zero-crossing

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ZeleC

Joined: 18 Dec 2002
Posts: 296
Helped: 2

29 Sep 2004 9:11 zero crossing optocoupler logic

i m searching for an easy and efficient circuit to detect the zero-crossing of a 240V line so that it can be feed to a microcontroller(i want to control a thyristor)
any help from yu guys will be great
thanks

cozturk

Joined: 02 Apr 2002
Posts: 110

29 Sep 2004 11:58 application note zero crossing detector microchip

You need only 3meg resistor to mcu pin which used in pic12c508 non-isolated dimmer project. Look this.
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1824&appnote=en011013

papyaki

Joined: 13 Apr 2002
Posts: 564
Helped: 19
Location: A small village somewhere in Gaul

29 Sep 2004 12:09 hcpl3700 240v

Hi,

Look at HCPL-3700 optocoupler : h**p://www.fairchildsemi.com/ds/HC/HCPL-3700.pdf

look also this topic : h**p://www.edaboard.com/viewtopic.php?t=58450

* = t

Henrico

Joined: 25 Aug 2004
Posts: 45
Helped: 1

29 Sep 2004 13:07 240v isolated zero cross detection

ZeleC wrote:

Google for MOC 3041 (Motorola).Single chip solution with built in Z/Crossing detection.

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ZeleC

Joined: 18 Dec 2002
Posts: 296
Helped: 2

30 Sep 2004 8:45 hcpl3700 zero crossing

hello
my main object was to transform the sin wave of a ac line phase to a microcontroller in other words when the i have positive it will be logic 1 and when the phase is negative it will be 0 logic , so that i would have a square wave with a freq as same as the AC line (50Hz) coming to the microcontroller , im not seeing a way of doing that with the above ICs
thx you

Taro

Joined: 28 Jun 2001
Posts: 147
Helped: 3

02 Oct 2004 10:02 mains zero crossing schmitt

Dear Zelec
You can make Zero crossing detection many in ways, such as Optoisolate that include Zero-crossing output pin, use NPN transistor get un-filtered signal that come from bridge rectified, etc. But in my opinion I think cozturk's idea is suitable for your demand.

BTW you have to know before that inside PIC'port structure they have diode clamp up to +Vcc and clamp down with GND, so your PIC port is not demaged by 220V voltage. So before use this method, be careful to check your port structure of your microntroller.

Hope it can help
TARO Smile

seven_segment

Joined: 23 Aug 2004
Posts: 44

04 Oct 2004 13:22 mains zero crossing diode

Using an OptoCoupler would probably be the easiest (and safest) solution. Simply keep polling one of your input pins, when the state of the input is reversed (ie logic 1 to 0, or vice versa) you know that zero crossing has just occured. This should be accurate enough, I've done dimming this way without problems.

amraldo

Joined: 29 Aug 2004
Posts: 287
Helped: 25
Location: egypt, cairo

04 Oct 2004 13:54 signal zero crossing detector +microchip

here is a suggestion and it might work:
1-u have to step down the voltage level to an acceptable one (say 5V)
2-use a comparator circuit configuring opamps to produce the logic levels u want.
3-choose the supplies of the comparator propely to produce the required voltage levels representing ur logic levels

ZeleC

Joined: 18 Dec 2002
Posts: 296
Helped: 2

04 Oct 2004 17:45 moc3041motorola

pic is a good idea
but currently im using hc11,
i tried to used a transformer to step down , and then used a couple of buterworth filters and a comparator at the end its working but im having a small problem , the line signal and the one that i got after the comparator are not in phase (~pi/6 difference and not stable sometimes less sometimes greater) a part of this is getting from the transformer some from the filters.
And that is not suitable to control the thyristor because its not the same image as the main line input.

metal

Joined: 21 Dec 2004
Posts: 369
Helped: 13

07 Jan 2005 5:09 zero crossing detection pic

Hello

You can use schmitt-trigger gate to generate clock signals, as long as mains insulation is not important.

A resistor has to be used to reduce the mains voltage.

Anothre thing onmind, search motorola App. Notes, I have downloaded long time ago, it uses logic gate opto-coupler.

Regards

VVV

Joined: 26 Nov 2004
Posts: 1584
Helped: 290

07 Jan 2005 19:29 microchip zerocrossing

I used the voltage from the transformer and fed it directly to a PIC, through a resistor. The PIC input diodes clamp the voltage, the current is limited by the resistor. Got the idea from Microchip's AN521: ww1.microchip.com/downloads/en/AppNotes/00521c.pdf Although, as I said, I did not connect to the AC line directly, but through a 12Vac transformer and a 47K resistor.
Then I wrote a short adjustable delay routine. With that I was able to predict accurately the next zero-crossing. It worked much like a PLL.