How to shield a live wire at 240V ?

[_q12x_]

I have a electronic board with leds (made by me) that is driving a relay. When that relay is closing it’s contacts, is actually switching the 240V for the light bulb switch in my room. This board is quite long, like 50cm (half a meter). The relay is in the left corner, and the live wires from it goes in behind the board to the hole in the wall for the mains switch. I also have a mild steel sheet behind my board that is grounded. It is shielding the interference of the 50Hz from the live wires from the wall to my sensitive circuit. But even If I have this grounded metal shield behind my board, the live wires from the relay are still affecting my entire circuit board, keeping it ON all the time. If I am disconecting the live wires from the relay, the board is functioning very well. Another IF, is if I disconnect the ground from the metal shield, the circuit board goes nuts. So the shield is doing it's job fine, but only for the live wires inside the wall !!! But not for the wires from the relay to the live switch.
- I want a way to shield these wires !
Thank you !

 

[pc1966]

It seems you are relying on that unscreend supply noise to trigger it when you move close to the antenna!

Also that input MOSFET has little protection so a bit too much charge and you can blow the gate insulator. Having a 10V zener to 0V might be enough to protect it.

Why not have adjustable sensitivity. You could replace the lower 10K off the MOSFET (and some arrangement for driving the LM3914) with a potentiometer so you can set what it needs to trigger?

 

[_q12x_]

It seems you are relying on that unscreend supply noise to trigger it when you move close to the antenna!

Also that input MOSFET has little protection so a bit too much charge and you can blow the gate insulator. Having a 10V zener to 0V might be enough to protect it.

Why not have adjustable sensitivity. You could replace the lower 10K off the MOSFET (and some arrangement for driving the LM3914) with a potentiometer so you can set what it needs to trigger?

Where to put the zenner more precisely? (A zener must have a resistor in series for its protection as well). Can you be kind and make a screenshot on the area of the circuit and draw over it for me, please? Thank you. I really like the protection idea.
I can change little things, but not much. I will try the best I can to change anything I can.
But you see how quickly you defocused from the main issue ? I get that you are refering to the circuit sensitivity... but right now it is a very strong interference I have to keep it out. Not sensitivity. It is working excelent on my table, now I manage it to make it work on my wall as well, but now this problem with wires.
I plan to shield the wires.
Can you give me some advice on properly shield them? Thank you ! I also have an idea, using grounded aluminium foil and a grounded wire inside. Also twisting the the wires I see it is more efficient for shielding. But this is all I got so far.

 

[Lucien Nunes]

it is a very strong interference I have to keep it out.

No, it's just normal house wiring. My electronics lab has unshielded power cables all around it, there is a 3-phase electrical panel with unshielded cables at the end of my workbench and transformers underneath it, there are variable-speed inverter drives in the next room, but everything here works perfectly including studio-grade analogue audio equipment with its covers off.

Personally I would redesign the detector to work a different way, there are lots of options. But at least do something about that floating gate. The diode rectifies stray capacitively coupled noise and charges the gate. But then what? How does the gate discharge? Just leakage? That will vary with temperature and humidity. The Fostex G24S was a 24-track 1" tape deck that had some JFET gates connected directly to diodes, in the monitoring signal switching. These were still showing up as a fault some 30 years after the unit was launched.

Also twisting the the wires I see it is more efficient for shielding.

It's helpful against against electromagnetic coupling, won't make much difference to electrostatic coupling on a screened cable.

 

[_q12x_]

A video update. Nothing is said there that we didnt discussed already. It's a test that failed.
Watch it if you wish.

 

[Megawatt]

I have a electronic board with leds (made by me) that is driving a relay. When that relay is closing it’s contacts, is actually switching the 240V for the light bulb switch in my room. This board is quite long, like 50cm (half a meter). The relay is in the left corner, and the live wires from it goes in behind the board to the hole in the wall for the mains switch. I also have a mild steel sheet behind my board that is grounded. It is shielding the interference of the 50Hz from the live wires from the wall to my sensitive circuit. But even If I have this grounded metal shield behind my board, the live wires from the relay are still affecting my entire circuit board, keeping it ON all the time. If I am disconecting the live wires from the relay, the board is functioning very well. Another IF, is if I disconnect the ground from the metal shield, the circuit board goes nuts. So the shield is doing it's job fine, but only for the live wires inside the wall !!! But not for the wires from the relay to the live switch.
- I want a way to shield these wires !
Thank you !

Have you tried plenum rated cables

 

[_q12x_]

Have you tried plenum rated cables

No and this is the first time I am hearing about them. I just look over some explanations about this plenum cable and from what i understand, the only difference between plenum and non-plenum is the fire hazard non-plenum are. So plenum is the same cable but with a self-extinguishing plastic/isolation cover. Its more about safety with them. But nothing about shielding. So it is not really helping me in my case here. Thank you for mentioning them, I learned something new.

