Amplify a Khz signal over the mains AC to turn on a LED. Amplify stage

Thread Starter

AlexLPD

Joined Aug 22, 2010
60
Background;
Im making this little circuit to identify a cable in a bundle o f cables, I tried a tracer but dont work. It can point anything beyond 4m. (will make a post latter on).

The main Idea is to send a signal over the Main voltage line, wiring wile its live, and use a pich off wire tool to see if we got the signal on the wire,
after investigate, I found the general Idea, yet my circuit need some tuning.

Main AC = 120Vac peak to peak 60Hz
Injected signal = 5V Peak to peak 10Khz.

This is my circuit;


In the "no kHz signal" I got this readings; Channel Blue is at the output of the attenuator filter and green one is the output at the amplifier stage;



An if I turn on the Khz signal;



So, In the filter of the mains I got a very small voltage even when the circuit is off, there is a way to "center" it to groud to avoid in the real circuit this can be a a positive pulse and trigger the circuit?

If I got a voltage why the led is not turning ON ?
I make the test before to add another amplification stage, a Factor 4 will suit this up?
There a way to "filter" the spikes and make a clean Vcc for the Led to turn ON? I know on that freq, might not be necessary.
Should I try to use an OPAM instead?

Im struggling with the basics, Im not very familiar with the Analog systems.
I will upload the file on proteus.

Thanks for your help and comments.
-Alex.
 

Nykolas

Joined Aug 27, 2013
114
If you google Current carrier communications, Power line communications or modems you should find a lot of useful info. E

PS: The 120VAC line is in RMS, much larger than 120VAC PP.
 

Thread Starter

AlexLPD

Joined Aug 22, 2010
60
If you google Current carrier communications, Power line communications or modems you should find a lot of useful info. E

PS: The 120VAC line is in RMS, much larger than 120VAC PP.
Thanks for the data!
Test I'm not trying to send data per se, just want to trace a wire using a Khz signal, on the proposed circuit any ideas?
 

DickCappels

Joined Aug 21, 2008
5,873
Current carrier communications often use transformers to couple to the AC line. This not only provides a safety advantage but also makes it eaier to reject common mode noise.
 

AnalogKid

Joined Aug 1, 2013
8,099
What you are describing is called a Fox and Hound circuit. For guidance, you can find schematics on the web.

ak
 

Thread Starter

AlexLPD

Joined Aug 22, 2010
60
Ok after some headaches, I decides the best is to get some serius on the matter,

I just today got my Osciloscope, and yes the right tool in deed, so, Im comited to make this work so, following the logical order;
1.- Signal Generator
2.- Pasive high pass
3.-Amplification circuit.

Thanks to this sites, great and very clear information:
https://electronicsclub.info/555astable.htm
http://www.learnabout-electronics.org/Oscillators/osc44.php

I make an square signal Oscillator using the 555, configure in astable mode, I make a test in 680Hz and works perfectly, sos then I changue the circuit for 58Khz. And I get this slope on one of the sides of the square wave, is the cap? or the impedance on the breadboard?
Should I be worry for loosing some signal?
















On the positive side, the square wave is center on the 0, so the amplification wont be like in the simulation.


Thanks for all the insights.
-Alex.
 

DickCappels

Joined Aug 21, 2008
5,873
You are not loosing much of the signal, and the part that is being lost is harmonics which you receiver circuit will probably reject anyway.

When you make your high pass filters, please consider using pulse transformers to provide isolation from the power line.
 

Thread Starter

AlexLPD

Joined Aug 22, 2010
60
Thanks for the insight I have seen some sort of that transformers on power supplies and stuff, in the immediate future I will buy some of them yet, they took 22 days for arrival.

So, In the mean time;
I saw some videos on YT and they performed the measurements on the mains side using a small transformer, so I hook a small signal transformer Primary: 127VAC - Secondary 6.68VAC.


In this picture, you can see the two transformers, on the right there is the "injector" side. On the right the receiver.


In this picture, the two high pass filters.


In the above picture, the signal injector on the top.



The Low Pass filter performance;
I took the 0.1nf and the 10K values and hook up the circuit, its is performed has expected;



In this measurement The yellow chanel is the T1 secondary voltage, while the second channel is the voltage passing the High pass filter.


So, in the next step, I place the signal injector on behind the passive filter;


So I got a nice signal, behind the filte, a square wave of 1.92V. at 680khz.
This is the signal after the high pass filter;



I reduce the signal to 680Hz but I cant get a stable voltage on the reciver.
I belive this is due the Inductance of the transformers, In the circuits described in the links there is no transformer.

I make a test tomorrow to see, If I can get some signal on the other side.
Best regards.

-Alex.
 
Last edited:

DickCappels

Joined Aug 21, 2008
5,873
50 and 60 Hz transformers are not good performers at high frequencies, in this case it is probably mostly do to eddy current losses in the laminations. That's what I had in mind when I mentioned pulse transformers, but I guess having it in mind didn't help as much as writing it where you can see it. I am sorry I did not mention that.

What is the reasoning behind 680 Hz, which sounds very low for a pulse or carrier frequency?
 

Thread Starter

AlexLPD

Joined Aug 22, 2010
60
50 and 60 Hz transformers are not good performers at high frequencies, in this case it is probably mostly do to eddy current losses in the laminations. That's what I had in mind when I mentioned pulse transformers, but I guess having it in mind didn't help as much as writing it where you can see it. I am sorry I did not mention that.

