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 !

 

[marconi]

Thank you for your reply which I will read carefully tomorrow morning when I get up. Two of the nurses who attend my wife are Romanian. They are very professional and have kind happy personalities which are essential since they are in our home for 6 hours each day. So, helping you and your country will be some payback for that. They will be amused to know I am in contact with you.

I am cooking at the moment so I have to sign off for today. I will write again tomorrow.

 

[marconi]

I have now read your note to me twice and I understand what you have said very clearly. Yes - I have come along as a 'clever dick' 'know-all' and you are nervous about making changes to your design and its construction because you have spent 7 months working on it. I suggest - so tell me if you agree - we do some simple tests on your circuitry first. They will involve disconnecting some wires but not dismantling any of the components. Depending on what we find you can then decide to make some changes or not. It would be really helpful to know if you have a digital or analogue multimeter so that we can take some voltage measurements.

To save time and assuming you agree to the approach I just mentioned please measure these voltages for me with respect to the 0V rail:

1. With all circuitry disconnected from 5V power supply the output voltage of this supply;
2a Now reconnect the circuitry. What is the supply voltage when all the LEDs and relays are off?
2b. What is the supply voltage when all the LEDs and relays are on?

Now disconnect the wire at pin 5 of the LM3914 which comes from the sensing circuit.

3. Using a short piece of wire - a jumper - connect pin 5 to 0V - all the LEDs should turn off - make solid connection do not just hold the wire;
4. Now move the jumper to connect pin 5 to the 5V rail - all the LEDs should turn on;
5. Make a potential divider from two resistors R1 and R2 say 10K and 10K and wire this across the 0 and 5V rails. If you have a small value capacitor - a few uF - please wire it across the resistor R2 which connects to the 0V rail. Connect pin 5 to the point the two resistors join together - approximately half the LEDS should light;
6. Now remove the resistor R1 which connects to the 5V rail so that there is only one resistor which connects pin 5 to 0V - all the LEDs should be off. Take a jumper wire and connect one end to the 5V rail. If your circuit (apart from the sensing circuit) is working as you want it to, if you repeatedly connect pin 5 to the 5V rail the LEDs should all turn on when raise pin 5 to 5V. If you repeatedly touch and then untouch pin 5 and touch and then untouch the LEDS should turn on and off and the relays should be turning on and off - toggling - as you want them to do - to eventually turn your room light on and off everytime the wings are illuminated. Everytime you touch pin 5 to 5V the capacitor will charge up - when you untouch 5V rail the capacitor will discharge through R2 - allow a little time for this to happen.

This is probably enough for now. Please let me know how what happens.

Regards

Marconi

 

[marconi]

So far I have watched Led Wings Projekt 1, 2 3 and 4.

 

[stevethesparks]

Fair play to you Marconi. You have gone way beyond the standard reply, and continue to do so. Interesting as well. ?

 

[_q12x_]

So far I have watched Led Wings Projekt 1, 2 3 and 4.

Thank you... as i mentioned, it's a lot of talking, it's probably better to move forward faster by scrolling.
I am just starting your experiments right now.
But pay attention to 1 very important thing. The circuit does work excellent when is on the workbench !
It only gets wierd on the wall, in the very close vecinity of the 50Hz. So your experiments are on a working circuit ! Ok?
I should probably mention this little detail as well, on the breadboard it worked in a way, after I assembled it on my modules boards, it worked totally different (it was my iron table that was ungrounded at that time) but still a big difference. Its because the breadboard have in it a lot of wires as well. So those were sensitizing the circuit. I was not aware at that time, I figure it out in time, after. Right now on the table I am working I have live wires but is a respectable distance, like 40cm to them from my circuit. But on the wall... is close as 5cm to working live wires, not standby ones.
Your experiments I presume, are to be taken on my workbench and not on the wall. The thing is on the wall, I have to keep everything in equilibrium, and is not optimal to work there, but is more advisable to do it there, I am aware.
After I will make your experiments, I plan to take out the sensing circuit module and mount the board on the wall, and make direct simple contact, without the sensing circuit involved. If everything goes to hell, then Im screwed. If everything works fine, then I will proceed to make another sensing circuit, with diferent technology (no field effect transistors). I am thinking on something capacitive like theremin circuit, I was suggested in another forum, not entirely my idea, but I love it. I already looked over those types of circuits and they are a bit complicated, but I put in my mind to try one, even if is a bit too complicated from my original plan.
But first, the experiments.
About multimeters, I have probably 6. One I use it exclusivly as ampmeter. I even managed in my youth to find an osciloscope but is so old and shitty... its a "transistorized osciloscope", is written on it. I dont use it though, i admit.

