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_]

Yes, now is good, I could see the video. It's an .mp4 format, that is what web loves these days.
What are those 2 ? It appear like a photodiode and a IR led ?

I like how is switching.
But please, make me a circuit diagram of what you did here. Exactly. You used some logic there that is very interesting. Draw it on paper, and make it nice and make a good resolution photo of it.
I still wait for my IR leds to come from coronavirus... aaaa, China.
My problem is still my wall interference that im fighting with. In your case and many others, if you dont have strong daylight (like I have) on your wall, you can use your IR leds as you have now. In the end I will try it as well, but first to get them in mail.
You still wait for your 2n7002 transistors? You said you took some. If i remember right.
You said you will duplicate my experiment on the wall near the mains. This is way out of my league.
What i did so far, is not much. I made a simple AC detector, that doesnt work on my wall, but only on my table. I think it's sensing my grounded table. If I lift it in air, its led is lit for a considerable distance from table, from about 20 cm and forward.
Is working somehow, but not really sensing what I need.

Here is in the air(led is on):______________Here is near the table (and led is off):

________________

 

[marconi]

The two silver components you took a picture of are the IR LED and IR photodiode I provided the datasheets for. I am passing about 20mA through the IR LED - the limit is 100mA but I am avoiding operating near the limits to begin with. The forward bias voltage of the IR LED is about 1.5V so a simple estimate of its IR power output is 1.5 x 0.02 = 0.03Watts within its cone of shine (red fan in my attached diagram). The IR LED is my torch to illuminate the hand or whatever else appears in front of the second diode, the IR photodiode. This diode has a 10 to 15 degrees cone 'look' (dark grey fan) which is why the two components - IR LED and IR photodiode are angled towards each other - see my diagram. Today I am going to make another identical IR sensor but using a 40 degrees look photodiode - this will have a larger 'aperture' and thus I hope capture more of the reflected IR beam off the hand but at the risk of other reflected IR energy from nearby objects - so called 'clutter'.

Yes I have some 2N2007 transistors. I plan to work on the type of sensing circuit you have used at first and drawn a circuit diagram. To avoid unwanted pick of mains voltage in anything but the antenna I am going to use some micro-coax to screen the signal between the antenna and the circuitry - but it has yet to arrive - maybe next week sometime.

https://static.rapidonline.com/pdf/51-6094.pdf

This is the 5V SPST 230V ac 5A OMRON relay I selected because it is a good make and the insulation resistance (1000MOhms at 500V ac) and dielectric strength (3000V ac for 1 minute) between the 5V side and the mains side are very high. I will post a picture of how I located it within the oblong white connector block.

https://static.rapidonline.com/pdf/60-2476.pdf

One of the challenges I have set myself it to only use one breadboard. As you can see there is not much room left for the sensing circuit. I have made a wooden post (top right) with an in-line socket glued to it. I can plug in my prototype IR and body voltage sensors to this socket. I will post a close-up of what it looks like later on today. At the moment only 3 of the sockets 10 pins have been used - 0V, 5V and Vs the voltage signal output from the sensor.

 

[marconi]

I was able to use the plastic shields inside the oblong connector to provide some more insulation between the 5V and 230V circuitry.

The IR sensor is reverse biased photodiode connected between the collector and base of a common collector connected npn small signal transistor. The emitter is connected to 0V via a 1kOhm resistor. The Vs sensor signal is developed across this resistor. The IR led is connected across 5V supply via a 220 Ohm resistor.

 

[_q12x_]

Thank you for your explanations ! I understand better now, that the 2 components have diferent cones angles as the red and black as you draw them. Very good. i didnt know that information. It's interesting to have an idea about them. Thank you. I am new to IR in general, so every bit of information is gold to me.
But you still didnt made me your circuit diagram, I still find it intriguing. It works very nice so far, very close to what I did. It will also help you clarify your thoughts, even if you think you know how it works. I know it does to me.
Yes, use coaxial cable. Do anything you can do to diminish the 50Hz interference ! That is this project goal. If we can do it, then it is a successful and finished projekt. If not... then I have to rethink it's usefulness, and keep it away from 50Hs mains. Use every coaxial you can find, every idea you may have, just hammer it until something give signs of properly shielding that thing. And ask your friends as well, my friends suddenly they dont know electronics anymore after my inquiries and they are very busy. Hahaha.
And as always, thank you for your help so far.

