Introduction: How Green Is My Green Electronics ? Now With Improved Threshold Detection !

Picture of How Green Is My Green Electronics ? Now With Improved Threshold Detection !

Are electronic devices really in a very low power mode when on stand-by ?
Also, how much energy am I wasting for powering devices when not in use ?

I wanted to check it out and decided to build a device capable to detect stand-by mode of my electronic devices and start metering energy used. All this had to be done automatically without my intervention. Metering would start upon entering stand-by and stopped upon exiting.
To do so I needed an energy meter and a current gauge to monitor the current of mains supplied devices and start/stop metering.
For the meter I first looked for silicon, of course. Energy metering is a hot issue with a lot of chip makers and many of them supply cheap solutions.
The project was proceeding when recently I was lucky enough to find two electromechanical meters at a local special trash collecting center (electrical, white goods, furniture).
Actually there should be a plenty of these scrap meters available here as the local electric company is replacing these meters with remotely controlled electronic meters.
I took them along with two VCRs and a printer. The first meter I opened and dismantled to satisfy my inner primary need. The second meter I decided to use in place of the silicon-based one; also, the ready made electromechanical meter solved the calibration issue.
This PopSci contest made me hurry and change priorities in my to-do-list, so here is my design.
Schematic V0.2 is an improved version of the electronic control box over the previous one. I added a potentiometer to set the hysteresis level. This helps discriminate power on vs. stand-by for noisy power supplies like some switchers are. This also helps get firmer metering on/off states.
The schematic shows in red the differences with respect to previuos version.

Step 1: Caution, Safety First !

Picture of Caution, Safety First !

Before starting, you must be absolutely aware that this thing is powered from the mains and
as such it could kill you, cause damage or injuries. If you are not really skilled at mains
powered electronics and related safety building practice and are not well aware of the risk related, you are suggested to have a friend help you with this project.
Also, as a general rule, when you are working on dangerous things always have someone next to you instructed on what to do if something goes unexpectedly.
Most parts of the circuit should not be considered safe to touch when the circuit is powered on.
Keep low voltage and high voltage wiring as separate as possible. The relay is the point where the two worlds are closer. Choose a good relay and have the wires soldered firmly. Tape well and possibly use heat-shrink tube.
These notes are not just to scare or bother anyone, but I absolutely want that fun does not turn
into grief.

Step 2: How It Works. Electromechanical Meter

Picture of How It Works. Electromechanical Meter

Electromechanical meters are described very clearly here.
The key point: metering is based on the product of two electrical entities, current I and
voltage V; power is the product of these two entities, V and I. Energy is calculated integrating
over time (that is adding together time after time) the V*I products. It is energy what we are
paying for.
Within electromechanical meters V and I feed two coils: the voltage coil (which is in parallel to
the line) requiring low power and a current coil (in series with the line) made of thick copper wire.
Metering can be stopped or started interrupting the connection to the voltage coil.

Step 3: How It Works. the Current Monitor

Picture of How It Works. the Current Monitor

The current required by the electronic devices under test is monitored through a current transformer.
I made it out of a regular wall adapter: I removed the low voltage secondary winding and replaced it with 4 turn of paired 1.5 square mm insulated wire. Current flowing through the new winding produces a voltage across the untouched original 110Vac side of the transformer. The higher the current, the higher the voltage.
The untouched 110Vac primary is then connected to a filter stage, a variable gain amplifier
a full-wave rectifier, a peak detector and a threshold detector feeding a transistor and a low
power relay. The contacts of the relay are in series with the voltage coil of the meter.
The gain of the amplifier stage is regulated through a potentiometer to set the threshold stand-by / operational.
You can find the detailed schematic down here.
All the parts are pretty common and most of them can be salvaged from other electronic devices.
Almost all the electronic components I took from a VCR and an automatic IR night light.

Step 4: Putting It All Together

Picture of Putting It All Together

I had a piece of wood cut to measure to make a stand the size of 25x25x8 cm.
Attached to it the meter, an avory-white plastic box containig the input and output cabling and the
current transformer. Finally attached a gray plastic box with all the electronics. The relay I put
close the wiring points of the meter. This also adds to safety.
The wiring runs at the back of the stand. I dremel-led the paths for the wires in the wood and kept the wires in place with duct tape. Next step will be to add a 3-4 mm thick piece of plywood to cover everything.
Now, check the wiring again, make sure you did not connect in parallel anything supposed to be in series, this applies expecially to the meter.
Rotate both gain and hysteresis potentiometers counterclockwise (minimum resistance, i.e. minimum gain and wider hysteresis window).
Connect the electronics you want to test. Plug the meter.

