10 leds running off 2 AA batteries
Donwill
series giving 3 volts or thereabouts presumably.
I was a bit sceptical about the life of the batteries so I left them on
24 hrs to check, I was surprised that they lasted over a month which
makes them very useful as party lights in a damp conservatory, let's say
running them for 4hrs a day which should make them last for 6 months
perhaps.
I got to thinking about dimming them, a series resistor would surely do
that, but it would reduce the battery life by warming up the resistor.
Now you can dim filament bulbs by using an astable multivibrator and
varying the mark to space ratio, relying on the chopping frequency and
the time constant of the filament to provide a non flickering and
dimmable light.
Doing that to an led would cause flickering of the light but would the
relativly slow response of the eye smooth out the flicker? as in film
movies which I think have to be in excess of 25 fps in order to fool the
eye.
In the interests of battery life, are there any dimmers of this type
available for leds?
Cheers
Don
Andy Burns
> you can dim filament bulbs by using an astable multivibrator and
> varying the mark to space ratio
> Doing that to an led would cause flickering of the light
Not perceptible if you do it at several kHz
brass monkey
"Donwill" <Donwill...@invalid.invalid> wrote in message
news:7msk37F...@mid.individual.net...
A 555 timer will prolly do the job
http://www.kpsec.freeuk.com/555timer.htm
Of course, the cost of your time in making it would buy a good few batteries
;)
Adrian C
> A 555 timer will prolly do the job
> http://www.kpsec.freeuk.com/555timer.htm
> Of course, the cost of your time in making it would buy a good few batteries
> ;)
A bit of slightly opaque paint dabbed over the LED's would be even cheaper.
--
Adrian C
Donwill
Cheers
Don
Donwill
Don
Frank Erskine
<Donwill...@invalid.invalid> wrote:
>I purchased a string of 10 Leds powered by 2 AA batteries connected in
>series giving 3 volts or thereabouts presumably.
>I was a bit sceptical about the life of the batteries so I left them on
>24 hrs to check, I was surprised that they lasted over a month which
>makes them very useful as party lights in a damp conservatory,
Sounds a fun place to have a party :-)
--
Frank Erskine
Adam Aglionby
Pulse width modultaion, subject of several U.S. patents in relation to
LED dimming but thats a rant for another time, 555 as suggested can do
it, fly swimming slowly in ointment is V drop, only have 3V to play
with , drop 0.7V across a semi junction, even low Rds Fet will drop a
bit.
Couple of strings in series to get voltage up and then dim them.
Cheers
Adam
gazz
news:hadig5ph6b0p7bijb...@4ax.com...
maybe it's a BDSM party and the conservatory is the code word for his
dungeon :)
pretty easy to dim leds as mentioned, but another circuit you could build is
the joule theif, just search google for led joule theif,
these are pretty simple, an inductor transistor and resistor, and you can
drain the very last dregs from a battery lighting the led's up,
common uses are to run a white led off a 1.5 volt practicaly dead battery,
Clive George
news:f082c9a4-231f-4d45...@37g2000yqm.googlegroups.com...
>Pulse width modultaion, subject of several U.S. patents in relation to
>LED dimming but thats a rant for another time, 555 as suggested can do
>it, fly swimming slowly in ointment is V drop, only have 3V to play
>with , drop 0.7V across a semi junction, even low Rds Fet will drop a
>bit.
At which point maybe the resistor may be as efficient, depending on current.
mick
This gets to be fun if you are restricting your supply to 3v. Here's a
dimmer for 12v: http://www.reuk.co.uk/LED-Dimmer-Circuit.htm
You may be able to get it to work using a CMOS 555 (which works down to
about 1.5v) and, maybe, a MOSFET such as 2N7000 instead of the transistor
to give better efficiency at the low voltage. You could decrease C1 to
increase the frequency if you get any flickering. R2 can be omitted if a
MOSFET is used.
--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.
Harry Bloomfield
> Now you can dim filament bulbs by using an astable multivibrator and varying
> the mark to space ratio, relying on the chopping frequency and the time
> constant of the filament to provide a non flickering and dimmable light.
> Doing that to an led would cause flickering of the light but would the
> relativly slow response of the eye smooth out the flicker? as in film movies
> which I think have to be in excess of 25 fps in order to fool the eye.
> In the interests of battery life, are there any dimmers of this type
> available for leds?
It works, but for LEDs you need to increase the switching frequency to
be much higher - say around 1Khz. The filament in a lamp also takes
some time to heat up and cool down, giving it some persistence.
