As I said in my previously edited post I don't think you will have enough ac voltage on the probes to activate the opto. At this point I would try the circuit without the pot and R6 at 10 ohms.
SG

 

The opto has a maximum input of 1.65 volts. Your peak voltage is 2 volts. If you set the trim pot too low, you may have blown the opto Typical voltage for the opto to work is 1.25 volts at 60 ma. The minimum resistance should be 12.5 Ω. 12 or 13 are standard 5% values

 

I would think "setting the voltage" is the wrong way to look at this.
You actually need to set the max current. The rated voltage of an LED is what it drops in operation at the specific current. LEDs are current devices. So the way to go is R = E/I.
Let's use 20mA for the LED. 2VAC = 2x1.4 = 2.8V peak. A typical LED drop is about 1.8V
R = (Max peak volts-LCD drop)/20mA
R =(2.8-1.8)/.020
R=1/.02
R=50ohms.
So use a 47R or 56R.
There is no need for the pot.
And I too think there is no need for the resistor on the output of the opto .

Fiddle with the numbers to suit the opto data.

 

Typical voltage for the opto to work is 1.25 volts at 60 ma

That's actually the max current, typical value from the spec sheet is 10ma. The problem is the TS stated in post #1 that the ac input is 2 volts peak to peak. If that is accurate it only leaves 1 vac peak to work with. A voltage doubler may work.
SG

 

The problem is the TS stated in post #1 that the ac input is 2 volts peak to peak.

Ah, yes.I forgot that and was working on 2VAC.
So a rethink is needed. Why not use a current transformer to generate the signal?
Using the opto will not work if it is only 1V peak.

 

I'm thinking a full wave voltage doubler using germanium diodes will get you about 1.6 volts dc. This should be enough to operate the infrared LED in the opto.
SG

 

The initial voltage is produced by pulsing the MOT using phase shift after the zero cross. The voltage is set just so the pins 3 and 4 can conduct. This voltage i

The 2vac is RMS during a weld.


CH2 is the voltage seen at pins 1 and 2. CH1 is signal seen at pins 3 and 4

 

Is that a simulation or the actual wave forms? Is the circuit working?
SG

 

That is the actual wave form.

 

Then the circuit is working, correct? If so, then what circuit did you use?
SG

 

The circuit is working as required but i wanted to know if i have the pot connected the right way.

 

If it's working then yes the pot is connected correctly. Just to be clear are you saying the circuit was working when first posted but just wanted verification on the design?
SG

 

And does tweaking the pot actually change anything?

 

Hi All,

i have a fairly simple circuit where i need to have control of the AC input voltage. peak to peak at 2vac.

The trim pot controls the voltage to the optocoupler which is fed into a mcrocontroller. Is the attached schematic correct ? Here CS-1 & 2 are input voltage terminals. CS goes into a Microcontroller.
View attachment 168177

Not 100% sure - but some types of carbon track might slowly migrate over long time periods with DC. Sufficient amplitude AC can swamp wiper noise as the pot ages too.

 

If it's working then yes the pot is connected correctly. Just to be clear are you saying the circuit was working when first posted but just wanted verification on the design?
SG

True ! it was working earlier without the pot. Just wanted to know if the trim pot was connected correctly in the schematic.

 

And does tweaking the pot actually change anything?

Was asking for an advise about the pot connection before trying it out.

 

True ! it was working earlier without the pot. Just wanted to know if the trim pot was connected correctly in the schematic.

You asked that, as far as i can see I think no one asked you what do you expect to thange with the pot.