 

[_q12x_]

@marconi I made a part of your tests.
For 2a and 2b, the voltage is 5V everywhere. Im not sure what voltage are you reffering to measure. Instead, I measured circuit current, that is shown in my PSU (PowerSupplyUnit). When all is Off, is measuring 20mA. When all is On, is 60mA. But when I keep my hand over the sensing circuit to really keep everything ON including relay1, it goes to 100mA, and after I raise my hand, it goes back to 60mA.
2C- disconnect pin5. At this stage, pin1 and pin10 are ON. It should not stay on. Sign that the IC is damaged. Then I thought maybe is interfering with the other modules, so I disconected signal amplifier module, that also automatically disconected S (signal) track to the relays. So I have powered only the IC and the leds.
With pin5 in air, led1 and led10 is on.
But... If I keep with my hand a piece of metal wire on pin 5, unconected to anything, like an antena, all the leds are turned on but very dimmed.
If I connect pin5 to 0v, everything goes off - that is good.
If I connect pin5 to 5V,only pin1 is ON.
I remember in my breadboard experiments, it got me the same results (pin 1 was not litting back then), but pin5 was behaving as right now. I also tested back then with another IC and the same result. I can test it on the breadboard with a new IC and see how it will work, if is the same as now with this one here.
I also observed a slight current through all the leds, with pin5 in air, when I move my hand and body around. It is still interfering with the sensing circuit I guess. Very very strange.

 

[marconi]

I have now watched 5 and 6. Only when I have watched all your video clips will I reply.

I have some 2N7002 making there way to me in the post for me to replicate your sensing circuit ?.

What a wonderful experimenter you are!

 

[_q12x_]

I have now watched 5 and 6. Only when I have watched all your video clips will I reply.

I have some 2N7002 making there way to me in the post for me to replicate your sensing circuit ?.

What a wonderful experimenter you are!

I am very pleased you like it, really, but im a bit... sick of it. So many failures, one after another, literally. Please read my last reply, I put some modifications in it. My biggest problem is that I used the cardboard, and that is gathering some elecrostatic charge on it, i am aware, but i trade it for the maneuvrability and manufacturing ease I can achieve with it. Also very fast experimentation as you already are fascinated by it. Heh. It works for a large majority of circuits, but with this kind of sensing circuits, i suppose I push the limits with it. Eh well, I tried, right?

 

[_q12x_]

I am not allowed to edit my previous posts? What an imbecility.
I just tested on the breadboard the same circuit for LM3914. And I got the exact same results as with my mounted IC, except the led1 and 10 are staying off when pin5 is in air. That is the only fault I have on my board, and I bet it is some sort of interference for those leds/pins.
Pin5 on 0V, nothing happens, all leds are off.
Pin5 on 5V, again, nothing happens, all leds are off.
But, when pin5 is in air, and touch it with my hand, some leds are on, but barely, very dim.

 

[marconi]

I cannot spend much more time tonight because I am starting to cook. I would appreciate it very much if you did what I asked in my post from first thing this morning in order to establish which sub-systems do indeed function as desired. I suggested we first checked that everything from pin 5 to of LM3914 to the relay which switched the room lamp was operating as you wanted it to. If it does then we concentrate on the sensing circuit.

But it may well be that the sub-systems I have asked you to check are also subject to interference or disturbances which disrupts their reliable function.

To give you some idea of one of my lines of investigation you have 50 leds each of which consumes between 10 and 20mA say or in total between 0.5 and 1 Amp. The PURE power supply you showed in one of your YouTube clips outputs 5.5V and its rated output current is 1A. What current is required to operate the two relays which is extra to that for the leds? How well regulated or stable is the pure ‘s voltage output as the current supplied approaches its rated value - at the moment neither you or I know. Why does the voltage output of the pure matter? Because it may be affecting the operation of the sensing circuit.............

 

[_q12x_]

I've updated the original sketch circuit. I discovered a little error there so I redrawn it all, I had it in plan to do it, so now I did it. The error was those 2 resistors how they linked to the pins. Now is corrected and is exactly as in my real circuit. If you want to make it like mine.

You can check it here: Q20201219 Led Wings Projekt Circuit by q12a on DeviantArt - https://www.deviantart.com/q12a/art/Q20201219-Led-Wings-Projekt-Circuit-864540519 Is the same link as before but I changed the image with this updated version.

 

[_q12x_]

another update:
I made a test for the LM3914, then I made a new test on the workbench and on the wall.
I made a manual switching module with a pot and is working fine.
I was afraid of further interference on the wall, but is normal now with the pot.
I am curious what other sensing modules you can think I should try.
Please enumerate all that you have in mind. I have already mentioned myself a few, in the movie. I don't care for originality but I care for quantity this time. So, go nuts.
Warning, this is a lengthy movie, 23m.

