Some thoughts on LED status indicators

[Heemis]

So I've been building pedals for about a year and a half now.  I have done my share of kits, my own layouts, modded various circuits, etc  But I hadn't paid much attention to current draw until recently.

I finally replaced the fuse in my DMM and decided to check the current draw of the pedals I'd built.  They seemed to fall into the well accepted ranges, but I realized that in some circuits, the LED status indicator can be drawing more than 10 times more current than the circuit itself!  I'm sure many people here are aware of this, but I was quite shocked.  I started to test different current limiting resistors, seeing if I could strike a good balance between brightness and power consumption.

I have been a very conscientious energy user for a long time, so this definitely appeals to my "greener" instincts.  I've since done away with status indicators on pedals that are quite obviously ON, and I have found that using a 22k resistor in place of the often 1k-4k7 resistors people use for LEDs is usually more than enough to light an LED on a dark stage.

Just as an example, I recently built a Trotsky OD, and used a 22k limiting resistor on the LED.  At max gain, the pedal draws less than .5mA of current, a far cry from the nearly 5 mA it would have drawn using a 1k resistor.  I would be hard pressed to tell the difference on a poorly lit stage.  (In terms of standard alkaline battery life alone, assuming 550 mA hours of capacity, this is the difference between over 1000 hours at .5 mA, and right around 100 hours at 5mA)

Of course, current draw varies greatly from circuit to circuit, and from LED to LED.  But I've found that you can go a long way to reducing your current usage in simple transistor based distortions and fuzz circuits with plain red LEDs by simply trying a larger current limiting resistor in your circuit.

Here's a fantastic resource just to ballpark some LED current draw scenarios courtesy Jack Orman:  http://www.muzique.com/schem/led.htm. 

The best way however is to be aware of current draw in your circuit, use only the current that you need to know the pedal is ON, and do your part to reduce your energy consumption!

And don't forget, reducing current consumption not only extends the life of your batteries, it also consumes less energy from the wall when using an adaptor, which is good for everyone!

[ayayay!]

And don't forget, reducing current consumption not only extends the life of your batteries, it also consumes less energy from the wall when using an adaptor, which is good for everyone!

OK, innocent question here, but is that really true?  What I mean is, once a transformer is done converting from AC to DC, that's all there is to it, right?  The conversion itself has a byproduct of producing heat, which can be easily observed when there's nothing even plugged into the DC jack.  I don't think it's going to make a noticeable difference unless it's just unplugged from the wall. 

Let's say a transformer converts 110-120 volts AC to 9.6 volts DC, with a maximum output of 300mA.  That 300mA is always available, whether used or not, right?  So isn't the real loss on the AC side with all that current being wicked away as heat?  Not trying to be a pain, it just seems like a good question. 

[Captainobvious99]

I wanst aware it made such a huge difference on battery life. I think I'll play around with some resistor values and see what combo's work well  without draining unecessary battery life.
Good post.

[jefe]

OK, innocent question here, but is that really true?  What I mean is, once a transformer is done converting from AC to DC, that's all there is to it, right?  The conversion itself has a byproduct of producing heat, which can be easily observed when there's nothing even plugged into the DC jack.  I don't think it's going to make a noticeable difference unless it's just unplugged from the wall. 

Let's say a transformer converts 110-120 volts AC to 9.6 volts DC, with a maximum output of 300mA.  That 300mA is always available, whether used or not, right?  So isn't the real loss on the AC side with all that current being wicked away as heat?  Not trying to be a pain, it just seems like a good question. 

I think you bring up a good point. I'm not sure if you're correct, but it sounds right. 

"Green" reasons aside, I just don't like my LEDs to be too bright. It annoys the hell out of me when I bend down to twiddle a knob, only to be blinded by an ultra-bright LED. The bright lights look pretty, until you put them to practical use.

[Mark Hammer]

I've been here so long that my memory of "we just discussed this recently" may be drawn from another century, but we HAVE discussed the overall issue of status LEDs in past.  Whether that is findable with the search feature may be another matter, but we have discussed it.