 

[_q12x_]

Personally I would redesign the detector to work a different way, there are lots of options.

Give me all the options you can think of. As many as possible; all of them.
(i also have a backup plan for the sensing circuit as well, but I leave it as the very last alternative, in case everything else fails).
Thank you !

 

[Lucien Nunes]

I don't have time to list all the options. I don't mind giving a few suggestions.

Idea #1. Reflective optical proximity detector with built-in synchronous demodulation e.g. Sharp IS471. Package contains an IR photodiode that is aimed at the detection area. A separate IR LED is also aimed at the detection area and connected to the LED output pin on the IS471. When an IR-reflective object enters the area it reflects pulses from the LED back to the photodiode, which enables the output. The key is in the synchronous demodulation, which rejects even strong IR interference e.g. from room lighting and hot objects, only responding when its own LED pulses are reflected. Obviously you can set the sensitivity by the LED current, beam angle etc.

Advantages - immune to electrical interference. Small and cheap. Easy to fine-tune response.
Disadvantages - Sensitivity depends on IR reflectivity of target. Might not work in direct sunlight.

 

[_q12x_]

Please help !
Another update, this time i made a very short video (2min) where I present the problem.
I inserted the 3'd relay inside the switch socket and I command it with 5V from the 2'd relay.
But the 2'd relay is vibrating like crazy when I power the board.

After that,
I tested it on my working bench and is doing the same. So, no mains interference at all. It is not influenced by the live wires this time.
If I disconnect the 3'd relay from circuit, everything works fine.
If I put 5V on the 3'd relay, is working fine.
My PSU is showing me 1A , sign that something is in short. But Nothing is in short. It behaves as is in short. Only when I connect that 3'd relay. It is weird as hell. I checked for short with my multimeter and nothing is in short. But once I power it up, it goes to 1A straight.
Actually I tested again and is not rising to 1A but to 1.44A ! Way over my custom limit that I set on my PSU . Very-very strange.

 

[_q12x_]

It was a logical error. Im too tired of it probably.
I solved the problem. It was a short after all, but a logical one. Eh... stuff happens.

 

[marconi]

-q12x- : good afternoon. What a nice little project. If you’d like I will try to help you produce a working design. What knowledge do you have of semiconductor electronic circuitry using bjts and fets? Or are you copying designs ( no shame in that) available on the internet?

To help me and you answer this question tell me what kind of transistor is the 2N7002? google and study its data sheet.

is it an enhancement or a depletion mosfet? What do these mean?

is it a p channel or an n channel?

which way around are it’s drain and source connected to the positive and negative rails of the dc supply?

is the way you have drawn the transistor connected for the sensing circuit correct?

Is this the way you have actually connected this mosfet?

There are some clues in my questions.

 

[_q12x_]

- Thank you that you liked my project.

 

[_q12x_]

New update:
The movie is very short (3m40s)
Please watch it, I explain in it what I did and how it works.

 

[marconi]

I have studied your circuitry and am clear on how it is meant to work in theory. There are some aspects of the design which we need to correct to account for contact bounce - the contacts connected to the 555 chip for example and there is no common ground/) 0Volt point for the LM3914. There are far too many long exposed interconnecting leads carrying low currents which are vulnerable to noise pick-up. The way the MOSFET is being used - common drain/source follower - is not suitable nor the lack of any fixed albeit variable bias on the gate of the MOSFET.

A clearly apparent problem is that this MOSFET is permanently 'on'. Not surprising since it is an enhancement mode FET and you have a resistor diode combination connecting its gate to the +5V rail. it takes very little current to charge up the MOSFET's internal gate source capacitance to such a voltage that the so-called gate thresheold voltage Vgs is exceeded which will change the state of the n channel between the drain and source from insulating to conducting. There is no resistor to the ground/0V rail to discharge this voltage. And there is no way to adjust the sensitivity/threshold to change when the MOSFET turns on and off.

The LM3914 is expecting a voltage at its pin 5 which as it rises from 0V to 5V switches its eight outputs on in sequence as the voltage crosses eight voltage values/references. Once can also adjust these voltage values/references by suitable circuitry at pin 8. To achieve the effect of the gradual LED illumination of the wings your sensing circuit is required to produce an output voltage which increases with the proximity of the hand to the antenna. Your sensing circuit is acting as the 0-5V signal source in Figure 1 of the attached datasheet.. but as currently wired your sensing circuit is more likely to just ramp up pin 5 between 0 and 5V and then stick at 5V - so all the LEDS stay on. (Did you check the 2N7002 was actually wired in correctly?)

https://www.ti.com/lit/ds/symlink/lm3914.pdf

Anyway....let us proceed in steps. I do like the way you have constructed the circuit out of sub-systems - very intelligent and shows an engineer's approach to design - well done.