 

[marconi]

Buna dimineata. Greetings from London. Your youTube clip was very clear and confirms all is well when the sensing circuit is disconnected - but I await confirmation that it continues to work 'perfectly' when you remove the metal back-plate - an important check.

You have also confirmed your circuit only draws about 60mA. Does this figure include the current for the two relays? Perhaps you could just tell me the resistance of the coils of these relays and I will work out how much current they draw?

When pin 5 of the LM3914 is not connected to anything it will be at an indeterminate or floating potential with respect to ground - or in other words a random voltage - because there are leakage currents to pin 5 from within the integrated circuit. In electronic circuits one must ensure that input pins are never left floating because such an electrical input is random and will affect how the circuit works. We connect them to 0V or 5V.(VDD/VCC).

LED1 is so bright compared to LEDs 2 to 10 because the LED current is set by resistor R1 and R2 at pin 7 - see figure 1 of the datasheet which says the LED current is 12.5/R1. Pin 1 only has one LED connected to it whereas the others have three LEDs; thus LEDs 2-10 have a third of the current flowing through them of LED1. We can adjust the brightness of LED1 to match that to LEDs 2-10 by adding a suitable resistor in series with it - you can work out what resistance value is required or I can help you with that.

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

I must express some mild irritation with you. I have asked several times if you would check that the leads of the MOSFET 2N7002 are actually connected correctly in the sensing circuit. It should be connected as in my attached diagram. If it is wired in wrongly that could explain why in one of your youtube clips the potentiometer had no effect on the performance of the sensor circuit.

I will construct your sensing circuit to see how it performs. We can work together to see if we can make it work reliably. If we cannot I have a sensor idea which uses infra red reflection of the hand. My components for your sensor and mine were ordered last Saturday so they should arrive soon.

Regards

Marconi

 

[_q12x_]

Buna dimineata de asemeni. Your romanian is perfect. Good morning from Romania as well. I didn't slept all night, and now im a bit tired.
I am happy you watched that last video and seen the updates so far.
I already explained the relay part:
"When all is Off, is measuring 20mA. When all is On, is 60mA. But when I keep my hand over the sensing circuit to really keep everything ON including relay1, it goes to 100mA, and after I raise my hand, it goes back to 60mA."
I also have the data about the relays, no need for calculations. Works at 5V, draws 30-40mA, and coil resistance is 128R. But in my wings circuit they draw around 30mA. Im not sure why... probably they are limited by the transistors in the relay driver circuit(the little ones with orange and blue leds on them). Is my best guess.

In electronic circuits one must ensure that input pins are never left floating because such an electrical input is random and will affect how the circuit works. We connect them to 0V or 5V.(VDD/VCC).

That is a very interesting piece of information. It is true for PIC's as well? where you have many inputs/outputs pins? The effect is only visible when I touch pin5 on lm3914, and not when is free "in the air' as I call it. But I get your point, to avoid stupid contacts of any kinds, you link it to a rail. Im not sure is a general truth, but it might be fine for many IC's.

Led 1 and 10 are the least of my concerns at this point. They will be dealt with in the very end. As you probably feel me and observed me, I dont like to do simple things, but the complex ones that I am attracted. So, in my mind, I must clear the general fog and then smell the flowers.

Yes 2n7002 is mounted correctly. I pay special attention and double check when I mount my transistors. Im also very careful for a very simple reason: I don't like to make the circuit again from scratch. So im careful from the start.

I must also share this old sketch of mine:

It means the area of effect of the sensor, how I imagine it should work. That is a crude representation, but it tells the idea well. Of course I want gradual opening of the leds, and also a considerable distance. Ideally the distance to be customized. That is done from the antena alone, from my discoveries so far, with this sensing circuit in particular.
As I said in the movie, I will use IR for a remote control. So I will not interfere it with my sensor. Or should I? If I am making an IR sensing sensor? But as how much -------- I got from this sensing circuit, the IR one should be easy in comparison. I already have a very interesting module I will most probably use. At least I will test it first then I will consider to use. We'll see. I'll wait for your ideas first.
Thank you for your reply. Have a nice day, today.

 

[marconi]

The reason why you have an increasingly small distance between illumination of the LEDs as the hand approaches the sensor is that the sensor has a variation in voltage output (V5) with d as I have shown in my first diagram. However, the LM3914 has a linear relationship between V5 and LED illumination interval because all the voltage steps along the resistor ladder (the 3 resistors R across the 3Volts Zener diode) to the comparators (second image) are the same - 1V in my example.

I could not buy LM3914 ics so I have bought discrete comparator chips which means I can adjust the voltages to each of them to correct for the Voltage/distance output of the sensor circuit to achieve the 'customisation' of wing illumination you mentioned in one of your earlier youtube clips.