A quick synopsis of what was discussed might consist of the following:

• Where possible, use a superbright LED so that current draw can be reduced by means of a more efficient LED
• Where possible, situate the status LED so as to increase visibility; greater visibility reduces the requirement to make it brighter; that can mean keeping it out of the way of knobs
• Where possible, increase visual contrast so as to make the LED more visible; that can include strategic use of LED colour (if I catch a blue one of the corner of my eye then my flanger is on, but green means my compressor), strategic use of chassis colour (LEDS show up better against dark backgronds) and strategic use of bezel colour (dim LEDs show up better against a black bezel than a snazzy chrome one)
• Where possible, reduce current draw by means of a current-limiting resistor as much as you can stand
• Where possible, use intermittent indication, such as blinking LEDs rather than always-on

[oskar]

Let's say a transformer converts 110-120 volts AC to 9.6 volts DC, with a maximum output of 300mA.  That 300mA is always available, whether used or not, right?  So isn't the real loss on the AC side with all that current being wicked away as heat?  Not trying to be a pain, it just seems like a good question. 

Heemis is right.
There is a minimum power drawn from a regulator. If I put a hand on the charger of my cellphone it's warm even with nothing connected so I allways disconnect it. That is the power allways lost that you're thinking of.
But this is only a part of the total delivered power.

I'm now watching three LED's. One power indicator on the computer and one at the monitor and one blinking at an unused monitor...
Ok. I just unplugged the unused computer/monitor      ,thank's Heemis...

Most LED's are run off 5V. If everyone on the planet gets one LED i calculate like this:

6*10⁹persons*5V*10mA=300MW
That is one third of what the reactor that caused the disaster in Chernobyl could put out as a maximum. I just ran out and turned off the TV  noticing the router showing off with 6 more LED's...

[frequencycentral]

Most LED's are run off 5V. If everyone on the planet gets one LED i calculate like this:

6*10⁹persons*5V*10mA=300MW
That is one third of what the reactor that caused the disaster in Chernobyl could put out as a maximum. I just ran out and turned off the TV  noticing the router showing off with 6 more LED's...

OK - you've got me so scared that I'm now going to have to turn off my computer.

[Heemis]

I suppose I sort of already knew that adapters draw power whenever they are plugged in... I do use a master on/off switch on a power conditioner that I plug all my electronics into, and I shut it off when I'm asleep, and when I go to work.

I guess the question still stands, do adapters draw MORE power when the device they're connected to is in use?  Maybe someone has a definitive answer?

Thanks for the follow up Mark.  I guess the topic would be better situated in a pedal building FAQ or wiki... although I can't remember having seen such an article.

Oskar, since having this LED power consumption revelation I've started noticing the use of unnecessary LEDs everywhere!!  Just imagine if each one of them was tuned down to it's lowest possible effective brightness...

[oskar]

I guess the question still stands, do adapters draw MORE power when the device they're connected to is in use?  Maybe someone has a definitive answer?

Whithout a doubt, YES!
The fundamental laws of thermodynamics still stands...

Oskar, since having this LED power consumption revelation I've started noticing the use of unnecessary LEDs everywhere!!  Just imagine if each one of them was tuned down to it's lowest possible effective brightness...

They probably are running really low actually. Except the status LED on my screen.
Many LED's are pulsed so if they are driven by a microprocessor the processor turn them each on and off in turn... But my math gives a general idea of the problems the modern civilisation is up against. I don't want to think about the consecuences of all those Marshall stacks out there!

[Heemis]

Well, that settles that!  Thanks Oskar!

It is truly mind blowing when you stop to think about how much energy is used around the world all the time.  I feel bad every single time I turn on my tube amp.  I guess the real problem isn't using the power, it's just using more than you need.

It's good to know that we, the diy stompbox community can make a difference in our small way.

Soon enough I've got to start work on building an 8 AA rechargeable battery pack, and a solar panel to charge them... i'm only half kidding.

[ayayay!]

1st, Heemis I am so totally sorry for hijacking your thread!  

