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]

I already have the op amps:

https://www.ti.com/lit/ds/symlink/ne5532.pdf?ts=1613649008909&ref_url=https%3A%2F%2Fwww.ti.com%2Fproduct%2FNE5532

These are the multi-turn trimmer pots:

https://static.rapidonline.com/pdf/71494.pdf

 

[_q12x_]

I just open your .doc file and wow, you have some there.
But i dont see the IC. Or the IC you have already and you bought supplementary components. I think that might be it.
Do you have lm3914? I can send you one of mine. I have 10 brand new. Well, 2 of them are tested a lot and 1 in use. But I can send you a new one if you dont have.
Or you are using your NE5532 Ic('s) for teaching-learning purposes? Or maybe for more interesting qualities they may have, than my lm3914? I am guessing here your reasons, since I could not understand you perfectly.
I also see in your list 2 regulators for 12V. I used for 5V. I know there are inverse voltage regulators but I never bought them. (for -VsxV -5V or -12V for ex).
Thanks for sharing your components !

 

[marconi]

A progress report in pictures. Non-linear response with respect to proximity at the moment. First detection at 30cm. The voltmeter is showing Vs.

 

[_q12x_]

Excellent presentation through images ! Very good !
Yes I see the DMM values rising with close range. That piece of paper is highly reflective. I would use a black or dark grey mate surface to more accurately simulate the hand. Or actually the hand. But is a good progress so far.
Damn, that looks complicated as hell there on your table. It shows you had some good time with it. Haha.
What next?

 

[marconi]

q12x: Today I added 8 LEDs to the ruler each driven by a comparator. Each comparator has the same Vs input but also has its own unique reference voltage Vref derived from one of 8 trimmer potentiometers. This is a second prototype project which uses a 12, 0, -15 V supply to increase the dynamic range of the voltage Vs from 0 to 4V to 0 to 12V as a hand is moved from 30cm away towards the sensor. The use of 8 trimmer pots to provide the 8 reference voltages should allow me to cause the LEDs to illuminate in equal distance steps As the hand approaches the sensor. Not yet calibrated - work for tomorrow.

From left to right the board has: two linear voltage regulators and heat sinks with two LEDs; Pot to produce Vs; 8 Vref pots; two quad comparator ics; one dual op amp acting as summer and inverter.

 

[_q12x_]

The use of 8 trimmer pots to provide the 8 reference voltages should allow me to cause the LEDs to illuminate in equal distance steps As the hand approaches the sensor. Not yet calibrated - work for tomorrow.

Very interesting indeed - I want to see how had you think it. Make me a circuit diagram please.
I know is boring to draw, but you must do it for me because i find it very interesting.

 

[marconi]

Of course I will draw for you. It will not be tonight though.

 

[_q12x_]

Of course I will draw for you. It will not be tonight though.

When you have time of course and thank you ! I have a couple of uA741 opamps, and I am thinking to reproduce your circuit that you just built. I know, I should buy more newer opamps but these I already got in considerable number so why not use them. I will learn about opamps a bit more in this way. I think you just made a very cool project right now. And Ive also mentioned using opamps at some point, for the scm and yours here is just my wish come thru.

 

[_q12x_]

How is the drawing and the pot calibration going, mister @marconi ?
If I will manage to built it after your draw, I might assist you. Haha, jocking of course, since im not that good with opamps.

 

[marconi]

I have had a frustrating day. I bought some pre-wired jumper leads in different colours and lengths. I have discovered that some of them have no continuity between ends and others only intermittent continuity. Even the ones which do have reliable continuity do not make a reliable connection in the contact holes of the breadboards I use. I will go back to using solid bell wire which I have never had any problems with ( illustrated below the yellow jumper lead).

So not much progress today because I have had to track down defective leads and connections. I will draw op amp circuits tomorrow.

 

[marconi]

Are you about to start work on an infra red sensor circuit module like me?

741 are good and reliable. You can use them as comparators. You can use them as voltage summers, amplifiers and inverters and for many other useful circuits.

Operating an op amp using a 0 to 5V single sided supply is very limiting. How do you plan to produce a double sided supply of at least 12, 0, -12V? My second prototype is using 12, 0, -15V supplies and 0, 5V for the logic circuitry. The 741 can operate on +/- 22V but the recommended upper limits are +/-18V.

The higher supply voltage enables more Volts per mm from the sensor which in turn increases the voltage steps between each Vref for each comparator and led.

Once I have a way of adjusting the Vref for each red led on my ruler I plan to experiment with a few led/photodiode arrays to see how closely they meet your requirement. You have seen a picture of the first one already.