--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk
NT
> "Frank Erskine" <frank.ersk...@btinternet.com> wrote in message
The joule thief pulses, so you can incoporate dimming by delaying its
switching on each cycle.
NT
Andy Champ
>
> It would be easy to knock up electronics do do so.
>
> A lot of vehicle lights are dimmed by pulsing them. If you observe LED rear
> lights and turn your head there is often a flicker. When the same lights are
> used as brake lights the flicker disappears as they are then fully on. The
> frequency used must vary as some lights are more noticably flickery than
> others.
>
> I'd go for at least 100Hz to minimise the flicker. Much higher is easy to
> achieve.
>
Go up in the kilohertz range, or you'll annoy some people.
As many car manufacturers are currently doing with cheap circuits to
save a few pence, sometimes on cars costing 100k.
Andy
Owain
> I purchased a string of 10 Leds powered by 2 AA batteries connected in
> series giving 3 volts or thereabouts presumably.
> I was a bit sceptical about the life of the batteries so I left them on
> 24 hrs to check, I was surprised that they lasted over a month which
> makes them very useful as party lights in a damp conservatory, let's say
> running them for 4hrs a day which should make them last for 6 months
> perhaps.
I was thinking of getting some cheap battery LED Xmas lights but was
worried about battery consumption, if they will run for a month
continuously (on Tesco Value batteries?) that means I can stick them
up somewhere inacessible on 1st Dec and leave them on.
Owain
Steve Walker
Yes, I'm fed up of having a string of red squares or circles across my
vision as I look from one side to the other behind an LED lit car! The red
man on newer pedestrian crossings can have the same effect.
SteveW
Tim W
wibbled on Sunday 22 November 2009 20:47
>
> Yes, I'm fed up of having a string of red squares or circles across my
> vision as I look from one side to the other behind an LED lit car! The red
> man on newer pedestrian crossings can have the same effect.
>
> SteveW
There's simply no excuse for it. I was messing around with AVR
microprocessors and RGB LEDs, doing PWM on each element with a fixed cycle
period and variable mark/space. No problems running in the many kHz or even
10's of kHz.
Now, if for some reason this is problematic over metres of rough car wiring
looms, then the answer (if they want to be clever) is to build the lamp
controllers fairly local to the lamp clusters and slick them on one of the
control busses. Doesn't have to be one per lamp, could be 2 or 4 for
front/back or corners, plus another set for dash and interior.
I assumed they did something like this anyway to cut down on the number of
heavy copper conductors running everywhere, but I haven't looked hard
enough at my car to inspect the wiring looms to the lights.
If that is undesireable for them, (ie they are cheap or want to be simple)
then they would be better sticking with simple bulbs (which could be LED
bulbs in the same format with the same drive).
--
Tim Watts
This space intentionally left blank...
Steve Walker
I must admit that I thought that as more and more cars use canbus the lamp
controllers would all be local to the lamps. As you say, this reduces the
weight of copper that is needed.
As for the the frequency, indeed, there is no excuse for using such a low
rate.
SteveW
Calvin Sambrook
news:7msk37F...@mid.individual.net...
>series giving 3 volts or thereabouts presumably.
> I was a bit sceptical about the life of the batteries so I left them on 24
> hrs to check, I was surprised that they lasted over a month which makes
> them very useful as party lights in a damp conservatory, let's say running
> them for 4hrs a day which should make them last for 6 months perhaps.
Hang on a minute, many LEDs won't turn on at 3v as that's quite a low Vf.
Not only that but the normal arrangement for multiple LEDs is to put them in
series chains. You could put them in parallel but there are issues. I
suspect then that the 3V from your batteries is steped up to something
rather higher.
LEDs require a current source rather than a voltage and there are some nice
little ICs available which do all of the step up and current control in one
package, you may well have one of these in the lights you've bought. Have a
look near the batteries, if they're cheapo it may be a small black blob
rather than a chip as such.
> I got to thinking about dimming them, a series resistor would surely do
> that, but it would reduce the battery life by warming up the resistor.
If the lights use an IC to do step up and control then no, a resistor won't
work, or at least not in the way you think.
Even for simple resistor in series with LED circuits you wouldn't reduce the
battery life by increasing the resistor value. You would waste power of
course by heating the resistor but the overall current draw would be less so
the battery would last longer.
> Now you can dim filament bulbs by using an astable multivibrator and
> varying the mark to space ratio, relying on the chopping frequency and the
> time constant of the filament to provide a non flickering and dimmable
> light.
Again anything like this will screw up an IC controller, if that's what
you've got.