1.) Turn off your electronics. Rotate the hysteresis potentiometer clockwise until the relay energizes (and the LED turns on) and the meter wheel starts rotating. if nothing happens rotate the hysteresis potentiometer clockwise until the relay energizes.
2.) Turn your electronics on and the relay should de-energize. If nothing happens, turn the gain potentiometer a little further clockwise (higher gain).

Repeat the 2 steps above again to trim.

Should you find difficult or impossible to set the threshold, likely the stand-by mode current is close to the operating mode. This means your equipment consumes almost the same regardless powered on or in stand-by.
Once you know the energy (in Watts per hour) used by your equipment, you may also want to know the average power dissipated by your electronic device. This can be done if time is counted along with the energy. That is, if 10 Wh were metered in 100 hours, an average of 10/100 = 0.1W is the power dissipated by the equipment. For this purpouse a battery operated wall clock timepiece can be connected at the points +/-1.5V in the schematic.
The timepiece will be powered (and then advance) only when the relay is on.

Step 5: Final Notes

Picture of Final Notes

If you just want to have an idea of the stand-by current with relation to operational power, you may just want to build the current transformer and connect the filtering resistor and capacitor. A multimeter at the RC filter gives readings in the range of tens of mVolt to a few Volt. Values depend on the transformer used.

You will find that a number of electronic devices do not have a real stand-by mode. Rather they turn a red LED to green and respond to remote control commands, but they are fully powered on when on stand-by as well. This consumes a lot of energy and you can have the feel touching them: they are always warm (quite warm, sometimes !).

I have my home entertaining system connected to a switched outlet I switch on only when we are going to use it, otherwise my 5.1 system would be always hot.

I am not sure that this will cut bills and solve related problems, as shown in the drawing Michele made a few moments ago, but I am absolutely sure that resources we save today will be handy in the future to Michele and his brother.

Ciao a tutti


saadsms (author)2012-03-04

thank you

adam13013 (author)2010-07-07


Lee Wilkerson (author)2010-04-23

How much does it really matter anyway when our clothes dryers, toasters, cook-stoves, ovens, refrigerators, irons, blow dryers, and air conditioners all draw 1 KW or more (mostly more)?
Good instructable on building an AC current meter, though.

hot-fresh-rider (author)2010-04-23

green is a red herring. there is nothing green about electronics. I propose a title correction! How energy efficient are my electronics projects?

5Volt (author)2007-10-10

I understand, the device requires too much work compared to (possibly cheaper) digital devices on sale ! I would never make it either (again !).
It was a sort of divertissement.
The plugs here are very safe as it is practically impossible to come in contact with the live metallic part while plugging in. Also, the sockets in the wall require that all three contacts enter the socket at the same time thus preventing young experimenters from putting wrong things in the socket.
The female (right) can accept 16A larger holes and 10A (smaller holes) plugs. Ground is center and there's no polarity (Line and Neutral can be exchanged). We run on 50Hz while US and some other countries run on 60Hz.
As we run on 220Vac, for a given power requirement we use smaller cords (less Amps are required).
Hola !

Davvik (author)5Volt2008-02-01

That does seem a lot safer than our American outlets, Because like sometimes if you are plugging in an electronic device and your hand slips you will get a nasty shock.

gormly (author)Davvik2008-03-16

Davvik no offense, but you are seriously mistaken. It make look safer (and cooler) but really it is no different, it is almost impossible to shock yourself if your "hand slips". It is safe by design. I am a certified electrician and I have worked in electric work shops for 20 years and I have never, ever seen or heard of someone electrocuting themselves with improper use of an "American" style plug.

Bad Maxx (author)gormly2010-04-23

WOW! I beg to differ, no offense intended but:

"CPSC document number 524 Electrical Receptacle Outlets" "Electrical receptacle outlets in walls and floors may present shock and electrical fire hazards to consumers. The U.S. Consumer Product Safety Commission estimates that 3,900 injuries associated with electrical receptacle outlets are treated in hospital emergency rooms each year. Approximately a third of these injuries occur when young children insert metal objects, such as hair pins and keys, into the outlet, resulting in electric shock or burn injuries to the hand or finger. CPSC also estimates that electric receptacles are involved in 5,300 fires annually which claim 40 lives and injured 110 consumers........"