What is the reasoning behind 680 Hz, which sounds very low for a pulse or carrier frequency?
Hi, well I do made a test with 68khz and it was loss ok the transformer cores, so I believe a slower signal will pass more voltage, I was wrong ....the signal is lost on the transformers impedances, I could try to make it faster but it will be lost due to harmonics rigth?

I have two more approaches to test; a resistor signal divider in a 10:1 relation and the the high pass filter and then the injector, maybe add an amplification stagento the signal injector, to get a signal 10Vpp. (More amplitud Will need to be slower rigth?)

Or use a zero cross detector and two 555 one in astable in 68kz for say something, and the other as astable been trigger by the zero cross detector firing the signal just on the zero. Now I'm thinking 68hkz is a multiple of 60hz, a third test comes to my mind, change the injector frequency for a non multiple of mains.

Also re- reading the post on this matter they seem to use an Inductor / capacitor on the injector side. 10mH and 0.1uF are the values, will dig more in to this.

-Alex.
 

Thread Starter

AlexLPD

Joined Aug 22, 2010
60
After some searching it seem the transformer aproach is not the used on this situations, I search for power line comunication for arduino and clearly its an inductor an a X2 capacitor rated, searching I belive is something like;

https://www.allaboutcircuits.com/textbook/alternating-current/chpt-8/resonant-filters/
On the stage of Parallel Resonant Band-pass Filter.

Yet I cant reach dimensions or values to make some inductors, Already call the two biggest cities near to me, they don´t have off the shelf.

Any tougths?
-Alex.
 

DickCappels

Joined Aug 21, 2008
5,873
I do not mean offense to Arduino users in general but I see a lot of circuits that use questionable practices and some that are downright dangerous, and I attribute those problems to the fact that many Arduino projects on the internet are written by not yet experienced engineers. Often high school and college age kids who are learning as they go.

Maybe we can get some ideas from the ST7540 FSK power line transceiver design. The datasheet is at the bottom of this post. The application note and datasheet are too large to upload but you can get the application note with this link (I think -let me know):
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=2ahUKEwiNoeTj8LzkAhUY3Y8KHXGjAv0QFjAAegQIABAC&url=https://www.st.com/resource/en/application_note/cd00143379.pdf&usg=AOvVaw0rO9sg_SxSjrKyv2GHPdtS

You can get the datasheet from this Mouser web page:
https://www.mouser.com/ProductDetail/STMicroelectronics/ST7540?qs=HG6crFoccqqIr3vGW1QBzg==

Check out figures 7 and 9 of the application note. The signal transformer is VAC T60403-K5024-X044 / Radiohm 69H14-2101

In reply to your earlier question, a higher signal level does not necessarily mean a lower frequency is needed.
 

Thread Starter

AlexLPD

Joined Aug 22, 2010
60
I see in deed that a very detailed and clearly very well designed circuit.

In the top response I was refering to something like this;

http://qqtrading.com.my/data-transceiver-module-kq-130f

Its a small and easy power line comunication device, for Arduino, As you can see its is an Inductor and a Capacitor and even some resistor on the high side coupling signal.

I was trying to make this simple, but it seem I will need the capacitance, I got the above values to test; 10mH and 0.1uF, I got the capacitor, but sadly I cant found the way to calculate the impedance I got access to magnetic wire on one local supplys, but not to the mH (mili or micro Henrys the post dont clarify on this, and for what I read they are usually miss placed).

I even dowload a program call Coil64, but I cant figure it out, My idea it was to use dome wire on a spool over a metal screw. According to the calculate coils and then use the Scope to check for the mH capacity.

Any tougths?
-Alex.
 

DickCappels

Joined Aug 21, 2008
5,873
The metal screw will eat up all the power because of eddy current losses in the metal (I tried that a long time ago). You really need a transformer with a ferrite core or an air core transformer with heck of a lot of turns on it. If you can track down the transformer used in the ST Microelectronics demonstration board you will be way ahead in the game.

You might find this information on common ferrite cores to be helpful:
http://cappels.org/dproj/ledpage/leddrv.htm#Common_Sources_for_Ferrite_Cores
(Note to moderators: This is not intended as site promotion and is relevant to the TS's needs)

Many distributors have pulse transformers that are usable at moderately high frequencies.

What you are doing is not as easy as it looks, so its best to take advantage of what others have done and proven to be useful. Using a Y capacitor or X capacitor would make me uncomfortable because any problem with grounding would make the circuit a little bit dangerous. I have to deal with my un-grounded computer and the grounded electronics projects connected to it almost daily and find it both annoying and quite painful.

I find myself wondering whether one of the faster opto-isolators like the Lite-on 4N25 or the Fairchild/On Semiconductor 6N137M opto-isolators would be up to the job, but unless you have many weeks or months to devote to this project just finding the right transformer would be much better.

However you couple to the AC power line be sure to put safety first. Have a fuse in the circuit, even X and Y capacitors occasionally have shorts and they are meant to be able to clear their own shorts by melting away the shorted portion of metaized plastic film so you would need a choke to diode clipper to protect non-line part of the circuitry from spiking to a high voltage.
 

Thread Starter

AlexLPD

Joined Aug 22, 2010
60
I see your point, It seems there is no more to do here, than expect some components, If I got the chance I migth searh for one or two on a power supply, still this is a good learning exercice.

Thanks.
-Alex.
 

Thread Starter

AlexLPD

Joined Aug 22, 2010
60
Im still on this, the next week arrives an LCR meter, and I try this, even the past week I went to a worksite and a Signal traces like the described above is necessary.

-Alex.
 
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