> Doing that to an led would cause flickering of the light but would the
> relativly slow response of the eye smooth out the flicker? as in film
> movies which I think have to be in excess of 25 fps in order to fool the
> eye.
Movies are 24Hz frame rate *but* they are double or treble shuttered to
avoid flicker. 24Hz is objectionable and unwatchable, 48/50Hz is right on
the limit and anything you'll see in a UK cinema will reach your eye at
72Hz.
Adam Aglionby
> "Donwill" <Donwill.see...@invalid.invalid> wrote in message
>
> news:7msk37F...@mid.individual.net...
>
> >I purchased a string of 10 Leds powered by 2 AA batteries connected in
> >series giving 3 volts or thereabouts presumably.
> > I was a bit sceptical about the life of the batteries so I left them on 24
> > hrs to check, I was surprised that they lasted over a month which makes
> > them very useful as party lights in a damp conservatory, let's say running
> > them for 4hrs a day which should make them last for 6 months perhaps.
>
> Hang on a minute, many LEDs won't turn on at 3v as that's quite a low Vf.
> Not only that but the normal arrangement for multiple LEDs is to put them in
> series chains. You could put them in parallel but there are issues. I
> suspect then that the 3V from your batteries is steped up to something
> rather higher.
Was thinking that but presume OP has red, green and amber chains,
red ,amber and green LEDs will run off sub 3V, blue and white need 3V+
to light and typically have 3 AA batteries.
B&M Homestores have a good range of both mains and battery operated
LED sets this year.
Cheers
Adam
Donwill
> "Donwill" <Donwill...@invalid.invalid> wrote in message
> news:7msk37F...@mid.individual.net...
>> I purchased a string of 10 Leds powered by 2 AA batteries connected
>> in series giving 3 volts or thereabouts presumably.
>> I was a bit sceptical about the life of the batteries so I left them
>> on 24 hrs to check, I was surprised that they lasted over a month
>> which makes them very useful as party lights in a damp conservatory,
>> let's say running them for 4hrs a day which should make them last for
>> 6 months perhaps.
>
> Hang on a minute, many LEDs won't turn on at 3v as that's quite a low
> Vf. Not only that but the normal arrangement for multiple LEDs is to
> put them in series chains. You could put them in parallel but there
> are issues. I suspect then that the 3V from your batteries is steped
> up to something rather higher.
>
> LEDs require a current source rather than a voltage and there are some
> nice little ICs available which do all of the step up and current
> control in one package, you may well have one of these in the lights
> you've bought. Have a look near the batteries, if they're cheapo it
> may be a small black blob rather than a chip as such.
after your email for a black blob or any indication of some kind of
electronic gizmo that might control current or whatever, I am pretty
sure there is nothing there. the leds have transparent plastic housings
and I can see nothing in the housings that might indicate that they have
anything significant in there either.
>
>
>> I got to thinking about dimming them, a series resistor would surely
>> do that, but it would reduce the battery life by warming up the
>> resistor.
>
> If the lights use an IC to do step up and control then no, a resistor
> won't work, or at least not in the way you think.
> Even for simple resistor in series with LED circuits you wouldn't
> reduce the battery life by increasing the resistor value. You would
> waste power of course by heating the resistor but the overall current
> draw would be less so the battery would last longer.
>
>> Now you can dim filament bulbs by using an astable multivibrator and
>> varying the mark to space ratio, relying on the chopping frequency
>> and the time constant of the filament to provide a non flickering and
>> dimmable light.
>
> Again anything like this will screw up an IC controller, if that's
> what you've got.
holder which includes a switch, no sign of a "black blob" there either.
The possible explanation that occured to me is that they have a
constant current diode built into the leds during the manufacturing
process and is visually quite undetectable.
>
>
>> Doing that to an led would cause flickering of the light but would
>> the relativly slow response of the eye smooth out the flicker? as in
>> film movies which I think have to be in excess of 25 fps in order to
>> fool the eye.
>
> Movies are 24Hz frame rate *but* they are double or treble shuttered
> to avoid flicker. 24Hz is objectionable and unwatchable, 48/50Hz is
> right on the limit and anything you'll see in a UK cinema will reach
> your eye at 72Hz.
to 1KHz at least.
>
>> In the interests of battery life, are there any dimmers of this type
>> available for leds?
>
discernable difference between them is that the 20 string has 3 AA
batteries in series.
I eventually cut off the battery housings and connected the two strings
in parallell powered by a Nokia mains charger ACP-7X which were being
sold off cheaply, if I remember correctly for 99p, the charger got a
little warm after 10mins use so I inserted a 2ohm power resistor in
series which reduced the current sufficiently to keep the charger
temperature within bounds. The subsequent light output was reduced
obviously but still adequate for my purposes.