So if only 1/3 of the 3900 annual injuries received from electrical receptacle outlets are children, it is fairly safe to assume the remaining 2,601 shock receivers would indeed be adults using an outlet and through some type of mishap were indeed shocked, if not worse. 

 I know in my lifetime I have received two electrical shocks from "slipping" down to the metal prongs while plugging into an electrical outlet, and I know of other people who also have done so, I only mention this as none of us ever reported these incidents to anyone! This despite the first incident knocking me unconscious while plugging in a lamp while reaching behind the couch to do so.

hcold (author)gormly2008-03-30

Arr, when I plug in our CRT TV into a multi board sometimes I notice a bright white/blue flash under the plug. I have also noticed this while plugging in a light to a completely different multi board in a different room.

static (author)hcold2010-04-23

An arc is most common when unplugging a device that's turn on, but not unheard of when plugging the same in.

5Volt (author)hcold2008-08-18

Oops ! I notice your comment quite late and thanks to Derinsleep reply...
Sorry for overlooking.
Anyways, the blue flash you noticed is pretty common and is due to a very interesting (geek-ly speaking) physical law, the lenz' law where when an inductive circuit like those with motors or large transformers (like the ones in TVs) or some large light bulbs is connected or disconnected from power a large voltage is generated with the white/blue spike you saw.
Physically speaking, the magnetic field generated by the inductive circuit (the motor, the bulb, the transformer) opposes to changes when the circuit is opened or closed generating a reverse voltage such that the current associated to the voltage and the circuit will be such that the flux it creates opposes the change in flux that created it ( quoting wikipedia in part)
Hope this helped

Derin (author)hcold2008-07-10

arcing,not that important,I just kick the power bar and my TV works again!

Derin (author)gormly2008-08-02

aka NEMA

Davvik (author)gormly2008-03-16

I say American but I meant North American, I'm from Canada, and I've never really electrocuted myself, I've just shocked myself because I wasn't paying attention when plugging something in. and a lot of my outlets are broken and very unsafe, so it might just be because my house is old.

Derin (author)5Volt2008-08-02

Hmmm,they don't need the center pin since I can plug my laptop that has the other euro plug into the italy outlet. Italy is awesome,by the way.

5Volt (author)Derin2008-08-16

Ciao D., sorry for not replying earlier but I was on a trekking vacation and couldn't do any Internet stuff. Yes, live and neutral on Schuco plugs are the ones protruding out of the plug handle but plugging it into a regular Italian plug would leave the safety earth unconnected. Also, the diameter of Schuco pins is larger than the italian ones. Oh yes, Italy is awesome as many other countries around the world. Thank you ! BTW, I've just noticed that 'Italy' is not in the Instructbles spelling checker ! :-)

Derin (author)5Volt2008-08-17

That is true for sure,but I saw outlets that can accept both plugs with the earth always connected.

5Volt (author)5Volt2007-10-10

Oops! I meant fewer Amps.

hellcat26 (author)2010-04-23

 se ve interesante este aporte

mrmarshall1 (author)2009-07-04

all of this for a power meter? a hacked GFCI (ground fault circuit interrupter) outlet would give you better results. GFCI outlets work by measuring how much energy goes in and how much comes out, when there not the same it trips.

static (author)mrmarshall12010-04-23

A GFI doesn't actually measure power/energy, so I'm unsure how a hacked GFI could give better results.  A GFI monitors the current flowing through a circuits line ans neutral conductors. When that currents varies by a preset threshold the GFI assume current is flowing through a human to ground, and trips. That is not to say there aren't components that could be salvage from a GFI that could be used to construct a power meter, but the construction of the circuitry to measure current and voltage will end up very similar to how it has been done here.

5Volt (author)mrmarshall12009-07-07

I'm not sure that a GFCI actually measures anything and what your hack could be. Anyways, why don't you post an instructable on the hacked GFCI ?

mrmarshall1 (author)5Volt2009-07-12

im working on it all i have to do is design a circut.(my weak side) in the mean time if you have a broken one or just one laying around take it apart.

Visitor (author)2007-03-26
Interesting instructable. Where I live one can borrow a device similar to this "kill-a-watt" meter from the city energy department.

I measured the electricity consumption of my entertainment electronics in the state they are when not used.

