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_]

Are those two holes above the switch in a region where the cable might be run in the wall?
No. THose are my holes, made by me when I installed the light beam switch, remember? 1 year ago.
There might be a damaged line conductor in the cable run to the switch box.
These are powerful strongly and consistent comunist blocks, they dont have trivial issues like damaged conductors in them. Haha, but seriously, they were build to last and not to crack, like today products, in comparison. Its the truth I know and experience. You will probably dont agree. But Im telling you how it is from my side of the board here. So, nothing can be broken inside by itself, only broken deliberately.
But... now, after I tested it with my DMM... hmmm I start to think maybe you are right.
and then measure the potential difference to earth of the wall in the region (shown in yellow in my diagram) where the wings would fit.
I Just did it. I put my DMM (digital multi meter) on 20VAC and the red probe on the grounded wire. Actually, while the probes are in air, not touching anything, DMM reads like 0.1-0.3V by itself. Its an old DMM and I dont trust it completely. Is having some leaks, and I know it has. Is not perfect. Now, when I link the grounded wire with red probe, it jumps to 6.4V while the black probe is in air, in my other hand. When I circle with my black probe directly on the wall, and around the 220 switch hole, it jumps to 7.8 and the closer I get to the hole it reaches 8V.
I noticed that the hole is not cement but an iron tube inserted in the wall, with some holes in it for the wires to pass through it. When I touch this rusty metal case, I get an instant 19.7VAC.
Thank you for putting me to take this measure! Alone I would had not do it. That explains it then.
I might power my entire circuit to this electric field alone, with no transformer at all. hahahaha.
Who knows, maybe its like that by design... some countermeasure of some kind. Very weird. I know this block is a special one, because is central in the city. They made the best in the center, and the prefabricated ones on the sides, all around the city. THese were supposed to be for high demnitaries and party high valued members. But then capitalism happened and all got to ---- like we all know it is today. We got lucky to get this appartment since we had a house and the state back then evacuated us from it, took "it's" land back, and pretty big land it was, and give us in return this "esteemed" apartment. And its extremly well made. No doubts about it. Too much unnecesary history. Haha. My point is, maybe its by design, but we never knew it. Very interesting for me as well, and i imagine for a stranger from another place and county like yourself is fascinating probably.

 

[_q12x_]

Have courage - you know now it can work as you desired....so for that reason I have not changed my 'Winner's star' award to you!
It's very nice to see someone is trusting my judgement. Usually people are ignorant about miself, and is fine, is a good camouflage. I got used to being ignored. And sometimes Huuu-ed. Life and citizens, I never like them either. Hahaha.
I built another SCM. And now is working fine again.
It might be that the older one was "worked" too much and it started to leak is my beast guess. Especially the cardboard being most probably soaked from my fingers. It is a possibility I think why it got wild by burning 2 transistors and then complete death. RIP old SCM. We will forever remember you.
I made a movie, a bit too long [11min] and really not that important, you can skip it if you like. Basically I talked about these transistors how they got burned, and the new module that I made, Im making this movie, as a proof that is working now when the 0V wire is not connected to the shield. I'ts a possible cause that those sensible transistors got burned. Not completely sure, but is an idea.

 

[_q12x_]

Newsflash !
I burned another 2 transistors only by switching the antena ! WOW.
SO I have 4 burned 2N7004 now. It is a confirmation that is from the antena.
I think the length of the antena is just overwhelming it's gate.
I think that pot in the circuit might help with this problem. Im thinking to add 2 x 5k on the pads where the diode is; where the pot should be.
Unbelievable. Why now? Why not before when I was switching the antena length like 100 times. It is weirder and weirder. And I did not connected the 0V to the shield this time. So that has no influence.
Maybe some other components failed and is dragging down this module, hyper sensitizing it.
Is the most strangest project and circuit I ever encountered and built.
Im starting to think is a good idea to make a theremin circuit - seriously. Im too tired from this braking all the time. Its too fragile.

 

[_q12x_]

It just occur to me:
Do you know how can I intimately read this 2N7000? Because as you know already, the osciloscope or DMM are not usable, they interfere and keep the transistor High. A PIC microcontroller ! That will intimately read all this weird behavior. But I dont have prepared for this step, it's too deep for me, I know how but everything is not in order at this time to do it like that. But is probably the best thing. Also range calibration from the pic as well. It's an idea.

