battery powered?

noob I

IC)

constant

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.

Reply to
Watson A.Name - "Watt Sun, th
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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?

Reply to
James Varga

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.

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Check around:

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ABS

Reply to
Alaric Snell-Pym

crossposting to 6 groups is too many! reply to sci.electronics.basics

please cc me > Okay - I've got a simple project going on here and being a bit of a noob I

Sounds about right.

How are you controlling the current? Internal resistance of the battery? Then you may have a problem using NiMH cells, see below, as they have low internal resistance.

Problem. Can you go to 5.6 or 6.5 mm? That increases your options a lot. How much width do you have?

Don't you mean a 10 nF cap?

If the led's aren't lit it will last a long time (years) if 620mA primary (= non-rechargeable) cells are used - however, if you use NiMH cells they will only last for perhaps six months, as they will self discharge.

When the led's are lit it will last 100 hours, if you get the current right.

Exactly what kind of battery were you looking to use?

Blue led's take a higher voltage than ordinary led's, and will probably need at least three cells (unless you use lithium primary cells) - some will need four or even five! What led's are you using? It makes a difference, some work at around 3 volts, some need over 5 volts.

Generally, button cells are not rechargeable, although there are some new NiMH ones that are - but their voltage is lower, requiring more cells. They are quite large though, and a 600ma cell is 6.5 mm high and about an inch wide by an inch and a half long. They do not have primary replacements (you can't take them out and put a non-rechargeable cell in, because you can't get a non-rechargeable cell the same size).

Charging them can be done in several ways, the easiest is a low current charger that will take half a day to charge and will not do too much damage if left on a bit too long.

If people aren't going to want to think about whether to charge it or not, and just leave it plugged in, there are several ways - first, a slow trickle charge. Much the same as above but it will take a day to charge, and not really recommended, although it will work and is simple and cheap. Better, an hour per day charger on a timer, with a switch to charge for 12 hours when needed.

Then you get into the area of battery state sensing chargers, which can take you anywhere you can afford. How much is the finished item likely to be worth? Are you going to be selling it?

How often will the leds be lit? How often do you want to charge it?

All that may be a bit too much theory, it is often better in such projects to just try it and see what happens. You may blow up a few parts, buit they aren't that expensive. Do try to measure the led current, and get it close to 20 ma by adding cells or whatever.

Reply to
Peter Fairbrother

If the led's aren't lit it will last a long time (years) if 620mA primary (= non-rechargeable) cells are used - however, if you use NiMH cells they will only last for perhaps six months, as they will self discharge.

When the led's are lit it will last 100 hours, if you get the current right. ^^^ Oops, should be 10 hours. Brainfart, sorry.

--
Peter Fairbrother
Reply to
Peter Fairbrother

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

Reply to
N. Thornton

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

Reply to
Brian Drummond

I read in sci.electronics.design that James Varga wrote (in ) about 'battery powered?', on Wed, 6 Oct 2004:

In parallel?

What is the duty cycle (time on/total time)?

What sort of 'button cell'? Only a few types can be charged.

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Reply to
John Woodgate

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Reply to
John Fields

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

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Reply to
Spehro Pefhany

Okay - I had a look around and couldn't find any 2mA LED's - only the typical 20mA and 30mA - any suggestions?

Reply to
James Varga

Thanks John but all I see there are red, yell, and green ones - I need a blue one - or do they exist?

Reply to
James Varga

--
Dunno... 

You might want to Google around for "high efficiency blue LED" without
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Reply to
John Fields

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

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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

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Reply to
Graham W

See:

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

See:

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

Love these little chips!

Reply to
Ken Moffett

Or these are cheaper @ 0.45/each for 20/BIN:

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I'm not.

Best regards, Spehro Pefhany

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Reply to
Spehro Pefhany

Not not. ;-)

Best regards, Spehro Pefhany

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"it's the network..."                          "The Journey is the reward"
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Reply to
Spehro Pefhany

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

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

Reply to
Clarence

Not what?

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

Reply to
Clarence

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

Reply to
Clarence

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