  • Monitor (off) 0W
  • Computer (off) 3W (always provides electricity to rear panel USB ports, only keyboard and mouse were attached)
  • ADSL (off) 1W (the mechanical switch is between transformer and the device)
  • Stereo (stand-by) 5W

And also the rarely used bedroom VCR draws 3W when in stand-by.

These are all devices that are theoretically needed only for 8 hours max each day (assuming I spend 8h at work and 8h asleep).

During one year these devices would completely _waste_ as much electricity as a 90W incandescent light bulb does when left on for 1 month (likely more, since I don't need to use all of them for 8 hours every day). Luckily they are all connected with extension cords that are very easily accessible so I can unplug them when I don't use them without causing any decrease in the quality of my life.

Not that I consider quality of life a reason to waste electricity...
trebuchet03 (author)Visitor2007-03-26

Not that I consider quality of life a reason to waste electricity..

Exactly -- now think about it (maybe you have, but for others to see realize this).... Let's say there's one computer per person in the United States (theoretically, 300 million). Each will draw at least 3W (that's an assumption) - That's 900000 kilowatts. For one year, that's 7,776,000,000 Kilowatt hours!

For more perspective - that amount of energy is equivalent to 1,102,000,000 pounds of natural gas ASSUMING we can extract that energy with 100% efficiency (actual numbers are significantly lower). So it's like voting, you're small effort does count - especially if you tell someone else what effect it has :)

All of that so we can keep our computers plugged in and off. And yes, there's some large assumptions there - but even if you divided that in half - that's still a HUGE number. And my significant other laughs at me when I say I'd love to live off grid :P

And to finish off my mini rant... did you know about a third of America's engineers are retiring in three years (at least they're ready to). At the moment, the average engineer work load is something like 47.5 hours per week and rising every year. Of engineers surveyed, ~45% said elementary through high schools get a D or an F for prepping for engineering and prepping for engineering v. other carries. And staggering, 60% said D or F compared to other countries (which means any other country). Luckily the university scores were higher - but, it's still a problem that about half of those that begin in engineering washout typically due to unpreparedness.

Problem: Energy
Question: Who's going to work on this problem?

I dare you - ask a kinder gardener to draw a doctor... then a lawyer.... then ask, draw me an engineer. Here's a hint - one child in that class drew something for an engineer -- a person looking at a car with it's hood up but everyone could draw the doctor and the lawyer o.0

/rant (sorry, it's not directed at you - but energy just gets me fired up)

jufemaiz (author)trebuchet032010-04-22

The problem is actually beyond some of the issues (when we're talking about what's referred to as "phantom power") - the problem is really the low cost of energy versus the high quality of life enjoyed as a result of it.

While I would agree that there is a disconnect between people understanding their energy consumption (in terms of dollars and kWh) there's also a problem with the amount of utility people enjoy as a result of that standby power. They *do* enjoy the ability to turn equipment on by remotes, to come home to an HVACed house set at the temperature that they want, to run large energy-inefficient devices and appliances (look at the prevalence of large trucks in the US and other nations for general transport needs).

When people both have more information on what their using and how much its costing, along with more exposure to the prices of delivering the energy they wish to consume, they will be in a position to make informed decisions on their energy usage. We're a long way from that.

You're absolutely right about the disregard for engineering, but engineers themselves are also to share part of the blame. We need to ensure the community understands what we do and where they receive the benefits of our services. A big part of the problem is the lack of face-to-face time with the community engineers have. Doctors, Lawyers, Accountants etc all spend a lot of time interacting with the community, Engineers generally do not.

Finally, we need to shift people away from being proud of being innumerate and make it something like illiteracy - something that should not be championed.

5Volt (author)trebuchet032007-03-27

As we are approaching the end of the oil age (someone say we are already there) we must keep in mind that oil is a prime matter for a lot of special materials. Burning it into supercars or using it to keep monitors in stand-by may not look very smart in perspective. Energy gets me fired up too. Ciao

trebuchet03 (author)trebuchet032007-03-26

Darn, I forgot to include one link... EE Time's on the State of the Engineer

LinuxH4x0r (author)2007-09-29

Consider this. The site (google, except black) saved 225,654.349 Watt hours as of September 29 2007 just by being black. Black uses less power on the old school crts. And thats just one site changing it's color! Be Green! - Buy me an LCD ;-)

jufemaiz (author)LinuxH4x0r2010-04-22

The articles that Blackle site to back up their claims are old, especially in terms of the technologies available to date.