 

[_q12x_]

Thank you for your response my friend mister @marconi.
I had numerous problems with my breadboard contacts and wires as well. I do not have the money for fancy wires like yours. I made some multiwires wire like you have, using simple scrap wires, pins from dead components, especially leds, which have that nice square leg profile, solder and heatshrink rubber. I build 2 black and 2 red like that for more than 5 years and I had using them extensively. Never broke ! I also have a kit of pre-bended solid wires for breadboards, in which I trust very much, but is a bit harder to use them on too much agglomerated circuits. Because these limitations, I learned to build on modules. You heard of them? Haha. Me and my humor, ei?

I got surprised I can not find the exact model colors I have. These are very diferent color coded. I think mine are prettier. Or I am just simply too used to them. But this type of wires I use. Very secure very robust. The breadboard is giving signs of unsure connections in some specific spots that i didnt find yet. I put some larger diameter wire for sure and that widened the little clamp inside some holes. But is a little percentage damaged and I can live with it though I have an eye on it all the time when something goes south and it shouldn't.
I didnt do much as well. I just happily use it. Im telling to myself this is a usage test so... it already passed probably 1 week of usage the entire board. And is working more than fine. Excellent. I'll have to play with the remote control for the next module. That part is easy since I have some already made modules from mister ebay. I will try them first and if something goes south, ill go into more experimental remotes. I hope not.
Now...I have a quest for you. It is purely a... design problem. Or connection problem. I want to hear a "tick" from a 5V buzzer. There are 2 types and I have both. The passive ad active buzzers. I was stupid to take the passive ones first and then discovered the active ones existed. But now Im thinking to add a tick sound for each 1-10 pin activation and using a passive buzzer that only make a "tick" when is getting voltage on it. Is how I am planning at this point but I must make tests. Maybe the active buzzers are the solution. We will see. SO your quest is to tell me how you will link another 10 wires on the already finished board as it is. Draw on top of it or just explain, just make me understand your solution. So, understand me well, im asking you not the circuit how should be, but the wiring. Because if the wiring goes to hell, and becomes too complicated, then I will not build anything about sound, indiferent of how much I would love to hear it. This is plan A. If plan A succeeds, plan B is to create, built and test the sound circuit.
Thank you for your understanding and help, mister @marconi .

 

[marconi]

Here are two circuit diagrams. The quad comparator ics I used can only sink an output to -15V. This is what the drawing top right of the second attachment is attempting to show.

The summer circuit sums the Vsx inputs but also inverts. So if the Vsx inputs where 1, 2, 2, 4V the output would be -9V. The unity gain inverter changes the -9V to +9V.

One has to be careful not to saturate the output of the op amps ie: the output must swing between +10V and -13V if they are supplied by +12, 0, -15V rails. Probably could go closer but I like margins in this case of 2V.

The VR1 pot on the summer is to adjust the peak output of the summer so it does not saturate nor send a signal to the inverter which would saturate it.

I made a mistake in ordering the voltage regulators because I meant to buy a +15V positive regulator but clicked on +12V. This explains why why comparators are operating using a negative going signal because the -15V side of the supply gives me a wider voltage range ie 0 to -13V whereas the other side only provides 0 to +10V.

The 741 has a complementary pair of output transistors and so can sink to the negative rail or source to the positive rail. Worth studying the data sheet for a 741 and to note the tips on circuit layout.

https://www.ti.com/lit/ds/symlink/ua741.pdf

The 741 can be used a a comparator and its output can drive directly a small led (via a series resistor to limit the diode current.). Thus with several 741s and a trimmer pot providing a Vref to each you can produce something similar to me. Also provide a test pot to generate a Vs to confirm you comparators light their LEDs dependent on the Vs and Vref.

I hope this helps.

 

[marconi]

I will reply to your #207 later when I have time to read it carefully. I have to go out now.

 

[_q12x_]

Thank you very much for your circuit drawing ! I know it was hard to make it. There are some little notations that I am not used to, but I think I figure them out already. I read all your text very carefully and also read both schematics. So far, i can't say anything, but I will say a lot after I built it. Unfortunately I only have 5V power supplies. (7V I just look from the transformer). Hmmm, from my earlier tests I know the 741 is capable of working in 0-5V quite fine. Ofcourse I am not that efficient with opamps. I hope 5V will not be a problem. If it is, then I will try to find another higher power supply. Until then, I will use what I have. Thats all I can say until now.
Referring to your 12V regulators mistake instead of 15V, I think it is possible to create a custom regulator from components at what value we desire and how strong we want it to be. Hopefully. But this is another project to make with opamps that is put in plan/future to make. I think is a very interesting project.

For your practical reasons, I think your project is complicated enough and my solution here will complicate it even more than it is , so ignore it if you think is too much, and take it as a possible/alternative solution when in need, like you are now. My google search input is "build a regulator using an op-amp" and I switch to images to get a plethora of similar circuits like the example I put here.