 

[marconi]

Good morning. I have just got up and am sat slowly reading through your latest posts with a good cup of strong coffee. I have not had time yet to think about what you have written; I will do that this morning and reply later.

I have spent now a couple of days trying to replicate your situation in my shed but to no avail - I simply cannot produce the electrical interference and obviously I do not have your wings board in front of me which is 'part and parcel' of the way the electrical interference is being picked up and then disrupting the operation of the circuits. I mentioned earlier 'my criticisms' of the proximity sensing circuit you are using one of which to work it relies on a very high input resistance at the gate of the MOSFET; this very high input resistance makes it extremely sensitive to any and every small current incuding of course from the antenna. The gate source junction of a MOSFET is very much like a small capacitor (a reverse biased diode with two conducting ends) which means it does not take much to charge it. It is also a physically very thin junction and prone to damage including from over-voltage. Such over-voltage may be from the mains pick-up or static-electricity. It could be this kind of damage which is damaging your 2N7000 transistors. The strongest I will put it to you now is that maybe the time has come to reconsider the use of this SCM and instead to use some other design which is active-passive as I did with the IR diodes. Here is a little more on ESD:

ESD Effects: How ESD Affects Electronics » Electronics Notes - https://www.electronics-notes.com/articles/constructional_techniques/electrostatic-discharge/esd-effects-how-affects-electronics.php

I will now read your posts carefully, have a think, read some books and then draw some diagrams before replying later today.

Keep smiling!

 

[marconi]

I thought I would quickly mention three observations after I re-read and re-watched all you have said and filmed.

It seems to me there are the following differences between the wings board on the bench and then on the wall. On the bench all (nearly all functions correctly) whereas on the wall there are problems:

1. On the bench you use a lab power supply whereas on the wall you use something else - the modified 220V - 5V adapter;

2. On the bench the metal board is 'connected' to earth by contact whereas on the wall the board is not unless you provide an earth to it. Is the metal board screwed to the wall?

3. On the bench the twisted pair from the RDM2 to the 220V lamp relay is run away to the left to your test lamp whereas on the wall this twisted pair is 'sandwiched' between the wall and the metal board for about 600mm.

4. From your voltmeter tests of the wall potential with reference to earth it seems the wall is at some arbitrary potential above earth potential.

5. The twisted pair passes through a small hole in the metal board.

6. The point to which you connect to obtain ground/earth potential might actually not be at true ground potential ie 0Volts - perhaps because of your home's type of earthing system and earth leakage currents from earthed equipment in your home flowing to earth and raising the potential of it with respect to true earth/ground. Is your home on the ground floor?

It would interesting to see what happens when you run the twisted pair from RDM2 to your test lamp sandwiched between your bench and the wings board. And also what happens when this twisted pair is re-routed to connect to the the RDM2 from above the board rather than through this hole.

Could you take a picture and post it of your home's electrical cupboard including the thick earthing cabling? Attached is a UK example:

 

[_q12x_]

Thank you for taking time to read all my experiments.
All your points are valid points as well.
All 4 are burned on my testing bench and not on my wall this time. I forget to mention this detail. But usually, I am quite explicit, when im filming on the wall, is a wall problem and when im filming on the bench, is a bench problem. And Im also specifying, usually. So this is it. I think something just give up in my entire circuit. Who knows what. Damn, so close.
The electrical panel in my home... pfff, in the first place, is not my home is my father home and he just left that forgotten from when the block was built, so it's kind of disaster there, all the wires, from how they were from construction times. Nobody touch them. Its like a ball of wires untouched by living beings. And all have the same color, white. Naaah, its a disgrace. I dont like it, but also I cant get into it also. THat is out of my jurisdiction, morality and legality even. So... it might be some weird sh*t coming from there,as you say.
But the wall is not the issue anymore, we kind of resolve it.
Now on the bench, I got weird results. I keep thinking that grounding the 0V rail from my circuit, might unbalanced or disturbed the other components, the entire circuit even. And now, when I connect the SCM, it is too fragile because of the entire changes... I know, I know, its speculation to the sky and back. But before the breakthrough with grounding the 0V, I could change the antena and nothing got burned.
Its just... too delicate, too breakable. It's not a solid circuit what I built so far. Pity. And 7 months to drain.
Yes, I can work with it like this, but.... its not that cool, and risky that it will break again, just because.
What a project.... Ha. Only a romanian could start it. Haha.

