zero cross signal for touch wall switch

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vinok
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Posted by vinok: Fri. Apr 15, 2016 - 11:03 AM
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Dear sir,

 

            I wants to design touch wall switch.   Here i have to use TRIAC and MOC3021. My circuit not has direct neutral. because the neutral connected outer side of LOAD.  

my citcuit just has two terminal ,  LINE and LOAD .  But i need  zero cross signals to triggering the load.So i cant able to give correct reference to get zero cross signal. 

       and also it has self oscillating transformer and bridge rectifier to create 5vdc for microcontroller...

any one help me to get correct zero cross signal without the neutral line on circuit.....   

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valusoft
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Posted by valusoft: Fri. Apr 15, 2016 - 11:19 AM
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I suspect the answer is no, but please show your circuit diagram first. Your description is not clear.

Ross McKenzie ValuSoft Melbourne Australia

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vinok
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Posted by vinok: Mon. Apr 18, 2016 - 07:47 AM
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sir herewith i have attached my circuit.

Here the input signals from microcontroller.

this circuit only has line and load. even though the neutral connected outer side of the load.

But i need zero cross signal for given correct triggering input signal for optodiac...

 

     when load off,   we can easily findout the zero cross signal on this circuit.

    but when load  "on" means  line voltage drop out by load. .... this time how can i get the zercross signal....

 

 

* .docx file deleted and its contents saved as .jpg and entered here. Wasn't that  easier? Moderator *

 

Last Edited: Mon. Apr 18, 2016 - 08:36 AM
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Kartman
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Posted by Kartman: Mon. Apr 18, 2016 - 08:10 AM
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Do you really expect us to read a .docx file?

Use an optocoupler, a bridge rectifier and a resistor. You probably find many examples if you Google zeto cross detector.

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vinok
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Posted by vinok: Tue. Apr 19, 2016 - 05:21 AM (Reply to #4)
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Please note this point...
All zero crossing circuit find from line and neutral.

But I wish to find zero crossing signal from line and before load or other ways.
But dont consider neutral line...

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Brian Fairchild
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Posted by Brian Fairchild: Tue. Apr 19, 2016 - 06:52 AM
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vinok wrote:

All zero crossing circuit find from line and neutral. But I wish to find zero crossing signal from line and before load or other ways. But dont consider neutral line.

 

What you describe is quite common. Consider...

 

a) at power-up the triac is OFF and you can detect the zero-crossing because you have a connection directly to LINE and to NEUTRAL via the load.

b) you detect the zero-crossing and turn on the Triac.

c) the Triac now 'short-circuits' the input to your detector.

d) you remove the Triac drive signal as soon as the Triac is ON. The Triac stays on because of the current flowing through it.

e) at the end of the mains cycle the Triac will turn OFF when the current flow falls below the holding current.

f) you are now back at a)

 

Many domestic wall dimmers have this connection arrangement with only two wires. They specify a minimum wattage for the connected load because they rely on enough load current flowing to hold the Triac in the ON condition at step d).

#1 Hardware Problem? https://www.avrfreaks.net/forum/...

#2 Hardware Problem? Read AVR042.

#3 All grounds are not created equal

#4 Have you proved your chip is running at xxMHz?

#5 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

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stevech
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Posted by stevech: Tue. Apr 19, 2016 - 07:11 AM
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Use a solid state relay module. Simple. Cheap. Fire code friendly.

TTL logic level of 5mA DC switches a 20AMP mains circuit.

 

I've used that many times.

 

But if this is a professor's assignment, use my suggestion only for extra credit. And pass on my name to the prof.

I'll look it up for you.

http://www.ebay.com/sch/i.html?_...

 

Last Edited: Tue. Apr 19, 2016 - 07:12 AM
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vinok
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Posted by vinok: Tue. Apr 19, 2016 - 11:52 AM (Reply to #6)
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Thank you for your reply....
When triac off , I can easily find zero cross signal.
But when triac on, here the zero crossing circuit produce some unwanted pulse. But from your thought it will be in zero voltage . How can I neglect this unwanted signal whenever load is on. Here I have to use moc3021 and 200ohm resistor for gate triggering. And triac is bta16 600b.
Please reply me ..

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cts_casemod
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Posted by cts_casemod: Tue. Apr 19, 2016 - 12:12 PM
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If you dont have Neutral, you need to recreate it.

 

If the load is always the same (a light bulb, for example) add a small resistor in series with your load, to drop 1 or 2V under full load. The voltage drop across it is AC so you can easily find the zero cross.

If you wish to go fancier or for variable loads use a hall sensor to measure the AC current, and from there find the zero crossing.