Quote from: ayayay! on Today at 02:34:26 PM
Let's say a transformer converts 110-120 volts AC to 9.6 volts DC, with a maximum output of 300mA.  That 300mA is always available, whether used or not, right?  So isn't the real loss on the AC side with all that current being wicked away as heat?  Not trying to be a pain, it just seems like a good question.  

Heemis is right.
There is a minimum power drawn from a regulator. If I put a hand on the charger of my cellphone it's warm even with nothing connected so I allways disconnect it. That is the power allways lost that you're thinking of.
But this is only a part of the total delivered power.

I get that.  I really do.  But what I'm asking is this:  Is more energy being consumed beyond what has already been converted?  My gut says no.  Of course, the pedal itself does use that energy that it needs.  No arguing there.  But since the 300 mA in my example is always there, always ready to be used, always converted from AC via the transformer, is even more energy consumed by plugging a pedal into the other end?

My reasoning is, you plug in a pedal that uses 5mA.  Ok, so now you have 295 mA to spare.  You've now created a load.  And even though small, it completes a circuit where 300mA of available potential can be used.  So therefore wouldn't the transformer be the real cause of loss, not a pedal pulling juice?  

In other words, 5mA used + 295mA unused still equals 300mA worth of energy that has been converted, does it not?  Anyway you slice it, 10mA used plus 290mA unused, 100mA used plus 200mA unused, it doesn't matter:  300mA is the final product of the transformer and it is all either used in a circuit or lost as heat.  Either way, it's not consuming 300mA PLUS the extra power of the pedal, see what I mean?

My pea-brain apologizes if I'm confusing everyone.  I'm not trying to argue, I just want to understand this.  

[runmikeyrun]

here's another thought- blinking LEDs... it's off 1/2 the time so it draws 1/2 the current!

[oskar]

My reasoning is, you plug in a pedal that uses 5mA.  Ok, so now you have 295 mA to spare.  You've now created a load.  And even though small, it completes a circuit where 300mA of available potential can be used.  So therefore wouldn't the transformer be the real cause of loss, not a pedal pulling juice?  

There is a lot to keep track on here so there is every reason to get confused.
I have marked in red the crucial point where your reasoning fails. The available potential is not consumed. Only a fraction of energy (how big this fraction is depends on how good the power regulator is in this sense, I really don't know) is used to make the regulated DC vailable for your listening pleassure.

In other words, 5mA used + 295mA unused still equals 300mA worth of energy that has been converted, does it not?  Anyway you slice it, 10mA used plus 290mA unused, 100mA used plus 200mA unused, it doesn't matter:  300mA is the final product of the transformer and it is all either used in a circuit or lost as heat.  Either way, it's not consuming 300mA PLUS the extra power of the pedal, see what I mean?

In other other words 5mA + regulator waste (25%*300mA=75mA)=5mA+75mA=80mA   ...Just as an example

If you have just an AC/AC transformer connected and the secondary side is not closed I don't think it draws any power at all.

[Heemis]

ayayay, no need to apologize at all!  It's totally appropriate to the content of the post.  I am actually very interested in this as well, and I'm glad oskar is shedding some light.  I've been searching the all-knowning internet for the past 20 minutes or so on the subject, and all I can seem to find is that adapters do consume SOME amount of power whenever they are plugged in.

[drk]

the 300ma is just a rating, the transformer isnt providing that amount.
it just means it can safely provide that, and not more.

[oskar]

...and all I can seem to find is that adapters do consume SOME amount of power whenever they are plugged in.

I'm going to forward this question to an echology forum I'm part of.

The easiest way to find out, I think, would be to measure it. You can't really trust the figures because you need to know what rating to look for and things like standby effect and a self consumtion in a power regulator isn't a priority. Maximum rating is.
High up on my list of wanted tech stuff is a power meter. They're not expensive and you can find out instantly what your TV/stereo is consuming when you think it's off.

[cab42]

Reading this thread reminded of a post by R.G. on how to calculate the size of current limiting resistor. A great read!

http://www.diystompboxes.com/smfforum/index.php?topic=30168.msg205430#msg205430

Regards

Carsten

[flo]

and all I can seem to find is that adapters do consume SOME amount of power whenever they are plugged in.