 

[_q12x_]

A challenge:
Draw over my sketch, or make another new sketch, completely from 0, and show me how you would do it.
You have my experience with what is good and bad. Make me your version. Completely different from mine, or similar, I dont care, just make it more stronger and solid and serious than what I did so far.
But make it clear and understandable not enigmatic and romantic that nobody will understand it's functionality.
In other words, if you plan to make it, how would you make it?

 

[marconi]

I think you ought to take break from this project if only to rest your mind. Even away from the bench though your mind will be pondering on the project so it is not doing nothing. I will contact you later.

 

[marconi]

A couple of attachments to show my SCM as constructed.

 

[marconi]

And here are my morning’s thoughts on the electrical situation of your circuit boards ( the red line) and of the antenna. These are working scribbles which I hope will make sense to you.

You will see I hope that the ac potential Vb of the wings circuitry ( all modules) and the antenna with respect to earth/ground is highly indeterminate because of the variation of the couplings to 220V and to earth as I have attempted to illustrate.

Even when you place your hand near the circuitry or the antenna the potential of your hand is highly variable.

This goes someway to explain why the location of the board on the bench or wall makes a difference and also how the wire to the lamp relay from the RDM2 will change coupling and hence the potential Vb of the circuits or antenna. It is unsurprising that the performance of the rudimentary SCM circuit is badly affected since it is so sensitive.

I will address the question of what to do about this next after some more thought.

ps: Millman’s theorem is an easy way to establish the potential of a node which is energised by different sources of voltage via different resistors/impedance when all the voltage sources are all connected on one side to a common point in our case earth/ground.

 

[marconi]

What next?

1. Background and context. This project is demanding because you want to be able to sense your hand - and nothing else - as it approaches a sensor; and when the hand is close enough you to sequentially illuminate as series of lamps in the shape of a wing; you want the intervals between lamp illuminations to be nearly constant and closely linked to distance intervals between your hand and the origin of the sensor. Your dome diagram summarises this well. Furthermore you want the detection zone to be a dome and for the response to tbe the same whatever the direction of the radial you hand moves along. You do not want anything to happen outside the domed region. You want the same hand movement to turn the lamp off as it did to turn on. You do not want random or spurious turn on or turn off. You want only one attempt each time to turn on or off. What I called reliable.

2. Ways of sensing the hand, its distance from the sensor and angle of approach. In one form or another energy has to be received by the sensor from the hand. It is highly beneficial to have a high energy return from the hand compared to any background noise or background clutter. This way the presence of the hand is detectable with a higher priority of success and lower priority of false detection. In signal processing terms you want a high signal to noise when the hand is in the region(dome) to be detected and a low signal to noise outside. Or you have to set up a threshold for S/N greater than which a hand is deemed present and lower than which it is deemed absent. Setting the threshold high will reduce false detections but also reduce the probability that a hand will be deemed present. And too low hands will be deemed to be present when they are not. A balancing act then. Considering the noise and clutter signals picked up by the sensor, some parts of the frequency spectrum are better than others. You have discovered that the frequency spectrum around mains electrical power supplies is both noisy and cluttered. The sheer 'volume' of electrical signals at 50 Hz and close to it means detecting 50Hz signals off a hand will be hard to differentiate from noise and clutter. Any sensor detector then that operates at 50Hz is highly likely to perform poorly. This you have discovered with the SCM circuit.

3. Filtering - spatial and electrical. One could attempt to 'narrow down' the field of view of the sensor to only 'see' a hand presented in its region and hope that at the same time less 50Hz noise and clutter are seen too. Once can attempt to suppress or ignore by electrical filters noise and clutter signals arriving from unwanted sources and along unavoidable routes (ie connection wires). These can help but all have the effect of reducing the ability of the sensor to achieve the desired user performance mentioned in paragraph 1. A conclusion then is that a hand sensor, be it passive-passive or active-passive, operating at 50Hz (or close) is an unsuitable technology.

4. Conclusion. You have undertaken a first-class technological evaluation of the passive-passive SCM circuit and discovered it to be beyond question unsuitable and unreliable to satisfy your project requirement. You did not know that before and nor did you know why not. Now you do. And that passive-passive sensing is highly limited; active-passive is the way ahead.