This was just an experiment as I did not want to introduce mains
voltages to the still drying out conservatory (damp).
Thanks
Don
Donwill
http://www.opensourcepartners.nl/~costar/leddimmer/
which might be interesting to play with.
Cheers
Don
Calvin Sambrook
I'm still struggling to imagine how these are arranged. If they are in
parallel then each LED will have a wire going to it so that's 10 wires
running along the "string" plus the return which can be common which makes
11 in all. Each LED will require a current limiting resistance of some
sort. They will not share a limiting resistor as a mis-match between Vf of
individual LEDs leads to runaway conditions and dead LEDs so there will be
10 resistors. This is however a poor way to design battery powered LED
lights as If will vary significantly with battery terminal voltage, bear in
mind that a fully charged AA cell may be anywhere between 1.2V and 1.5V
depending on its chemistry.
It's just never done this way, in fact the only case where I've seen LEDs
controlled with a resistance commercially is in keyring lights where the
relatively high internal resistance of two button cells is relied on to
limit the current through a single LED. Your chain simply can't be using
the internal resistance of AA batteries as that can be very low in some
cases. In fact as a fun experiment try fitting NiCd or NiMh cells, either
it won't light because they have a lower V or the LEDs will pop because they
have a very low R.
What voltage is the mains charger? If you have access to a multimeter why
not measure the current.
Donwill
conductors in it; each conductor is connected to a leg of the 1st led
and then carries on to the next led, so in effect they are in parallel.
I found the invoice, and have a ref to the advert on ebay, you can see
on the pic how they are wired.
http://cgi.ebay.co.uk/10-LED-BATTERY-OPERATED-FAIRY-LIGHTS-S-Bright-White_W0QQitemZ260510075261QQcmdZViewItemQQptZUK_HomeGarden_Lighting_Lamps_Lighting_SM?hash=item3ca79c497d
I tried using my own camera but it wouldn't focus closely enough to
show the detail of the led connection.
I think I did at the time, but they are disconnected and back on the
battery packs now. I think it was (from memory) approx 350 mA (30 leds)
and the voltage was just over 3volts. Power supply rated at 3.7 Volts,
355mA
>
>
>
Cheers
Don
Clint Sharp
<csam...@bigfoot.com> writes
>I'm still struggling to imagine how these are arranged. If they are in
>parallel then each LED will have a wire going to it so that's 10 wires
>running along the "string" plus the return which can be common which
>makes 11 in all.
Think simple, the guys that make these things just use one series
resistor for all the LEDs, it's not good practice but it does work after
a fashion.
> Each LED will require a current limiting resistance of some sort.
If you want to do it right, yes they do. If you want to sell the lights
for a quid in the local pound shop (where I got mine) then they don't.
>They will not share a limiting resistor as a mis-match between Vf of
>individual LEDs leads to runaway conditions and dead LEDs so there will
>be 10 resistors.
In practice, I bet the mismatch between LEDs of the same batch is tiny.
>It's just never done this way,
It is. As you say, it's not the right way but it is done.
--
Clint Sharp
Calvin Sambrook
news:1yUdRhB9...@clintsmc.demon.co.uk...
Uk, I must remember to get out into the real world occasionally (apparently
the Real World is where the pizza delivery man comes from). I fear you are
right having seen the ebay item referred to.
Nasty but cheap.
mick
Yeah - I saw that one too. I decided that
a) it was probably a bit of overkill (you don't really need 0-100%).
b) it might be difficult (if not impossible) to get working from 3v.
I also considered using a PIC chip as those will work down to 2v. It
would be possible to use software PWM to drive a LED output MOSFET and an
analogue input from a "brightness" control. The problem is efficiency -
it probably isn't very... ;-) One of the little 8-leg chips like 12F683
would be the animal. This approach has one advantage over the others -
you can make the brightness control linear (to all intents and purposes),
no matter how the LEDs behave. You can also do silly things. :-)
Clint Sharp
<not....@invalid.invalid> writes
>I also considered using a PIC chip as those will work down to 2v. It
>would be possible to use software PWM to drive a LED output MOSFET and an
>analogue input from a "brightness" control. The problem is efficiency -
>it probably isn't very... ;-) One of the little 8-leg chips like 12F683
>would be the animal.
up and control with a pot. I reckon you could buy the chip and a capable
transistor cheaper than the equivalent non micro components needed to do
PWM.