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Kartman
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Posted by Kartman: Tue. Apr 19, 2016 - 12:16 PM
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How can the zero cross detector generate a pulse if the triac is on? There will ve around a 2V drop across the triac, so your zx detector needs to ignore that. You trigger the triac a minimum of around 500us after zx and turn off around 500us before zx.

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vinok
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Posted by vinok: Tue. Apr 19, 2016 - 01:27 PM
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Sir
Here I have to use moc3021. The gate of triac connected with 200ohm and secondary side of moc3021. So when load on, the voltage drop across the triac bta16 600b is around 10v. So I saw this voltage on zerocross signal. But I need 0v on this time.

Anyone please give me correct triac triggering circuit using moc3021 or anyway and zerocross signal circuit.

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Brian Fairchild
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Posted by Brian Fairchild: Tue. Apr 19, 2016 - 03:13 PM
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vinok wrote:

...I have to use moc3021...

 

Why?

#1 Hardware Problem? https://www.avrfreaks.net/forum/...

#2 Hardware Problem? Read AVR042.

#3 All grounds are not created equal

#4 Have you proved your chip is running at xxMHz?

#5 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

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vinok
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Posted by vinok: Wed. Apr 20, 2016 - 05:03 AM (Reply to #12)
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Dear brain fairchild

         Here i need isolation between controller and TRIAC so here i have to use optodiac( moc3021) for further isolation.   

primary side of opto diac connected with controller, 

Based upon the controller's output signal here we can easily control the TRIAC ....

 

 

       from your thought, when main supply will be ON,  The across triac terminals of MT1 and MT2 has no voltage. because it 

will be in short.    so   at the time the output of zero cross not produce any signal.   

But my question  is 

    when load on, some minimum voltage is drop on across triac terminal based on secondary side of optodiac moc3021 and

resistor, this time i get some signals on zerocross output.  

         My controller always detect raising and falling edge of zerocross signal, and based on this signal, it gives correct triggering pulse for primary 

side of optodiac.   when TRIAC off means , no problems yet on this process.

                             but TRIAC ON Means , Minimum voltage drop across also detected by zerocross circuit and based on this signal controller 

generate wrong triggering pulse,   how can i neglate this signal .....    because you know my circuit has two line, so i had this problem..........

 

reply me,.....

 

 

 

 

 

 

          

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valusoft
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Posted by valusoft: Wed. Apr 20, 2016 - 06:04 AM
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vinok wrote:

Dear brain fairchild      

 

Never a truer word said...

 

Ross McKenzie ValuSoft Melbourne Australia

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Brian Fairchild
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Posted by Brian Fairchild: Wed. Apr 20, 2016 - 06:17 AM
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vinok wrote:

Here i need isolation between controller and TRIAC so here i have to use optodiac( moc3021)...

 

So why not use the MOC3041 which has built-in ZVS?

#1 Hardware Problem? https://www.avrfreaks.net/forum/...

#2 Hardware Problem? Read AVR042.

#3 All grounds are not created equal

#4 Have you proved your chip is running at xxMHz?

#5 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

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vinok
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Posted by vinok: Thu. Apr 21, 2016 - 03:20 PM (Reply to #15)
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Sir

Thank you for your suggestions. ..
Moc3041 working well compare with moc3021 because its inbuilt zerocross..

When I was connected bulb and zero watt bulb means the load across phase cycle of positive and negative has same cycle...

But when I connect inductive load of cfl light means positive and negative cycle has different shape... so it makes small flickering on light. How can I overcome it...

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vinok
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Posted by vinok: Thu. Apr 21, 2016 - 03:40 PM (Reply to #16)
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Brian Fairchild
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Posted by Brian Fairchild: Thu. Apr 21, 2016 - 03:45 PM
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vinok wrote:

...when I connect inductive load of cfl light...

 

This is where it gets complicated. Ideally, you need a circuit where you turn the Triac on when the line VOLTAGE does a zero-crossing but off when you get a zero-crossing of the line CURRENT. Many domestic electronic wall switches get around this by specifying that a minimum resistive load must be used alongside any capacitive or inductive loads so as to swamp the reactive current component.

 

You could try a snubber but I doubt it'll work.

 

To do it properly you will need need to be able to turn off the triac under your control. It is possible to do this although it gets quite complicated. It'd be better to swap to using something like an IGBT as your power switching element. Elektor published a circuit in July/August 2012 which you might want to look at.

#1 Hardware Problem? https://www.avrfreaks.net/forum/...

#2 Hardware Problem? Read AVR042.

#3 All grounds are not created equal

#4 Have you proved your chip is running at xxMHz?

#5 "If you think you need floating point to solve the problem then you don't understand the problem. If you really do need floating point then you have a problem you do not understand."

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