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]

Here as some simple component additions which may improve the operation of your wings circuitry - see attachment 1. The capacitor C1 - top right red bubble - is to provide some low pass filtering for frequencies above 50Hz. Try C = 0.03uF or thereabouts. At 50Hz its reactance is about 100kOhms so negligible when compared with the 11k (between the 2N2007 source and 0V) across it; at 1000Hz its reactance is 1800 Ohms so lower than the 11k across it. With increasing frequency the 11K will be bypassed.

The other thing you could do which would please me too is physically separate the mains relay from the low voltage circuitry and introduce an optocoupler - something like the circuit I have sketched in my second attachment. The 10uF across the photodiode in the optocoupler is to short out any 50Hz pick up signal appearing between the signal S and 0V. The 500uF does the same for any pick up between 0V and 5V leads to this circuit. Then put the circuit inside a plastic box with the mains going in one end and the low voltage wires into the other rather like what I did with the white oblong connector.

 

[_q12x_]

A very parallel update: Today I am happy I received my first performant oscilloscope. I am waiting for it from my past life. A lot of problems with the mail. But it finally come.
DSO138 is a digital osciloscope

I am mentioning here, because mister @marconi asked me what measurement tools I have. So this fall in that category. I have a very old and shitty osciloscope (transistorized) - it is written on it, with the most basic functions imaginable. A friend from another forum encouraged me to take this little thing as a very good upgrade for what I have, and I believe him.
Now that I have it, maybe is a game changer. But the problem is that is a tool I literally dont know how to use it yet. I understand I am not allowed to measure more than 30V with it, if im not mistaken, I have to read more specs about it. So no 220 measuring with it unfortunatly. But for the 5V on my board, it should be very good.
So from now on, consider this tool that I can use.
I also received my IR leds + black photo diodes in 1 package. 50 pairs total = a life time use.

 

[marconi]

I would love and oscilloscope but in reality I cannot justify the expenditure on one. That oscilloscope looks very interesting though- could you send me some details of it please? I think it will be helpful to you in your current and also future projects.

I will keep it brief now and will say more tomorrow morning. My prototype switch will reliably detect flat white sheets of paper presented to the two IR diodes. What I am having problems with is the presentation of the hand to operate the switch reliably. It often does work but the orientation of the hand and which part of my palm‘s skin is illuminated matters greatly. This is is not surprising really because the type of reflection from the smooth white appear is specular and generally consistent whereas when it is off a rough bumpy surface like skin it is diffuse. There is also more absorption of infra red light by skin than by white paper. All quite interesting as a further problem to overcome. My first thought is to use more than one photodiode to look at the illuminated patch of skin from other directions and then combine their signals to determine the presence and closeness of the skin on the palm of the hand. In other words an array of sensors.

Here is a short article on the subject.

Physics Tutorial: Specular vs. Diffuse Reflection - https://www.physicsclassroom.com/class/refln/Lesson-1/Specular-vs-Diffuse-Reflection

 

[_q12x_]

...That oscilloscope looks very interesting though- could you send me some details of it please? ...

Yes, no problem. I actually did my homework before buying it, looking on mister YouTube for a lot of these litle osciloscopes and then comparing prices on ebay. I spent like several months doing this thing. Ofcourse, not all the time , but sporadically. Then when my friend insisted on it, I already new a lot of them so it was a smooth push for me to give in. I suggest to you to do the same. FOr sure there are many more optiones there that will satisfy your needs. My prerogatives was cheapness. Im not sure if is the same for everybody else. With these in mind, here is my cheap'o osciloscope link:

DSO138 2.4" TFT Digital Oscilloscope Acrylic Case DIY Kit SMD Soldered New | eBay

Sampling buffer depth : 1024 bytes. Vertical Sensitivity : 10mV / Div - 5V / Div ( 1-2-5 progressive manner ). Available rising or falling edge trigger. Kits using ARM Cortex-M3 processor (STM32F103C8).

www.ebay.com

I keep a separate list on my PC for ebay purchase because they are changing with the weather. For example right now their prices changed for the same exact product:

Now is 17.88 but my deal was at 16.21. Excelent deal for me.

Without plastic case, but im building one from cardboard right now.
If you look lower in the page(scroll down) you will find Product Description, with a lot of information.
You can find at similar price if you search properly. Usually they do that, they change their name both user and product. But if you keep your eyes on the money, you will find it cheap as mine. Be careful not to buy "unsoldered ones". I emailed the guy and I was specifically tell him to send me the soldered one. Because a lot of youtubers were complaining about it, and i learn to avoid it. Youtube is your friend. Use it.
Again, I looked for the cheapest, not the quality. Just enough to do its job.

...My first thought is to use more than one photodiode to look at the illuminated patch of skin from other directions and then combine their signals to determine the presence and closeness of the skin on the palm of the hand. In other words an array of sensors....

Yes, I also suggest a RING of both, sensors and IR leds. I also recomand a high power IR led, like 1W, 3W,5W,10W. If they exist and at what price. I didnt search myself, but I will soon and update you from my side. You should give it a search as well. The ring I have in mind will have around 10x 3mm or 5mm usual leds/sensors. For the power ones, 1 will be enough.
I will update you soon with the circuit that you made for me. I just wake up now and I will start it today.

 

[_q12x_]

Im not allowed to edit my previeous answer, but I was adding this text next:​

In other words an array of sensors.