--
Clint Sharp
Clint Sharp
<csam...@bigfoot.com> writes
>
>Uk, I must remember to get out into the real world occasionally
>(apparently the Real World is where the pizza delivery man comes from).
>I fear you are right having seen the ebay item referred to.
Oh I'm right, I bought a few sets because I can't buy LEDs that cheap.
>
>Nasty but cheap.
>
Definitely.
--
Clint Sharp
mick
<snip>
> Why use software PWM when that chip has it in hardware? Trivial to set
> up and control with a pot. I reckon you could buy the chip and a capable
> transistor cheaper than the equivalent non micro components needed to do
> PWM.
Oh yeah... so it has! I should have checked the spec sheet first,
shouldn't I? :-)
I might have a go at building this just for fun!
Clint Sharp
<not....@invalid.invalid> writes
>On Wed, 25 Nov 2009 22:19:02 +0000, Clint Sharp wrote:
>
><snip>
>> Why use software PWM when that chip has it in hardware? Trivial to set
>> up and control with a pot. I reckon you could buy the chip and a capable
>> transistor cheaper than the equivalent non micro components needed to do
>> PWM.
>
>
>Oh yeah... so it has! I should have checked the spec sheet first,
>shouldn't I? :-)
>
>I might have a go at building this just for fun!
>
Using the internal clock and an external transistor (BC639, first one I
found) it's very simple to code. I reckon the cost of parts is well
under 2 quid and I built it into the battery holder.
--
Clint Sharp
tahrey
That's basically the way most LEDs are dimmed in the first place. And
generally unless you're extremely sensitive, flickering at mains rate (which,
through a bridge rectifier, is essentially 100Hz, thus equal to all but the
most excessively high-refresh CRT monitors of old) should be imperceptible
when the diodes are stationary or only moving slowly relative to the eye. I
was in Homebase earlier looking at some light fittings and only realised that
one stand was displaying a mix of halogen and LED when I went to take a
picture with my phone and saw some of the lights strobing very gently on the
screen. Having been regularly annoyed by low-refresh CRTs back in the day, I
tried to determine whether there was any flicker visible to direct viewing,
but couldn't make any out even with the corner of my eye.
So if you were to use a 555 or other simple vibrator, so long as you tuned it
to operate at least somewhere into three figures that would be more than
enough to exclude flicker. If it's not visible with high brightness picture
tubes of 15 inches diagonal or more, it won't be visible with small, dim LEDs.
My phone itself has an OLED screen which probably refreshes somewhere around
120Hz (it's certainly not 60Hz) and the only evidence of flicker is if I wave
it around rapidly in pitch darkness. Most of the time you completely forget
it's not a regular LCD with a steady backlight.
I would question why you want to do this, though. I ran similar sets of lights
over christmas, and found them neither to be too bright for comfort, nor to
have such short battery lives or high voltage demands that running them off
"spare" batteries (non-rechargeables that had run too low to work in at least
one other more demanding device; freshly topped-off rechargeables would have
run a good bit longer) became an annoying performance of repeatedly switching
them out. Are they really too intense, or is changing the batteries every 3~4
weeks (which for christmas lights is essentially once a year) that much of a
hardship that building a dimming circuit is worth the hassle?
FWIW, if the problem is that they produce too intensely focussed little points
of light, I found that with a bargain bucket chain of multicoloured diodes,
which I think were initially supposed to come with star-shaped diffusers on
the end but turned out to lack them. A bit of pocket-money modification
turning them into a lantern string, by buying a pack of white plastic party
cups from Poundland, cutting small holes in the bottom of each cup and poking
a diode through each, proved to have a rather pleasing end result, with the
light being nicely diffused around the entire cone of the cup and giving the
whole string a softer, more traditional incandescent lantern type appearance.
Another mod that may be worth trying, if you have spare battery holders
sitting around, is to just run additional pairs of AAs in parallel, or hooking
the switch up to a pair of Cs or Ds instead. The overall bulk and weight of
the contraption still won't be particularly massive. In extremis a 3V mains
transformer, or a Poundland USB charger with a suitable dropper resistor (or
one charger wired to run two chains in series, though I'm not sure if they
produce much light with only 2.5v applied, my own tests suggest 2.6v is a bare
minimum; alternatively omitting the resistor and seeing if they stand up to
being overdriven to higher brightness, as they're probably underdriven by
design anyway) could be wired up to power it without any batteries, or even a
butchered cheapo solar-charging garden light or two for "free" non-mains juice.
--
for full context, visit https://www.homeownershub.com/uk-diy/10-leds-running-off-2-aa-batteries-597246-.htm
tabb...@gmail.com
NT