This is actually quite easy to verify:
- Plug the adapter into the wall socket.
- Do NOT connect any devices to the adapter.
- Wait a few minutes.
- Put your hand on the adapter and notice how warm it has become.

The heat is an indication of the energy being consumed and wasted by the adapter without it actually doing anything useful (powering equipment).
Now image all the adapters in the world being plugged into the wall sockets, producing heat without doing anything useful. All wasting energy and contributing (quite literally) to global warming...
I'm unplugging everything that I don't actually use either directly after use or whenever I leave my home for a while or when I go to sleep.

[ayayay!]

The available potential is not consumed.

Ok I get that, but that's still not what I'm getting at.  And I sincerely apologize to everyone for my hair-splitting. 

If you have just an AC/AC transformer connected and the secondary side is not closed I don't think it draws any power at all.

Agreed.  So is that what you're saying then?  That it's only going to expend what the load asks of it?  I can buy that.  It seems feasible.

Let's use a transformer now as a kind of "endless 9V battery."  The battery will only be expending the tiny load for the effect, say 5mA, but doesn't wear out because it has an infinite (time wise) supply of potential at the ready.  Follow me?  Now change it back to a transformer.  It still has this infinite supply of potential time wise, but now has a finite limit of potential current wise, which in my case is 300mA.

How was that defined?  By the characteristics dictated by the transformer.  The transfomer dictated it.  Signed, sealed, delivered, it's done.  The energy has been spent by the transformation, and once a load is place on it, no matter how small, it's always going to be wanting to give 300mA, is it not?  The only thing stopping it is the resistance of the load.  It's still got 300 mA worth of pressure/potential/current as an effect of the transformer once a load has been placed in the path right?  I mean, hasn't the mantra in this forum always been, "A pedal will only take from a power supply what it needs to operate"? 

I guess what I'm saying is when you use a power supply to transform your voltage and current, you've already made the omelet and broken the eggs, so what happens beyond that isn't really going to save any more energy than what's already been converted and waiting to be used is it?  If you say so then I won't argue with it, but I just want to understand it.  Thanks for your help with this Oskar!!!   

[R.G.]

Ok, let's get down to the technical details.

Power Adapters:
All power adapters use some power when plugged in. In almost all cases this is a few percent of the full-load power they can provide. There are two types of these adapters, those being (a) 50 or 60-Hz transformer based and (b) switching power supplies. The power line frequency units (a) may run as much as 5% of full load power or as little as less than 1%.

On a purely engineering level, this is amazing. Very few electronic devices and no mechanical devices convert as much as 95% of their input energy into output. The switching versions (b) are even better. They can be designed to use much less than 1% of the full load power when under no load. In its quest for perfect greenness, the state of California has now made the under-5% version illegal to sell, demanding the switching version regardless of cost and regardless of the increased monetary price, higher EMI emissions, higher embedded energy, and rare/toxic materials used in making switching power supplies to replace iron and copper. But I do have to admit, calling it "Vampire Power" is a cool political slogan, isn't it?

Power used:
An adapter is marked with the maximum power it CAN put out, not what it uses. All adapters have a technology that is (as noted above) approximately energy in = energy out. If the adapter is unloaded, no, it does not sit there and eat up its full rating internally. It puts out only what it being used plus the small fraction used to start it up and keep it going, as noted above.

Power saved:
Saving 300MW sounds like a great goal. But to put it in perspective, sunlight provdes 1KW/m². Then 1000m² gets 1MW, and 300km² provides the same power. It may well be easier to produce that much more energy. Or to save it somewhere else.

This reminds me of the newspaper reporter who asked Clyde Barrow why he robbed banks. Clyde replied "Because that's where the money is." If you're trying to save energy, it's best to figure out where the most energy is going and make a small reduction in that, rather than trying to eliminate tiny ones. And in fact, there is the potential to save much, much more than you might attacking the tiny ones.