Am I missing something?
Adding a piezo-electric micro-generator to a light switch? Why not just divert a few micro Amps from the current being switched?
Is this just a really bad example?
The ZigBee Alliance - which looks after the low-power radio comms standard - has now introduced wireless communications that are powered by the act of pressing a key. Green Power is an extension to the Zigbee protocol that allows switches and sensors to operate from tiny amounts of power - such as the power generated by the …
The switch in question is not switching a load current, it is a wireless/remote switch. The mechanical action of the switch can be leveraged (no pun intended) to provide the energy to power up a transmitter which then reads and transmits the status of the switch to a controller which then switches the load current accordingly.
Took me a while to figure the gobbledegook out.
That makes far more sense. I have a load of radio operated switch plugs at home with lights stuck in 'em and the remote has a set of rubber buttons to press for on/off.
You should be able to get quite a bit of juice from having a piezoelectric wotsit behind each button without needing any more squeezing than it already does. Probably a zero-sum game for complexity too. As it is, the thing has a PCB with seperate contact patches for each switch so the thing "knows" which switch has been pressed and can issue the right command. Having the thing issue the appropriate command depending on which pin got powered is probably as simple.
The idea of self-powered wireless switches means less mains wiring needed, and you can place the switch wherever you want in the room without having to wire it up to anything.
This is especially helpful for listed buildings where you often need planning permission for alterations.
Its not a great example... imagine a light switch as a signalling device that doesn't need a connection to the mains at all.
The switch simply sits in the wall with a Zigbee radio/piezo power source. You can move the switch freely without rewiring the house. Or add extra swtiches without wiring. Or monitor the light status remotely from a PC. Or link the lights with others and switch them all on at once.
All without signalling wires.
During recent ' Smart watch' threads I was musing on how much energy would be required to transmit a simple control to from a wristwatch to a nearby phone, and whether this energy could be harvested from the button-press.
How small can you go? The only thing I have first hand experience of is the piezo component in 'electronic' cigarette lighters.
It might just be the illustration (in the same way that speed camera signs show a antique bellows camera), but their diagram shows a lever switch- which has a longer throw than many light switches. Since energy is work times distance, is such a big switch required? I guess what I'm asking is "How small a switch is required to transmit these 21 bits 2 metres?"
"Green Power is an extension to the Zigbee protocol that allows switches and sensors to operate from tiny amounts of power - such as the power generated by the physical act of flicking the switch, or from tiny solar cells out of direct sunshine. It offers the promise of a wireless future which doesn't shudder to a halt when the battery runs out."
= "Green power allows switches to operate from the power generated by the physical act of flicking the switch".
This should probably read "Green power allows the status of a switch to be transmitted wirelessly using power generated by the physical act of actuating the (physical, mechanical) switch".
I mean 1 keypress -> 168 bits of data NO local battery (if the device is not a receiver, which if its just for data input it does not need to be).
The "impossible" keyboard.
Is that not mildly impressive?
Obviously self powered sensors for industrial control and alarm systems would be early candidates for this if its secure enough and cannot be spoofed.
> The "impossible" keyboard.
> Completely transparent.
It's not transparent. There is circuitry involved...
> No PCB
You need a PCB.
> No aerial
You need an aerial.
> if its secure enough and cannot be spoofed
ZigBee has encryption built into the standard (AES-256, from memory, but it's been a few years since I've done any). You don't have to turn it on if you don't want to.
Wireless switches sound a great idea - would reduce the cost of wiring a building by a fair amount.
I've got the Phillips Hue system at home which uses Zigbee to communicate with each bulb (you can control each individual bulb locally or remotely via phone, computer, etc). One thing I find annoying is that the hub can't always contact the the furtherest away bulbs (about 10 metres but around corner with thick brick walls). This is probably specific to the Hue system, but I wonder how far the radio signal from these switches will be able to travel and how it'll cope with obstacles.
It sounds like you could do with a repeater in the 'elbow' of your L-shaped room... presumably the bulbs themselves do this?
The signal from the proposed unpowered switches only has to get as far as the next powered node in the mesh network. Since most rooms in your house have a wall socket or a light socket, that should suffice- though yeah, older houses with thick walls and unusual shapes will cause issues. That the switch doesn't require power just means your can place it wherever is most convenient to you, without re-plastering your wall, dangling cables or having to replace batteries.
If we make the reasonable assumption that the target device is going to be, relatively, power hungry there is still going to be need to have electrical outlets. Imagine building the proxy part of the mesh into the fascia of said outlets which could then retransmit to the next proxy either wireless in the same manner (the payload hopping along each enabled fascia) or over the mains wiring (like those Ethernet over mains adapters) to the target.
Replace your outlet fascias and have instant building-wide mesh.
But those IDs change, so that thieves don't intercept and then clone them (in theory!).
Car key fobs transmit a 40 bit code, and also have memory to store the rolling code. The car will accept any of the next 256 of the rolling codes, should you press the fob when you are out of range of your car.
Not entirely, because one of the functions of a remote keylock is to help locate your car in a big car park or long street.
Thought having said that, you would only need that capability when the car park has a substantial number of other cars in it, which implies that there is probably another car near you which could mesh with the others and pass the signal to your own car even when you're too far away from it.
The marketing premise of these energy-havesting light switches is that because they need no batteries or wiring, you can just stick them where you want with velcro. Which means that you can have lots of fun by moving them all around someone's house, so that they appear to randomly turn on lights in other rooms.
Excellent for drunken parties. We need more standards like that.
A typical toggle switch has an activation force of around 1N and a travel (with the old fashioned type) of maybe 10mm, so if we're 100% efficient we'd only get 10mJ of energy. If we assume that piezo mechanism recovers half the energy we get a useable 5 mJ per switching action.
On the other hand
A 3000mAh lithium AA cell has a 15 yr shelf life and provides enough power as 1.6 million activations of that toggle switch. OK they're £2 a go but I can't help thinking that this is solving a non-problem?
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