Hello,
I am trying to detect each zero crossing of mains A.C. voltage.
Do i need to use two opto-couplers like what is shown in the circuit or
is there a device that works for both directions. v1 and v3 shown in the
circuit would go to a micro-controller that fires the triac through a diac
which is not shown in the schematic.
Thanks in advance
Joe

 

Hello,

Is it possible to use a transformer for isolation?
Then you could have a look at the following circuit:
http://www.visionics.a.se/Zero-Crossing-Detector1.aspx
Bertus

 

What about PC814?

 

Hello,

An other option would be the H11AA1:
http://www.bristolwatch.com/ele2/zero_crossing.htm
Bertus

 

How about a full wave bridge on U1. If you add the 4 diodes right at U1 they can be low voltage low current. The power line voltage is not at this point the signal is only +/- 1.5 volts.

 

Use a transformer, anywhere from 5 to 12 volts and a full wave bridge rectifier. Couple the output to a gate. Each time the wave goes from zero to V+ you can count that as a single crossing. Keep in mind that with a full wave rectifier you're converting the negative going waveform into a positive going wave form. So each positive waveform is representative of a zero crossing.

Next things we (I)'d like to know:
Why do you want to detect zero crossing?
What frequency are you trying to detect zero crossings?

You DO understand that zero crossings are going to be double the frequency, right?

 

I could but I need to use a microcontroller anyways.

Hello,

Is it possible to use a transformer for isolation?
Then you could have a look at the following circuit:
http://www.visionics.a.se/Zero-Crossing-Detector1.aspx


Bertus

 

Use a transformer, anywhere from 5 to 12 volts and a full wave bridge rectifier. Couple the output to a gate. Each time the wave goes from zero to V+ you can count that as a single crossing. Keep in mind that with a full wave rectifier you're converting the negative going waveform into a positive going wave form. So each positive waveform is representative of a zero crossing.

Next things we (I)'d like to know:
Why do you want to detect zero crossing?
What frequency are you trying to detect zero crossings?

You DO understand that zero crossings are going to be double the frequency, right?

Hello Tony,
I am trying to build a spot welder to make lithium ion battery packs. I want to detect zero crossing then delay some time before firing the triac. It is so I can control the power into the secondary to get a good weld. I also want to count zero crossing edges because I want to control how many cycles get applied to the secondary. I will have to check if my micro can detect both pos and neg going pulses, if so then I just need one opto coupler and my question was moot. I just did not think of it at the time.
Thanks for that.

 

@bertus,
Yes that what I was looking for, a bidirectional opto coupler. Tony gave me an idea ...if my micro pin detects both rising and
falling edges then I can get by with what I have in the parts bin. But this is good to know. Thank you.
Joe

Hello,

An other option would be the H11AA1:
http://www.bristolwatch.com/ele2/zero_crossing.htm
Bertus

 

@ronsimpson
I like that idea Ron. That would work. I have bridges in the parts bin too : )
Thanks
~Joe

How about a full wave bridge on U1. If you add the 4 diodes right at U1 they can be low voltage low current. The power line voltage is not at this point the signal is only +/- 1.5 volts.
View attachment 189516

 

 

View attachment 189534

Do not do this! 230V/2.2k=about 100mA. Increase the resistance greatly.
The diodes must with stand the power line voltage. Put the diodes on the 4N25, (to the right of the resistor) and the diodes will only see 1.5 volts.
Many resistors are only good for 200 volts. I usually use two resistor in series for power line applications.

 

Hello,
I am trying to detect each zero crossing of mains A.C. voltage.
Do i need to use two opto-couplers like what is shown in the circuit or
is there a device that works for both directions. v1 and v3 shown in the
circuit would go to a micro-controller that fires the triac through a diac
which is not shown in the schematic.
Thanks in advance
Joe

There are zero crossing opt couplers. Usually used to control AC mains via a digital control circuit
Is that what you mean?

eT

 

There are zero crossing opt couplers. Usually used to control AC mains via a digital control circuit
Is that what you mean?

eT

Yes, I will output a signal from my microcontroller to a diac - triac circuit that is not shown. I thought I would need to rising edges, one on pos. half cycle, one on the neg half cycle to let the micro know to start counting before turning on the triac. I have not checked yet but if my micro pin can react to both neg and pos going edges then I can use what I have.

 

There are zero crossing opt couplers. Usually used to control AC mains via a digital control circuit
Is that what you mean?

Those opto(s) are nice in that you can turn on the opto any time you want and it will wait until the next zero crossing to actually turn on.

What is wanted is a way for a micro to see the crossing, delay some time, turn on the triac. I am assuming the delay is to create a duty cycle to reduce power.

 

How close to the zero crossing do you want the signal to be generated?

 

Yes, I will output a signal from my microcontroller to a diac - triac circuit that is not shown. I thought I would need to rising edges, one on pos. half cycle, one on the neg half cycle to let the micro know to start counting before turning on the triac. I have not checked yet but if my micro pin can react to both neg and pos going edges then I can use what I have.

What exactly is the micro controlling? Does it really need to know when the sine wave crosses zero if an external chip is doing that?

eT

 

How close to the zero crossing do you want the signal to be generated?

It's not critical. I am trying to control the welding of nickel tabs for making battery packs.

 

What exactly is the micro controlling? Does it really need to know when the sine wave crosses zero if an external chip is doing that?

eT

When the micro gets the zero detectors edge it delays some time then turns on the triac to deliver power to the welding transformer.

 

This is how I did it for my weld pulser.

The mains transformer I used has a secondary voltage of about 6 or 7 volts RMS. The 12 volt zener it to clamp any spikes. It does not conduct with the normal output of the bridge rectifier. The diode D1 is to allow in circuit programming.

Edit. The two errors in the schematic spotted by Ronsimpson in post #21 have now been corrected in the schematic. (I should have also included a fuse in series with the transformer promary before posting it.

Les.