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]

https://www.electronics-tutorials.ws/waveforms/555_timer.html

At the Rx rewire the 555 to be a negative pulse triggered mono stable timer. An example is shown in the link above.

At the moment the output of the Rx when fed in to the diode resistor capacitor network produces a positive going pulse ie on button press it goes 0 to 5V when the remote control button is pressed. You need to invert this signal so that it is a negative going pulse ie 5 to 0V.

If you insert an npn transistor in common emitter mode between the output of the diode capacitor resistor network and pin 2 of the 555 this will be achieved. The collector load is say a 10k resistor. To limit the base to emitter current put say a 10k resistor in series with the lead from the capacitor to the base. Pin 2 is connected to the collector. When the transistor is off the collector and pin 2 will be pulled up to 5V. When the transistor turns on it will be pulled down to 0V.

you may need to adjust the resistor and capacitor values so that you obtain a waveform like the red one I drew earlier at the output of the didodecapres network. When you press the remote you want the cap to charge up to 5V and stay at this voltage until the button is releasEd. Check this using you scope. You don.t want to see much ripple.

Ripple Voltage in Rectifiers - Instrumentation Tools - https://instrumentationtools.com/ripple-voltage-rectifiers/

 

[_q12x_]

hello mister @marconi and good evening.
Thank you for your help! Can you possibly join me on skype for a momment? I have some stuff i cant put online. And also we can verbally communicate. Here is my id on skype: totoq12 and I have the same robot face there as here on this website, very easy to recognize me.

 

[_q12x_]

Thank you for joining me, listening , advising and helping ! You are a very good friend.

 

[marconi]

A quick sketch of what we discussed. As a first step make this 555 circuit but leave it disconnected from pin 5 of LM3914. Connect your scope to pin3 and observe what waveform is produced and then observe the waveform across C2 each time you operate the remote push button. You may need to adjust R3 and C3 to minimise ripple. The on period ie t1 is determined by R1 and C1.

 

[marconi]

The idea behind this Rx end monostable circuit is that it causes your wings to illuminate inwards to outwards and then extinguish outwards to inwards after only one short duration press of the remote control button. There is no need to hold the remote button down for long. All the remote control is doing is triggering the monostable into action.

 

[marconi]

Small formula error for t2 corrected in attachment below.

 

[_q12x_]

ok, I copied the circuit on my piece of paper right now and I notice there is no value for any components, except that 10K in the collector.
Can you be so kind and put there some values for those components please?

 

[_q12x_]

I just google around and I remember you told me some values are from the other circuit, and I put these values. This is looking good so far?

 

[marconi]

I have just constructed the 555 Rx monostable circuit and connected to my first prototype in which the column of 8 yellow leds represents the leds of your wings. This circuit is on the right in the video and the right hand red led indicates the received and elongated pulse from the Tx.

On the left hand side is a 555 astable which produces a pulse output at a frequency of about 5-10Hz. It represents the output from the data pin of the Rex when the Tx button is pressed briefly. You can see its red led flicker on and off when I press and the release briefly a push button which turns this circuit on and off. The pulsed output is fed into the diode-resistor-capacitor circuit you have already constructed. The voltage across the capacitor connects to the base of the npn transistor which switches pin 2 of the Rx 555 between 5 - 0 -5 V to produce the negative going trigger pulse to initiate a monostable cycle.
Pin 3 of the Rx 555 is fed to a series CR circuit. The voltage across the Capacitor is Vs which feeds into the comparators which drive the 8 leds.

It works then at least on my bench.

?
ps I could not read R4 in the video So I used 10k. I see in your last post you used 47k. I will do the same.

 

[marconi]

R2 and C1 will make t1 about 1 second. You may wish to make this time constant longer. For the testing phase it is rather too short to check operation. I suggest you increase R2 or C1 by a factor of 5 so the pulse output from the monostable is about 5 seconds.

t2 determined by R3 and C3 is a time constant of about 220 x 10exp-6 seconds which is very short. If t1 is about 5 seconds you want t2 to be about 2 to 3 seconds. Easiest thing is to increase R3 or C3. A bit of trial and error until you have a t1 you are happy with and t2 < t1. Assume t2 = R3 x C3 seconds and then adjust until you have achieved t2 < t1.

