Corrupted Sine wave on zeroo crossing

[varooshan]

Corrupted Sine wave on zero crossing

:? searching for an easy and efficient circuit to clean up corrupted sine wave 240Vac 50Hz. Pic 16f87 cannot find the zero crossing.
any help from you guys will be much appreciated
thanks
varooshan

 

[betwixt]

Depends on the type of corruption but a good starting place would be a low pass filter. Beware that it might cause some phase shifting but you can compensate for that in software.

Brian.

 

[varooshan]

Re: Corrupted Sine wave on zero crossing

Depends on the type of corruption but a good starting place would be a low pass filter. Beware that it might cause some phase shifting but you can compensate for that in software.

Brian.

Thanks Brian
my problem is corrupted 50Hz sine wave is superimposed with harmonic of 5th order and pic 16f87 cannot find the zero crossing. where to connect the low pass filter before zero crossing pin?
at the moment there is a 220k resistor from active line to the zero crossing pin. I was thinking to insert the LP
one side to active line and the other side connected to 220K resistor and the other side of the resistor to ZC PIN
What you think?

 

[IanP]

How do you know it’s the 5th harmonic? Do you have any evidence for that?
Maybe a small cap of, say, 1nF can solve your problem ..

IanP
:wink:

 

[betwixt]

Can you post a schematic so we can see how you have it connected at the moment. IanP's solution will probably work but you might be able to get even better filtering by using other components.

Brian.

 

[varooshan]

How do you know it’s the 5th harmonic? Do you have any evidence for that?
Maybe a small cap of, say, 1nF can solve your problem ..

IanP
:wink:

Hi IanP
The noise is round about 250Hz superimposing with 50Hz sine wave. 1nF capacitor connected to zero crossing pin to ground?
Thanks

 

[varooshan]

Can you post a schematic so we can see how you have it connected at the moment. IanP's solution will probably work but you might be able to get even better filtering by using other components.

Brian.

Here is The schematic circuit https://obrazki.elektroda.pl/57_1289697507.jpg



Thanks
varooshan

---------- Post added at 02:22 ---------- Previous post was at 02:16 ----------

Here is The schematic circuit https://obrazki.elektroda.pl/57_1289697507.jpg



Thanks
varooshan

https://obrazki.elektroda.pl/57_1289697507.jpg

 

[Siniša]

Just 1nF will not work if you really have 250Hz on top of 50Hz. I would assume that 250Hz amplitude is significant enough to throw off your 0 detection. You could do it in software, but it would require some work to build some virtual PLL. Other option would be active analog filter, but same as with any filter you'd have to be mindful of phase shift it may introduce.
You could investigate why do you have 250Hz interference in the first place and solve problem at it's source, perhaps bad PCB routing?

 

[varooshan]

Hi Sini
Thank you for your Info. I think the best way is to design bridge rectifier circuit with npn and pnp transistor connected to zero crossing pin. What is your advise
much appreciated?.
Thanks
Varooshan

 

[betwixt]

That's a strange design! It is drawn in a confusing way and the load (the lamp I assume) never seems to have anything fed to it.

What is the supply line (at the top of the schematic), is it the source of the 250Hz?

Brian.

 

[varooshan]

This is one of my old design, the source is 240Vac 50Hz dimmer circuit.
much appreciated

 

[Siniša]

I am not sure how bridge rectifier and transistors could remove 250Hz interference you have problem with? You could try lowering input impedance of your detection input by placing resistor across line and neutral at point where you sample input voltage. Something to draw 1-2mA or maybe even lower might do a trick, if 250Hz injected current is very low. I am still not clear where is this 250Hz coming from? Is it present if you remove lamp? Is it coming from line even before you attach circuit to it? How did you measure this, did you use oscilloscope?