 

[marconi]

I will draw my circuits once I am happy with them.

The problem with a circuit like the one in #76 is that it not at all selective in which signal it picks up and amplifies to produce a current to light the led and in my case to produce the sensor output voltage Vs. The antenna and transistor is acting like a radio without any tuning. What I will attempt to do first of all is to restrict the reception of the circuit to 50Hz. So, if one takes the small signal from the antenna and passes it through a low pass filter with a cut off frequency of say 100Hz all those interfering signal beyond 100Hz will be tuned out.

One also has to design the circuit and its construction so that only the antenna is picking up 50Hz signals. As a bare circuit with everything exposed it is unavoidable that all the parts of the circuit will pick up 50Hz. Somehow we have to prevent that.

Anyway, work in progress and interesting too. ?

 

[_q12x_]

Anyway, work in progress and interesting too. ?

I am very angry on this last rock in my way, with the 50hz from the wall. It was hard to make it so far, now is even harder. Imagine how i feel.
From what I understand, my body is like an antena and receives the 50hz from the mains. The 2n7002 transistor is picking up my 50Hz that I receive from the 50hz in the walls. This is the funny part. We must stop receiveing the 50hz from the wall, but allow my 50hz from my body.
My plan is to first pick the signal in the wall, and efectively draw on the wall the position of the wires.
Next is to make a more insensitive SCM (sensing circuit module) than the current one. This one I have with 2n7002 is too sensitive. I plan to make it less sensitive and somehow, balance to not feel the wall fv, but be only sensible to my body. It's an idea and a lot to experiment. But is a way.
I am also thinking on shielding techniques. So far... i have nothing but if I shield the 50hz from the wall, game over, chess mate. I understand your point that it might be the circuit itself a possible solution to the problem, by tweaking it, but I am also after brute force, it never disappoint me.

 

[marconi]

The other practical thing to do is to make the antenna less receptive in some directions and more receptive in other directions. We refer here to the directionality of an antenna. The shape and size of the antenna influences the directionality. You have already been experimenting with an antenna‘s shape and size and there effect on directionality.

Without any discussion right now, we need to design an antenna receptive to the alternating electric field of the mains wiring. If we are clever enough we can make the sensor only receptive and sensitive in a direction along which we want to detect the hand and to be ’electrically deaf’ to the mains electric field being radiated in other directions. A bit like the way the IR photodiode has a cone/fan shaped region of detection.

 

[_q12x_]

Good idea with the cone of detection. But how?
Another idea I have , is to use another type of circuit that is NOT using 2n7002, is what im trying with these new sensing circuits, with 3 transistors and another fail I made today with an opamp uA741 that doesnt work at all. The idea is to have a secondary sensing circuit (B) only for the 50Hz, somewhere in the left of the board. I want it to not be sensitive to my hand, but only to the 50Hz. My (A) 2n7002 circuit is sensing both my hand and 50hz. On its output to pin5, some sort of module that will compute A-B and output basically only my hand fv to the pin5.
I had to make this AC sensing circuit long time ago. So I am making it now, with double purpose. Is a bit parallel with my main objective but... I have to try it.
I start to have the impression that my hand and the 50hz from the wall is the same thing for the transistor. Only that my signal is not that strong as the one from the wall for him. I was having the impression I have another fv or signal, very different from the one in the wall. But now i realize is probably the same thing, but at different intensities/volume. So in a way, is impossible to separate them only from electronics, and we need to have a very good testing apparatus to find a clear path between all these interference to actually make it do what I want it to do.