But first things first. We need to have a suitable and reliable power supply. I want you to estimate how much current this supply must deliver at 5V dc when all LEDs are off and then when all LEDs are on. Please show me your working. Also tell me about the power supply - what are you using?


THERE IS AN IMPORTANT CONDITION TO ME WORKING WITH YOU WHICH YOU MUST AGREE TO - YOU ONLY EVER WORK ON THE CIRCUITRY WHEN IT IS DISCONNECTED FROM THE 230v AC BY WHICH I MEAN THE WIRES BETWEEN YOUR CIRCUIT AND THE ORIGINAL SWITCH ARE COMPLETELY REMOVED - AGREED?

And which country or town are you in?

PS: For my own amusement I have ordered some components to attempt what you are doing in a different way in case we are unable to make your circuitry perform as desired.

So - 5Volts dc nice and safe. 230V ac DEADLY!!!!!!

Oh, if you don't already have one please buy a cheap digital voltmeter something like this one I use:

https://www.amazon.co.uk/Compact-Digital-Multitester-Diode-Test/dp/B000L0RINQ

 

[_q12x_]

Mister @marconi , thank you for your kind answer and involvement.
I like your perseverance and I think you like this project as much as I do. Or at least is intriguing to you.
A little introduction first. I am an artist. I am from romania the awesome country where nothing is possible. But I believe things can be done, even if they look impossible. All we need is a bit of ambition. I am not an electronist or electrical guy. I made what I made because I want to make it and because I can. If I could not believe i can, I would not start it. You must understand something. Even if I am not a professional electronist, that doesnt mean I am automatically a rookie. I do electronics for about 30 years, but sporadically (not continuously). So I know something, and for sure I have some gaps, Im not afraid to say it.
You seem to know very good what you are saying. Is my impression. You seem to know more in depth the electronics in general. Probably because (i want to believe) you are doing it all the time. I like it very much and I would love to learn something from you.
There are so many things to cover... I am afraid you will get tired of it very quickly.
First of all, I work alone and simply by that, it is taking a lot of time to accomplish something. I work on this project for 7 months now, and also with any help I could find on internet. People in my country they only say they know, and I believe them, but nobody moved a finger. And is fine by me. People from america, on the other hand, they did got involved very nicely and I have a great deal of respect for them. Im talking about forums, like this one.
I will answer to your questions, indirectly, by giving you some links to my project.
I made a playlist in my youtube channel, where I put all my progress with this project.
How I started, the breadboard tests, failures, problems, finally some achievements, etc. Scroll fast through the movies to not get bored about their long --- content. I am not a good youtuber and I talk unnecessarily too much sometimes. It's also hard for me to translate it live, so that makes me look like an idiot. See the playlist here:
https://www.youtube.com/playlist?list=PL6NJF1kQFOAImsLpNil3wNCb8POZQLYM0
Also, a text to read about this project. I have a description on the page how to download it. It is in a zip form.
q20210117 Led Wings Projekt by q12a on DeviantArt - https://www.deviantart.com/q12a/art/q20210117-Led-Wings-Projekt-867429226
You are welcomed and I also encourage you to browse in my account there, to see my glorious art. If you please.
Here is the online version of the same text to read. You dont have to download anything, but you have to scroll down ... a lot. There are currently 25 artpages.
https://www.artstation.com/artwork/zOBaED
You are welcomed and I also encourage you to browse in my account there, to see my glorious art. If you please. On deviantart I have everything, while on artstation I put only the good and important art.
If you are bored and start to hate my guts, don't tell me. I know. Hahaha.
I am also sorry to not respond to everything you asked me to. Usually I respond, but only to people that are close to me. I am very curious about your response now, after dealing with my mountain of information. Or maybe I am perceiving it as a mountain, because it took so long to make it all... who knows, it's all relative.
Another very important aspect. This project is nearly done. Very close to finish. I only have to discover the source of the interference in my circuit. I mean, I believe everything you said so far and I agree with your diagnostic. But you must understand, that this thing is tested and over-tested, and you come now, ta-da, ta-da, "change the circuit !". It's not easy for me to cut everything I done so far. I can not make any in depth operations for every suggestion I get. So I am patient and cut what I think is absolutly necesary to get as closer as I can to the result I want. If you argument it clear enough to make me believe it is absolutly necesary and it will indeed make it work, then I will listen to your advice. But until then, you are the new guy for me. I will try to make some of your rectifications, but only those that are not very damaging. And also because I work slowly, and Im afraid not to damage it as fragile as it is, it will take time anyway to make all the modifications you are suggesting. In the lack of better ideas, I will try everything I have on my plate, including your advices as well, but it will take time, so please understand. Insist on something that you are 100% it will work and I will give it priority if I believe you enough.
On a final note, All I needed from you here, is a way to stop that interference, to shield it, or to completely avoid it. Its my number one problem to resolve now.
Thank you very much for the support so far ! I will try what I can.