5. Next steps 1. More briefly now - my evaluation is that the remaining circuitry is fit for purpose and reliable. You showed this - please confirm - by fixing the board on the wall and replacing the SCM with a potentiometer. In this set up, when you rotate the pot' and deliver a voltage over the range 0-5V all the functionality you want and expect from the remaining modules is produced and reliably. You then only need to work on a second generation SCM using different technology to provide a Vs signal over the range 0-5V which even before you start know will not have the same drawbacks as the first generation SCM. A fresh challenge for you.

6. Next steps 2 - safety. As a professional electrical engineer the section of circuitry comprising of the output of the RDM2, twisted pair, 5V SPST relay, and connections of Line and Switvched line at 220Vac to control the lamp is physically unsafe and makes me worry greatly. I can help you select a better physical realisation of this section which properly separates and isolates 220V ac form the 5V dc. A plastic box to put it in is a must for one thing you must do. A cardboard wrap is not enough protection. The first and last requirement is for the design to be safe and remain safe in service.

7. I demonstrated an IR sensor which at least showed it had some potential to meet your requirements in paragraph 1. But you could use other technologies - ultrasonic maybe. You have I think already done some research on alternatives.

Let me know what you think or ask me to lie low for a while while you do more research to satisfy your own mind.

Regards

Marconi

 

[_q12x_]

Yah... Good report. Not what I asked, but I respect it either way.
I understand your point with the active SCM as being version 2.
Again, can you draw me your version of SCM ? How you will do it?

 

[marconi]

Yah... Good report. Not what I asked, but I respect it either way.
I understand your point with the active SCM as being version 2.
Again, can you draw me your version of SCM ? How you will do it?

I have drawn already and posted the circuits for my prototype ir sensor mark 3 with a ‘two IR led illuminator + one photodiode receiver’ and a video clip of it detecting my hand as it approaches, clears and remains fixed.

The video clip mp4 shows the rising and falling and steady illumination of the column of 8 yellow LEDs as these hand movements happen. Each yellow LED of my column of 8 LEDs represents one group of your 8 groups of blue LEDs which illuminate your wings.

My ir sensor mk3 outputs a 0 to 5V Vs signal which could be the input to pin 5 of your lm3914.

I will check I posted the ir sensor mk3 circuit- I thought I had. It looks like I may not.

I did phew ....See #102 attachment for circuit transistor is a bc547b.

 

[_q12x_]

I have drawn already and posted the circuits for my prototype ir sensor mark 3 with a ‘two IR led illuminator + one photodiode receiver’ and a video clip of it detecting my hand as it approaches, clears and remains fixed.

The video clip mp4 shows the rising and falling and steady illumination of the column of 8 yellow LEDs as these hand movements happen. Each yellow LED of my column of 8 LEDs represents one group of your 8 groups of blue LEDs which illuminate your wings.

My ir sensor mk3 outputs a 0 to 5V Vs signal which could be the input to pin 5 of your lm3914.

I will check I posted the ir sensor mk3 circuit- I thought I had. It looks like I may not.

I did phew ....See #102 attachment for circuit transistor is a bc547b.

So this is your definitive solution? The IR ?
I actually did something similar, when I made the beam light switch. It used a normal led and a LDR back then. But this one now, is an upgrade to that. Is not the same configuration as my old one but is the same principle. So in a sense, what im saying is, that I've already did it as you now suggesting.
Of course, your new configuration approaches more to my semi-sphere concept and is superior from my original beam light switch. I will give it a try, but as you experimented already, the range is very small like 1-5cm if I'm correct. I want a range around 20-40 cm to be usable. That's 1 of the important points of this project. My SCM is able to reach to around 15cm with a small antena but I made tests a couple months ago with longer antena and I got like 50cm range with it. Now is a problem of electrostatic buildup, because the weather as discussed already in another forum, so the longer antena is damaging the gate of the transistor with voltage higher than its 20V permitted. What a sh*ty situation. Only happens to me. Maybe is good that it happens now and not later.
More than that, IR or led beams are liniar and not 3d or spherical as I want it. In other words, I have to HIT that line between the led and its LDR. That was the reason I abandoned the first projekt and started this upgraded one. This is actually it's upgrade. And even as you put it, with cones of light, I still have to target it, until I find it and then switching. Ugh... But is having potential and I did not try it yet and also did not give it my best as I do now with my SCM.
Do you see now, why I choose SCM over IR or LED ? It's logical, yes?