I wrote up a small article on Blackle and their claims when they first launched. Additionally, the owners of Blackle egreriously claimed (via emails that were forwarded globally) that Blackle was a Google creation and not an entrepreneurial venture using environmental claims as a cover.

End of the day the values that are being claimed are on experimental data from 10 years ago. These need to be rigorously checked for accuracy - as all science requires.

As noted below LCDs use more power to show black (even if only marginally). LCDs are continually backlit (a good portion of the energy goes here) and the RGB components darkened by applying a voltage across each crystal to be twisted to prevent the light being visible.

More interesting will be the energy savings when OLED based displays are widely available at cost competitive prices. Then dark screens really will have the ability to save energy (and money) - and be more efficient than CRTs into the bargain.

Derin (author)LinuxH4x0r2008-03-22

and uses more power on lcds

LinuxH4x0r (author)Derin2008-03-22

Actually it uses the same

Derin (author)LinuxH4x0r2008-03-22

hm a lcd needs power to darken while a crt uses more to brighten.

Azayles (author)Derin2010-04-22

Actually most of the power used by an LCD screen is for the back light (whether it's LED or CCFL). The power used to switch the state of the LCD panel itself is so small as to be negligible (it's in the range if micro amps), so for the most part, the power used is the same, regardless of whether black or white is displayed.
However, many modern monitors are utilising a technology which involves dynamically changing the brightness of the backlight depending on whether a dark scene or a light scene is being displayed. This it to give high brightness to light scenes, while still giving good contrast on dark scenes - an overall better gamma throughput.
This means that for these monitors, dark scenes ultimately use less power.

LinuxH4x0r (author)Derin2008-03-22

Yes, but in a desktop application it is being powered by a transformer that is always using the same amount of power. What you said is only true in battery powered devices like laptops.

Derin (author)LinuxH4x0r2008-09-01

then how does the power save mode work?

duane534 (author)Derin2009-01-12

There's a difference between darkening with the LCD and complete black. Think of the electronic method as the dark lines on an Etch-a-Sketch and the power-save as shaking it.

casey321b (author)duane5342009-02-21


LinuxH4x0r (author)Derin2008-09-01

Isn't that when its off? Its sort of like a car. When its not moving it still burns gas in idle.

duane534 (author)LinuxH4x0r2009-01-12

Transformers only step up / down current that is being drawn. It still varies.

Derin (author)LinuxH4x0r2008-05-18


merseyless (author)Derin2008-12-15

battle of the penguins! epic...

duane534 (author)Derin2009-01-12

True, but comparing a CRT displaying full-on white and an LCD displaying full-black is like comparing a hybrid Suburban SUV to street racing a Prius.

pharoah (author)2009-04-26

Somebody needs to change this title, it should be:
How green are my green electronics?

(Wonders why conjugating verbs in one's own language is so tough for people)

5Volt (author)pharoah2009-06-23

pharoah said: Wonders why conjugating verbs in one's own language is so tough for people It may happen when english is not one's own language. Didn't realize that ? Thank you, I cheer it that as a compliment ! Alessandro Genova - Italy

pharoah (author)5Volt2009-06-26

No, honestly I didn't realize you weren't a native speaker because the rest of your instructable is so well written. This has got to be one of the most common errors I hear my fellow Americans making (in 2000, President Bush remarked "Rarely is the question asked, is our children learning?"). Anyway, I'm sorry that I criticized you. Back when I was preparing for the SAT I saw errors everywhere :).

Punkguyta (author)2009-06-23

I would really like to do this, but I want to make a system that is monitored via my computer, or one of my old towers I could set up for collection of the data via serial or something. I know it's possible, I've seen the projects for it, but they are usually only for a single outlet, or to monitor the consumption of one appliance. I want to go to the root of it all and set something up in my breaker panel to monitor each breaker and the power each circuit in my house is consuming, that way I can break it down and see what each electronic/appliance is using per month, but also to see how much we use as a whole all together.

cirano (author)2009-05-19

Anyone know where I can lay my hands on a 220V kill-a-watt unit?

eddcole (author)2008-09-08

Hi can someone put a parts list and wiring diagram of this please and does anyone know how this can be done electronically

mdgnys (author)eddcole2008-12-31

Yeah a simple amp meater should do it but you would have to make the circut yourself.

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