-PymGuest

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.

http://www.maxim-ic.com/

Check around:

http://www.maxim-ic.com/solutions/battery_management/index.mvp

ABS

4. Brian DrummondGuest

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. John WoodgateGuest

I read in sci.electronics.design 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. ThorntonGuest

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.

NT

7. James VargaGuest

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. Spehro PefhanyGuest

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

10. James VargaGuest

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 WGuest

It came up with this:

http://www.qprox.com/products/qtouch.php

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
application.

HTH

12. John FieldsGuest

---
Dunno...

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. ClarenceGuest

http://www.mpja.com/productview.asp?product=12568+OP

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

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

14. ClarenceGuest

Not what?

"Not - "not a representative " OR???

16. ClarenceGuest

Spelling error! That is "Nut - nut." ;-)

17. Spehro PefhanyGuest

Not not. ;-)

Best regards,
Spehro Pefhany

18. Ken MoffettGuest

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!

19. Watson A.Name - \Watt Sun, the Dark Remover\Guest

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.
;-)