Hi everyone,

I thought I'd post here to ask for a bit of help/guidance on our proposed senior electronics design project. We're calling our project the Power saving outlet. The idea is to cut ALL power to a device when you switch it off. Many devices I've noticed (TV, radio, guitar effects pedals) are all drawing current even when switched off. I've come up with a very basic idea on how I think it should work, and am in need of someone to tell me if I'm on the right track.

The outlet will consist of some kind of a current measuring device, in line with the 120V mains supply. I was thinking of maybe using a standard Ammeter, and then pulling the value from it. Not quite sure how that would be done. Anyway you plug your device into this outlet, and turn your device off. Then there will be a "SET" button on the outlet. You press this button and it records the value of current in the wires. This Iset is the current the device draws when it is turned off. Now a microcontroller on board will look for conditions in which Iwires = Iset, and activate a relay (maybe) and cut all power to the device. Does that sound plausible?

If this works, I'm a little unsure of the next step, which is how to actually give power to the device when you want to turn it on. Somehow pressing the power button on the device will have to deactivate the relay?

Anyway I would very much appreciate anyone who has any kind of input at all. We have already proposed this idea to our professor, but he wants us to elaborate on it. I told him everything I've written above, but at this point I haven't done much research related to a much more low-level functioning of this design. A big thanks to anyone who can point me in the right direction.

 

There is a simple solution. Plug your TV/radio/device into a power bar with an ON/OFF switch.

 

I should have mentioned that you will be able to control each outlet on the strip independently. So if there are six receptacles, each will have it's own "SET" button so that you don't have to kill all power to the strip. You may want to keep some things on, other things on standby, and other things off completely. Yes, you could get around this by having all different outlet strips and manually shutting off the ones you want. But the point of this project is to eliminate that hassle.

 

Ok. Unplug your device.

 

That is one option. But a lot of times your devices are not able to be unplugged conveniently. For example if I had to unplug my TV everytime I didn't want to use it I would have to move the entire shelf and scratch the floor, hurt my back, etc. I think you get the point. No, it is not the most brilliant idea ever. I am not claiming that. I am just asking for some design advice.

 

It has already been done. Look up smart power strip.

The issue is one device will always need to be plugged in. The TV for example needs to be plugged in for the power switch to work.

 

That is one option. But a lot of times your devices are not able to be unplugged conveniently. For example if I had to unplug my TV everytime I didn't want to use it I would have to move the entire shelf and scratch the floor, hurt my back, etc. I think you get the point. No, it is not the most brilliant idea ever. I am not claiming that. I am just asking for some design advice.

Ok. Install an inline switch on the power cord.

(I'm not trying to be facetious. Just suggesting that there are some low-tech solutions that are less costly.)

 

It has already been done. Look up smart power strip.

The issue is one device will always need to be plugged in. The TV for example needs to be plugged in for the power switch to work.

Looking at a few of these devices, it seems they have specified receptacles for specified devices. For example, plug your TV in here, your printer in here, etc, etc. I think what would separate my device from theirs is that it is a universal form of this. It will *ideally* work with anything. And even if there is something out there exactly like it, it's not a total deal breaker. I can still design my own version for the school project. Now are you saying the problem with my proposed design is one thing always needs to be plugged in? Could you explain why?

Ok. Install an inline switch on the power cord.

(I'm not trying to be facetious. Just suggesting that there are some low-tech solutions that are less costly.)

The thing is this is a school project. I get that this is not the most economically viable idea. Many other groups have design ideas which you could make the same arguments for. The idea of the project is to learn how to follow the design process, and make mistakes along the way and learn from them. I'm sure you understand this. I am not aiming to come up with a brilliant invention that is cost effective, cheap to produce, easy to use and revolutionizes the world. We have a time frame of several months over which the point is to learn about electronics design and engineering in general.

 

Ok. Then how about a watt-meter that indicates the amount of power being drawn by the device?

 

Well, we had already decided on this. That's why I'm asking several things about this design.

 

Looking at a few of these devices, it seems they have specified receptacles for specified devices. For example, plug your TV in here, your printer in here, etc, etc. I think what would separate my device from theirs is that it is a universal form of this. It will *ideally* work with anything. And even if there is something out there exactly like it, it's not a total deal breaker. I can still design my own version for the school project. Now are you saying the problem with my proposed design is one thing always needs to be plugged in? Could you explain why?

That is not how they work. You have a master plug and slave plugs.

When current drops below a set threshold on the master, it shuts off the slaves. Current rise above the threshold and the devices turn on.

Something like a TV is always on standby. For what reason a modern LCD is that way I am not sure. Probably just so the remote will work.

Oh an the strip is powered too. If you really want to safe on power Mr. Chips has the right idea.

 

For devices like tvs you could have it respond to the same code as tv.
Then ir blast to the actual device to turn it on.

Not practical, but better than 3 legged underwear.

 

While school projects don't have to pass the same smell tests as real products, those factors are still factors that should be addressed in the design and in the report.

One point to consider is the basic premise -- we want to remove power to devices that always draw some current even when they are "off" in order to save energy. So think about the solution you propose -- having a device that is always drawing power in order to sense when to shut power off to something and then have it always drawing power in order to sense when to turn power back on. If you are going to pursue this project, then the final report should include a pretty thorough analysis of how much power you save versus how much power you consume to do so.

 

if you turn off all power to the device, how can you tell if the device is turned back on?

 

There is a reason why most devices have some things always running. Remote controls need something to talk to.

Another problem might be that you have to differentiate between off current and on current or nothing will ever turn on.

 

The critical flaw in the idea is (as people have said); that once an outlet is turned off how does it turn back on?

You need to solve that at the design overview stage, before moving on to the design itself.

There are a number of options how you can do it, so suggest all the ones you can think of, and if you can't decide from your list then maybe we can offer suggestions.

 

There is a flaw in your project, not at the design stage but at the concept level, as RB has pointed out.

1) How do you turn the unit back on? Devices are turned on/off using a push button either on the unit itself or via a remote controller. In your project concept, the user will have to push two buttons instead of one unless you use a remote controller that activates both the power controller and the device.

2) Modern electronics already have build-in low power controllers. You are making the assumption that you can design a power controller that consumes less power than what is already on the device.

 

The TV for example needs to be plugged in for the power switch to work.

If you say so... (giggle) perhaps not quite lucky with that statement, but see what you meant to say

 

There is a simple solution. Plug your TV/radio/device into a power bar with an ON/OFF switch.

People! Do not forget that this is a school/uni project. It shall be a part in a learning process, and not end up product you get in the store. Try to help with that in mind

 

I still think that designing a power meter is a viable project which will need to contain similar components as the original proposal since both projects have to be able to measure the power consumption of the device attached.