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]

[My response is written black bold to items marked up in red - I am not shouting which is often the way bold is interpreted!]

So this is your definitive solution? The IR ? No. In my report (#162) at para 7 I wrote that 'I demonstrated an IR sensor which at least showed it had some potential to meet your requirements in paragraph 1'.

In earlier parts of our discussion we mentioned the use of arrays of opto-diodes to make a sensor which achieved the performance necessary to provide a dome-like sensing region. My SCM Mk3 is just an examplar of an element of such an array. There are of course many other ways of making the elements. Whatever elements are made their outputs will need to be combined - summed - to produce a signal Vs which is related to anything moving in the array's field of view. What can envisage the dome being constructed from many cones where each cone has one element or a patch of elements in an array.

Your light bean switch does not use the same optical mechanism for the detection of the hand - it relies on the sensor either seeing or not seeing the light emitted from the LED. The beam has to be blocked off from shining on the photodiode receiver to indicate the presence of the hand - Vs is a binary 1 or 0 output. In my IR sensors the light is reflected off the skin of the hand back to the photodiode - the amplitude of the reflected signal is indicative of the distance away. There is a threshold voltage Vt in the detection circuit. If Vs < Vt it is deemed the hand is not present but if Vs > Vt it is deemed the hand is present.

Your latest SCM is a completely different sensing technique which I do not need to explain again. It does not use the same principle; it uses electrostatic or if your prefer capacitive coupling between the antenna and the very high resistance input of the MOSFET to detect very small current flows between the hand and antenna. The problem with this technique is that the detection relies on very high sensitivity sensor because the current are so small - 10 to 100 microAmps. This makes it prone to a range of disturbances as I attempted to illustrate in my #161.

The current construction of your wings, the distributed layout, the exposed circuits and interconnecting wiring and proximity to relatively much much higher sources of potential lie the 220V ac mains - all combine to make it nearly impossible to avoid interference which causes random and unreliable functioning and as you have discovered damage to the MOSFET. Theoretically it is not impossible to use the technique of your SCM but you would have to re-start COMPLETELY your project to construct and interconnect the modules with a layout which minimises or avoid mains pick up and this includes the use of screened boxes and wires etcetera. This is why I reckoned you would prefer to 'bank' what works, dispense with what does not and tackle specifically a challenge to make a sensor using different techniques/technology. It is of course up to you what yo do. I have I hope been careful to explain my reasoning.


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? Yes - without any further comment.

 

[marconi]

My early thoughts on my way ahead. I am working over in my mind a dome shaped array of IR LEDs and photodiodes mounted on the surface of a tennis ball cut in half. I want to use the components I have bought already so I need to plan how best to arrange the LED illuminators and photodiode receivers using what I have remaining.

Don't expect anything from me for at least a few days unless I am fortunate (unlikely) at first attempt.

 

[_q12x_]

My number 1 concern is not really the shape, but the range. And also the rezolution, meaning, that it can sense clear enough the object in front of it. If you can concentrate on the range, and make it big to very big, that will be a significative achievement.
I mean, the shape is easy enough to be achieve.
Im also thinking on the theremin in this time. That is a hard son of a bici circuit. I didnt start it yet. I am thinking to the most elementary/basic theremin circuit. I already find something but involves some IC's that i dont have. I have to take everything I have (I have a bunch or random IC's) and check what they are and what they do. Its a lot of work.
Im also thinking on some already made sensors circuits like PIR - like this one: 220V PIR but I dont know how tweakable it is, to calibrate it to exactly my desired distance and to be liniar. There are too many unknowns about it, but is an idea.

 

[marconi]

I have my ‘starting orders’ then - to concentrate on range not dome coverage.

On Theremin - may I suggest you think hard on the physical mechanisms which this circuit relies on to control pitch and volume? And then think about what the circuit design assumes about the environment in which it operates. And then consider the environment you wish it to operate in.

