Power Arduino with single 220v live wire

Hello,

I am working on a new circuit and have an idea that I want to implement.

NOTE I am a programmer and working with electronics engineer to do all the hardware for me so don't worry about electrifing myself :grinning:

I am working on a home automation project, I want to build a wireless light switch board that would replace my normal wall light switch.

I know it is easy to power the arduino from 220v mains by using AC to DC converters but this would need me supplying the Live and Neutral wires to the converter.

Since I want my switch to be straight forward and replace my old switch, I will need to power the switch with only 1 live wire without Neutral. ( the normal connection here is having the Live wire only in the switch box and the neutral wire connected directly to the lamp in the celing )

So here is my idea, I want to see if it feasable or not and whats the best practises.

  • I will have a capacitor connected to my board that will be charged.
  • The capacitor will act as a battery to run the circuit.
  • Once the relay or triac turn on lights, I will charge the capacitor again to be used later when light is off.

Question is,

  • Is it feasable to use the live wire only to charge the capacitor?
  • What is the best practise? I have seen several wireless light switches that can be powered with single live wire so I am sure this can be done. ( Livolo switch for an example )

Thanks,
Sameh

You want electricity to run with no return for the electrons? It isn't going to happen. If there is no return path there is no flow.

Hi ChilliTronix,

Thanks for your reply.

I guess my only return will be from the lamp itself, I will have the live connected to the switch and the other line connected directly to the lamp which is connected from the other line to the ground.

Please see the diagram that is showing a working wireless switch with single wire connection.

While the light is off, the lamp itself could serve as a route to neutral. Therefore, it's theoretically possible to wire up a transformer in parallel with the light switch. You would then effectively have a transformer in series with the lamp. This would, however, mean that the lamp fitting would no longer be isolated from live EVEN when turned off. It could also exhibit a glow if your transformer draws too much current. Ironically, in this arrangement, your transformer would be shorted out of the circuit, once the lamp is turned on.

This is all hypothetical though. totally unpractical and downright dangerous. It would be far simpler to route an extra cable to the switch pattress. But if you're going to do that, you might just as well route a suitable power supply for the arduino instead.

Hi KenF,

Thank you for your reply.

So from my understanding, I can charge the capacitor using the live wire and neutral route coming from the lamp while the lamp is off & once the lamp is on I can use the capacitor charge to turn it off again and recharge the capacitors ?

By using capacitors will it limit the danger? is there a better way for this to be done?

[rant]
I know we're not the "mains connection police" and any adult who fiddles with this stuff does so at his or her own risk, but imo it's folly to even think of answering questions like this.

And samehhaddy, if you have access to an ee why are you even asking here anyway? He or she should be engineering you a solution; you ought not to be asking here. No matter how well intentioned the answers are, they cannot be seen as expert opinion on matters where the regulatory and legal implications do not bear thinking about.
[\rant]

samehhady:
Hi KenF,

Thank you for your reply.

So from my understanding, I can charge the capacitor using the live wire and neutral route coming from the lamp while the lamp is off & once the lamp is on I can use the capacitor charge to turn it off again and recharge the capacitors ?

By using capacitors will it limit the danger? is there a better way for this to be done?

The control circuitry itself would have to be fare more sophisticated than you describe it and would possibly warrant a whole project in it's own right.

I don't think your concept of a simple capacitor would be practical. As it would become discharged, in the event that the lamp is turned on too long. Therefore making it impossible to turn the lamp off again. Putting a low value (but high wattage) resistance in the line when the lamp is powered would allow you to draw current in a parasitic mode, even when the lamp is turned on. But as I say, these types of circuits have to be pretty sophisticated to be both safe and reliable. They are also out of my comfort zone.

Thank you KenF, I think Its much safer to go with the 2 wires approach.

Thank you again for your help.

Kind regards.

JimboZA:
[rant]
I know we're not the "mains connection police" and any adult who fiddles with this stuff does so at his or her own risk, but imo it's folly to even think of answering questions like this.[\rant]

I will answer for you....... DON'T EVEN THINK ABOUT IT!

Reminds me of this:

2014-11-17_21-43-56.jpg

LarryD:
Reminds me of this:

Not the best of ideas.

Hi, I think you will find with the wifi switch pictured, when the light is turned ON, there will be a voltage drop across the L to L1 or L2 or L3 terminal, one or all of them will not be zero ohms.
The drop only needs to be 5V to power the wifi electronics, the light brightness would not be noticeably affected.

Many years ago I came across a lamp that had a touch dimmer in it, the dimmer was connected in series with the load, no neutral connection, and when the lamp was at full brightness there was about 7V drop across the two wires to provide power for the circuit.

Tom....... :relaxed:

samehhady:
NOTE I am a programmer and working with electronics engineer to do all the hardware for me so don't worry about electrifing myself
...SNIP.....

  • Is it feasable to use the live wire only to charge the capacitor?

This leads me to wonder about the competence of the electronics engineer - and even his existence.

...R

samehhady:
Please see the diagram that is showing a working wireless switch with single wire connection.

Yes, of course there are electronic switches that work in this "two wire" manner. In fact, your common dimmer does. If you want some "intelligence", then the device needs to have two modes for obtaining power, one for deriving a very small current - insufficient to light the lamp - at the mains voltage when the switch is "open" and efficiently transforming this to a significantly larger current at 5V or so for the "intelligence", and a second mode for deriving power from a rather small voltage drop but with significant current when the switch is "closed". In essence you require two (switchmode) power converters, a step-down from mains to 5V and a step-up from 1V to 5V.

In practice, these electronic switches generally are simply designed instead to use extremely small currents, especially in the "off" mode. Even so, they tend to be incompatible with modern LED luminares which use and respond to very small currents anyway, so that they will tend both to "cipher" and glow dimly when turned "off" and may even provide insufficient current when turned "on", to properly power the electronic switch and so cause erratic operation.

In any case, all such "electronic switches" must be considered to make the circuit "live" even when apparently switched off.

In general, an Arduino requires quite a bit more current to operate (fully) than such ASIC devices, and will be rather impractical.

Hi, the biggest problem I have with the above illustrated device if it has wifi, it has no standards stamps or authority approval registration numbers, and its going to be put inside a WALL.

Tom… :slight_smile:
Almost went into fetal position.

TomGeorge:
Hi, the biggest problem I have with the above illustrated device if it has wifi, it has no standards stamps or authority approval registration numbers, and its going to be put inside a WALL.

You’re so cynical. Look it’s got a gold QC sticker. It must be good. :wink:

QC.jpg

TomGeorge:
it has no standards stamps or authority approval registration numbers,

.... just because you can't read Chinese characters ? ?

...R

Hi,
but its not written in Austrayun, it has to have a "she'll be right" sticker.

Tom...... :slight_smile:
That's bad, I gotta have another coffeeeeeee......... :fearful:

Here are some idea

http://www.atmel.com/Images/Atmel-2566-Single-Phase-Power-Energy-Meter-with-Tamper-Detection_Ap-Notes_AVR465.pdf

Check this