The idea is for a brief burst of pulses from the Tx to trigger the Rx monostable. This way you conserve the life of the batteries in the Tx.

 

[marconi]

Do ask if there is anything you do not understand. For me, your project is more about an opportunity for me to help you to learn more about the art of electronics.

 

[marconi]

My component values shown in green in the attachment.

I will work on a circuit to combine the rf and proximity signals for input to pin 5 of lm3914.

 

[_q12x_]

Sorry for not responding straight away. My bad. But I was already in a parallel project. I started it in the night before talking with you. I interrupted it while talking to you, and then I got back to it immediate after that.
It was a necessity project. I had that problem when you have only 1 good power supply but 2 tools to be powered from it. So I made this board that is powering them both, from 1 power supply. Pretty neat, right? Again, necessity is the mother of inventions !
Here is a movie with it, a bit long(13min) :

I will get back to the project I discussed with you in a very short while.

 

[marconi]

I have been re-reading the datasheet on the LM3914 because I have been wondering whether it and its associated circuitry is oscillating and being unstable - dependent on the number of LEDs illuminated - worse when several LEDs are on or all are on. Do you think it is oscillating or shimmering or the first LED is slow to illuminate?

I wonder whether the 0V rail has a low enough resistance back to the power supply and whether the 0V and 5V supply to the LM3914 at pins 2 and 3 respectively is not decreasing too much as the LED light. You could do some checks on this with your voltmeter and scope.

Also, it is important for all 0V lines for the LM3914 and to items it connects to are all brought together to one point very close to terminal 2 - see Figure 1.

If it was me I would make up some thicker wire jumper leads with crocodile clips andusing these to parallel the 0V run from the PSU to pin 2 to see if it improved matters. And then repeat with another set taking 5V to pin 3.

Is there any disturbance to the illumination of the LEDs when the relays open or close?

https://www.ti.com/lit/ds/symlink/lm3914.pdf?ts=1614700327590&ref_url=https%3A%2F%2Fwww.ti.com%2Fproduct%2FLM3914

Page 18 'Application Hints'-

Three of the most commonly needed precautions for using the LM3914 are shown in the first typical application drawing showing a 0V–5V bar graph meter. The most difficult problem occurs when large LED currents are being drawn, especially in bar graph mode. These currents flowing out of the ground pin cause voltage drops in external wiring, and thus errors and oscillations. Bringing the return wires from signal sources, reference ground and bottom of the resistor string (as illustrated) to a single point very near pin 2 is the best solution. Long wires from VLED to LED anode common can cause oscillations. Depending on the severity of the problem 0.05μF to 2.2μF decoupling capacitors from LED anode common to pin 2 will damp the circuit. If LED anode line wiring is inaccessible, often similar decoupling from pin 1 to pin 2 will be sufficient.

If LED turn ON seems slow (bar mode) or several LEDs light (dot mode), oscillation or excessive noise is usually the problem. In cases where proper wiring and bypassing fail to stop oscillations, V + voltage at pin 3 is usually below suggested limits.

 

[_q12x_]

Thank you mister @marconi. Very interesting what you find ! I must confess, that I did read this pdf a tiny bit. I should give it a full read as you just did now. But the problem is a bit more complicated than this, because alone, unlinked to the RF receiver, does not fluctuate or misbehave. ONLY when is linked (pin5) to the output of the RF receiver circuit after the 555 oscilator, ONLY then, it starts oscilating and random patterns in different times when I freshly connect it. So, it is very stable by it's own, but that particular circuit, with that 555 in it, it just messing it up. I will have to make a movie, showing this erroneous behaviour and explaining what I did ... hopefully as complete as I can and if I even remember all the permutations I did. At least the major ones.
There is an exception. When the 555 circuit is not added to the Rx on the receiver, and pin5 is connected directly to this Rx, all is doing fine, not oscilating, but not working as desired as well. I didnt try your circuit yet since I had to do that other projekt, but I will very soon and I will announce you how it went. Im a bit demoralized by these attempts, but I will get over them.