My next ‘clever dick’ piece of advice is to study how the 220V ac pir motion detector switch works; what is the physics and electronics it uses to detect and decide whether to switch on or off? Also, be aware that some pirs are so-called dual technology: you can look up for yourself what that means.

Having said all the above it is a creative idea to adapt something for your purposes which is an indication of your skill as an innovator.

ps: my wife bought me an iPad for Christmas and I am still getting use to the screen keyboard. Up to now I have used mechanical keyboards upon which I make far fewer typing wrrrors - see what I mean.

ps2: another motivating poster to put up over your bench.

 

[_q12x_]

I have my ‘starting orders’ then - to concentrate on range not dome coverage.

Excellent and good luck. I expect good news ! Think on both if is easyer to you, but dont get too much distracted on the shape of the thing.

 

[marconi]

Good evening. Our gas boiler broke down so I have to heat the house and water and power all else too with electricity when the temperature outside was sub-zero Celsius. My wife has poor health so I cannot skimp on keeping her warm. Average power consumption 9kW with peaks at 11kW. So I could not sensibly heat my shed as well as the house - another 2.5kW.

I spent some time planning the opto ir array sensor Inside in the expensive warm. Here is an image of my early thoughts. Note the wider field of view ir LED illuminators are slightly in front of the narrower fov ir photodiodes Which I think would be advantageous to reduce immediate sensing of short path ir rays by the pphotodiode. A work in progress......

 

[_q12x_]

We live in appartment, but we have a hearth at the base of a chimney and is working on burning wood or coal and we are using it even now. My father is managing it. I suggest you should use one as well. It's very practical. There are portable radiators to buy. Or, if you have some nicheline around, you can make a communist old school radiator with it that will heat up very well but will consume very much.
I think that fiberglass board with 10 connectors on it, is your new testing circuit board. Correct?

 

[marconi]

Yes 10 tag board is to build the array on. My morning’s work is in the attachments.

 

[DPG]

It's a long time since I've used tagstrip!!

 

[_q12x_]

What is this board called? At what is used for originally? I suppose you adapted it from something. My best guess is from telephones. It is looking nice so far. I'll be more impressed to see your palm at a distance of 20cm or more activating it. Good job so far.

 

[DPG]

What is this board called? At what is used for originally? I suppose you adapted it from something. My best guess is from telephones. It is looking nice so far. I'll be more impressed to see your palm at a distance of 20cm or more activating it. Good job so far.

Tagstrip, or tagboard in this case, was a common method of constructing circuits many years ago before PCBs took over. It was more suited to the larger components of yesteryear and you will see it in old valve amplifiers, televisions, etc.

 

[marconi]

My plan for tomorrow is to test the Vsx outputs at the emitter of each of the four transistors where x : { 1, 2 , 3, 4} to check each quadrant of the array produces an output voltage inversely proportional to distance and of a similar value.

Then to build a four input summer op amp circuit to combine the detections of each photodiode to produce a composite Vs signal which drives the LEDs - my yellow column or your wings.

 

[_q12x_]

Tagstrip, or tagboard in this case, was a common method of constructing circuits many years ago before PCBs took over. It was more suited to the larger components of yesteryear and you will see it in old valve amplifiers, televisions, etc.

thanks, very interesting prototyping board indeed.

 

[_q12x_]

Ive also updated my artpage so if you refresh it now it should show the latest circuit I used and modifications.

 

[marconi]

https://static.rapidonline.com/pdf/82-0782.pdf

This is the operational amplifier I have chosen to be the heart of the summer circuit. It has a voltage operating range of +/- 1V to +/- 8V and a voltage swing from V+ to V-. The other feature I liked was the output can be nulled (see Offset Nulling paragraph and also Figure 7). It is also a robust ic.

The summer will be non-inverting as in the attachment. Vo is my Vs; V1, V2, V3 etcetera are my Vs1, Vs2, Vs3 and Vs4 from the photodiodes.

PS: I note I have written this while you have been posting an update. I shall make myself another coffee and enjoy reading your news.