Check this out ! I was right without even searching for it, but now I searched and I find it:
LED-IR-850nm-940nm-3W-5W-10W-20W-30W-50W-100W-High-Power-Infrared
100W dude! That's what you have to buy ! Hahahaha.
Another link with the cheapest: 1W-3W-Infrared-IR-High-Power-Led

Here, 1W or 3W is the same price, so I will choose the 3W if I were you.
1$ for a 3W IR led... it's very good price. It's the cheapest I find.
And you will use the same sensor, BLACK plastic IR photo diode.

 

[marconi]

Good morning. The electronic components I ordered to copy the sensor you have used did not arrive yesterday - maybe today. Today I will play with the make up of my second IR sensor which had the wider field of view photodiode. I mentioned making an array of photodiodes. The thought occurred to me yesterday afternoon while litter-picking ( don't laugh - it is good for the mind and soul!) that I could try one centre IR photodiode and two IR LEDs above and below or left and right or all four in a quad around the photodiode.

In order to combine the signals from each photodiode we will need to construct a summer circuit. I have ordered some 741 operational amplifiers. You may wish to revise your knowledge of summer circuits using op amps:

https://www.electronics-tutorials.ws/opamp/opamp_4.html

One would have to be careful upping the power of the IR radiation because I it will increase not only the desired reflections from the hand but also everything else in the field of view of the sensor which would create a background clutter signal. The most noticeable effect of this would be to illuminate the first or first few LEDs of the the ADVM. This is not something you want to occur in your (or my) final design.

A last thought for something to test on your circuit: could you replace temporarily your 5V power supply with a 6V battery to find out to what extent the power supply is introducing mains interference?

 

[_q12x_]

Good morning.

Good morning to you as well. You should first of all read the replies I send you , and after that say your thoughts. Even if they coincide with others. Check my solution for you. You will like it.

 

[marconi]

I have indeed read your posts carefully. They contain good information and creative ideas both of which I have come to expect from you. It is pleasing to see we thinking along similar but not always the very same lines.

 

[marconi]

https://www.mouser.co.uk/datasheet/2/427/bpv23nf-1766846.pdf

The idea of using a black photodiode is very clever. I wish I had thought of that but I was not aware of them. Thank you for teaching me something.

 

[_q12x_]

https://www.mouser.co.uk/datasheet/2/427/bpv23nf-1766846.pdf

The idea of using a black photodiode is very clever. I wish I had thought of that but I was not aware of them. Thank you for teaching me something.

Im not that masterful with the IR lights also. But I know how to search.
This is what I bought and the package arrived already yesterday. The black ones are the sensors and the transparent ones are the leds.

So my 1W/3W IR led is not such a good idea for you and your tests. You still didnt read all my messages from before. I think this more powerful led will resolve your problems. And also the ring(s) alternative I mentioned. But you do what you can do.

 

[marconi]

Good morning. I have reached a point where the IR hand proximity sensor works smoothly, reliably and without any false switch ons or switch offs. I constructed an IR sensor as in the diagram in my #96; a centre photodiode with an IR LED torch to the left and to the right of it; this arrangement increases the illumination of a small patch of skin on the plam of the hand which the photodiode looks at and increases the intensity of IR light entering the photodiode from diffuse reflection off the skin. The LEDs are angled in slightly towards the photodiode. I will post a picture of it later today. It was not very bright yesterday so the ambient light level in my shed was low; with the shed lights on the first LED of the column of eight sometimes illuminated but this is far too low a Vs signal to turn the lamp on or off.

Now that I am happy with my circuitry I will draw out in later posts some diagrams, each diagram covering one or a number of sub-systems eg: power supply, ADVM, Three level/step detector.....

The electronic components to attempt your original sensor arrived yesterday. I will turn to trying to sense the proximity and closeness of the palm on a hand in a similar way you did - a more difficult way in practice to achieve the same level of smoothness, reliability and low false activation. since it is a passive- passive type sensor there is more variability in the signals the body picks up and the sensor then attempts to pick up.

Regards

Marconi

 

[marconi]

TRIO IR SENSOR:

npn transistor BC547B

850nm IR LEDs ( x 2) with 40 degrees field of view between half power points:

https://static.rapidonline.com/pdf/58-0114_v1.pdf

850nm IR photodiode (Unfiltered) with 15 degrees field of view between half power points:

https://static.rapidonline.com/pdf/58-0470.pdf

I actually used 2 x 22uF in parallel because I did not have a 47uF.

Vs is the signal output which you could feed into your LM3914 pin 5.

I will post a picture of the sensor in the next message.

 

[marconi]

MP4 video later today.

 

[marconi]

Stabilised 5V 2A power supply. ST78SO5CV is T220 type and a finned heat sink attached to it like this:

https://static.rapidonline.com/pdf/36-0250.pdf

 

[marconi]

https://www.ti.com/lit/ds/symlink/lm339.pdf?ts=1612308491496&ref_url=https%3A%2F%2Fwww.google.com%2F

I used two quad comparator chips LM339N. Nine 2.2kOhms resistors across 0 to 5V rails. First comparator connects at point A and the eighth at point B. The signal Vs to drive the eight LEDs is input to all the - inputs of the comparators.

The comparators sink the 8 yellow LEDs to turn them on so the voltage ladder ( the Vref points along the 2.2k potential divider) must feed into the + inputs of the comparators. Then when Vs > Vref the comparator output is 0V and when Vs< Vref the output is 5V.