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 !

 

[_q12x_]

What opamp are you using for your comparator? I have myself a bunch of uA741 in my stock. Unfortunatly I dont have the newest models with rail to rail options. I may try to get in sinc with your tests, using my opamp, if you also have uA741. i'm also curious how you will use it with only +5v and 0V. Usually an opamp uses +5V,0V and -5V.

 

[marconi]

https://www.ti.com/lit/ds/symlink/lm339.pdf?ts=1611642239603&ref_url=https%3A%2F%2Fwww.google.com%2F

I will look in my drawers to see if I have some 741s too so we can use the same opamps.

 

[marconi]

Buna seara la un sicriu roman! Just a quick message - because as usual I am cooking and sitting down with my wife for an evening in front of the television - my electronic components have arrived! I will start to construct your sensing circuit tomorrow morning.

I think we should add a peak detector and low pass filter between the sensing circuit and pin 5 of the LM3914. Something like the circuit I have sketched in the attachment. Most of the 'reliable' pick up by the antenna of of signals from the hand will be due to the mains wiring since it is energised all the time, so a low pass filter which reduces other signals which are picked up beyond 50/60Hz (what is Romanian mains frequency?) will make a difference. No sums done yet by me on component values. You could make a start if you wish. Assume the frequencies beyond 1/2piCR.....

https://www.electronics-tutorials.ws/filter/filter_2.html

 

[marconi]

We will reverse the order of the two circuits I mentioned ie low pass filter and then peak detector.....so that we only find the peak of the 50/60Hz signal. You understand why I have reversed the two circuits?

 

[_q12x_]

Buna seara la un sicriu roman!

Did I offend you in any way so far? Then don't do it to me either. If you dont think im at your level and im just a joke, please dont speak to me and I will also stop writing here. Your intentions are many from what I can see. Why do you call me a romanian coffin ? It is not funny and you deserve plenty of my negative response right now. I will abstain though. Your "familiarity" is starting to become insulting. Please think before you write anything to me. Im not here to dick around. If your romanians friends there are not respecting their compatriots, then that should not be a lesson for you to follow. Usually ignorance is a good remedy for that. I'll give you one more chance to be normal. If you will still continue to "be funny", then I will have to say goodby to individuals like you.
Now... to respond to your question, I am not that familiar with low pass filters or peak detectors. I never use them or feel the use of them.

 

[marconi]

I entered 'good evening to a Romanian boffin' in to google translate from English to Romanian:

https://translate.google.com/?sl=auto&tl=ro&text=good evening to a romanian boffin&op=translate&hl=en

and what I copied and pasted in my message #48 is what appeared: 'buna seara la un sicriu roman'.

Try it yourself please.

I leave it to you, to do the research in order to comprehend what I as someone speaking English in a technical forum intended to say but clearly and mistakenly did not say in Romanian: I intended to address you in a most complimentary way in comparing you to a boffin.

 

[_q12x_]

Thank you for your response and reparation. You see how a single word matters? The translator is not perfect. I checked your link and indeed it translates wrong as you write to me. I was on the point to ignore you for that. But now is ok. I can see you tried something but it come out something totally different. Mistakes happen and I can understand that. It is no problem now.
Have a good night and I will take a more close look over the things you told me.
Also, as I already mentioned already, we also have the same mains as you in England. Also the same coloring codes for the wires. We , as you there, use 240VAC, at 50Hz, and brown and blue for live wires and yellow+green for the ground wire. And is the same for all europe, but i didnt check per say. I think is the same in germany, france, italy, etc. Even in Russia is not that different. I know in china they use 220Vac, so 20V under our new rectifications, but we had 220 also until 2010 i guess. I dont remember when the rectifications took place. Its an entire story about this subject alone, but you have a better idea now.
The only major difference between countries are the power plugs !
This page is very good, at the begining of the page you can find very good sumarized information of our system : Romania Power Cords | Romania Power Cords and AC Cables - http://internationalconfig.com/power-cords-for-romania-ac-power-cords.asp

 

[DPG]

That escalated rapidly!

 

[_q12x_]

We will reverse the order of the two circuits I mentioned ie low pass filter and then peak detector.....so that we only find the peak of the 50/60Hz signal. You understand why I have reversed the two circuits?

Not very well... because I didnt work before with such things. But I can imagine what you are referring to. You want to filter the 50Hz , instead of shielding it. That is a briliant idea and I hope it will work, I really do.
- Again, I bring the discution about IR, I leave IR to the remote control. But I just receive,phenomenally fast this time, my DTMF module, another interesting suggestion from another forum. MT8870 DTMF
I intend to use it for remote control. I have several options for remote control. I never worked with IR so I am expecting 50 IR leds and their receivers. I also already got this 433 Mhz RF Transmitter & Receiver.
also for remote control.
This is a paralel subject to the main discution, and I leave it for the last part, but im telling you about it now, because it is influencing our new option for the sensing circuit.

 

[_q12x_]

Mister @marconi, how is the whether in London now?

 

[marconi]

From left to right:

5V/2A dc regulated PSU...0-5V in 0.55V intervals LED analogue to digital voltmeter (ADVM) - test vernier potentiometer providing 0-5V voltage to DVM.

Tomorrow morning - 3 threshold peak voltage detector - for want of a better descriptor - to filter out spurious maximum voltage signal from ADVM caused by noise and interference.

 

[_q12x_]

From left to right:

5V/2A dc regulated PSU...0-5V in 0.55V intervals LED analogue to digital voltmeter (ADVM) - test vernier potentiometer providing 0-5V voltage to DVM.

Tomorrow morning - 3 threshold peak voltage detector - for want of a better descriptor - to filter out spurious maximum voltage signal from ADVM caused by noise and interference.

It's good that you are back, mister @marconi ! Now I am a bit happy.
It's a bit cryptic for me what you write there. I understand that you use a power source (PSU) for the circuit at 5V and probably set the maximum current at 2A. Mine I set it to 1A and it was more than enough and more safe. But the rest ?!? Again, i am not that familiar with the peak detectors or low pass filters that you are going to test. I have an idea about their existence but never worked with them.
I really hope your idea will succeed and that you will be able to teach me how to make it work in my side after that.
I thought on your idea and I can not make any logical connections between peak detectors and low pass filter and how to stop the 50Hz interference and allow only my hand interference to be "seen". I really hope you can make it. Probably you have far more better instrumentation than I have, and that will guide you probably straight in the hearth of the problem and resolve it. But is my guess. Im very curious what you can do ! Good luck !
I've also watched your movie, and then mister David movie from EEVBlog about peak detectors, link here:

and he is explaining them very well. But even such briliant explanation I still cant find in my mind the links to actually filter only the 50hz and leave my hand interference open to sensor. I dont have that kind of experience and knowledge and thats why i can't link anything in my head.
But is a fascinating idea that you have here, and for sure, like I said, with very good instrumentation you can find some sort of weak spot that can be used.

 

[marconi]

We decided to have a take away so while we waited I ‘stabbed’ the breadboard a little more to make the three level detector (TLD) for testing tomorrow morning. The three red LEDs at a slant indicate when each of three three levels have been crossed. The final output will be fed to an edge detector which will then toggle a relay on and off to control a lamp. Or something along these lines.

 

[_q12x_]

All I understand is that tomorrow morning you will do some testing. But nobody knows on what. We'll see what you get, after. Good luck there.

 

[marconi]

Output signal from three level detector passes to leading edge detector whose output is the input to a JK flip flop Toggle switch which operates single red Led to the top left.

Next step is to connect Toggle switch to relay to control mains lamp......