 

[DPG]

Good idea with the cone of detection. But how?
Another idea I have , is to use another type of circuit that is NOT using 2n7002, is what im trying with these new sensing circuits, with 3 transistors and another fail I made today with an opamp uA741 that doesnt work at all. The idea is to have a secondary sensing circuit (B) only for the 50Hz, somewhere in the left of the board. I want it to not be sensitive to my hand, but only to the 50Hz. My (A) 2n7002 circuit is sensing both my hand and 50hz. On its output to pin5, some sort of module that will compute A-B and output basically only my hand fv to the pin5.
I had to make this AC sensing circuit long time ago. So I am making it now, with double purpose. Is a bit parallel with my main objective but... I have to try it.
I start to have the impression that my hand and the 50hz from the wall is the same thing for the transistor. Only that my signal is not that strong as the one from the wall for him. I was having the impression I have another fv or signal, very different from the one in the wall. But now i realize is probably the same thing, but at different intensities/volume. So in a way, is impossible to separate them only from electronics, and we need to have a very good testing apparatus to find a clear path between all these interference to actually make it do what I want it to do.

I've followed this thread for a few days now, and am very impressed with Marconi's efforts (as always).

But.... can you confirm what the actual requirements are? What are you aiming for?

 

[_q12x_]

What are you aiming for?

The aim here is to get rid of that 50Hz interference. Simple. To shield it or to cheat it.

 

[stevethesparks]

Not really my expertise - just an amateur, but would it not be possible to make a pass through filter or band stop filter designed for 50Hz to sink/block the interference? (one would be wired in parallel the other in series)
Hope I'm not interfering.

 

[_q12x_]

Not really my expertise - just an amateur, but would it not be possible to make a pass through filter or band stop filter designed for 50Hz to sink/block the interference? (one would be wired in parallel the other in series)
Hope I'm not interfering.

Please interfere, we need all the help we can get. Mister @marconi had mentioned something like that a wile ago, but we didnt get to that point yet. He mentioned about low pass filter and peak detector. Now you add something new, pass through filter and band stop filter, I'll have to check what they are and how to use them.
I for one, I dont know this special things how to make and calibrate them. Though I read some articles about them, but still, I cant see the logic to them yet, because lack of experience. I will definitely try it. Thanks for the reminder and for the help.

 

[stevethesparks]

@240V it would be a band pass filter rather than a band stop filter (parallel) Sorry I had assumed 12v or so, I think I need to read the whole thread so ignore me and go with the much more informed Marconi.

 

[_q12x_]

@240V it would be a band pass filter rather than a band stop filter (parallel) Sorry I had assumed 12v or so, I think I need to read the whole thread so ignore me and go with the much more informed Marconi.

@stevethesparks The summary of this circuit is simple. Is working at 5V for all modules, for the entire board circuits. It is working perfectly on the working table. It is messed up on the wall, Near the 240V AC, 50Hz inside the wall. If I put a metal shield in the back of my board, and ground it, again, is working perfectly. BUT if I connect the relay to actually switch the 220, either by inserting the relay in the hole, or by dragging some wires from relay to the live wires in the hole socket, it is terrible messed up, again.
This is the summary.
Mister @marconi here is trying to replicate my circuit with the components he have available and also expecting some from ebay as well. In the same idea of repairing this 50hz interference.

 

[_q12x_]

Mister @marconi , talking with the guys here I was struck by an idea. I think the relay is so small and cute, that its metal contacts are reverberating through all the minimalist isolation he has in it, and travels on it's (5V) power wires, to the board, to the entire thing, bypassing the grounded metal shield and affecting the sensing circuit. It's like water, getting on a thread to the other side of the board.
Because, as I mentioned it, with the grounded metal shield in the back of the board is working perfectly. BUT if I connect the relay to actually switch the 220, THEN it is messed up. You see it how I see it?
I very much think that the relay should be shielded and filtered and protected to not transmit further the frequency. Right?