I would still try my test now to get a heads up if the opto will work. There are other possible options.

 

It's always worth experimenting with different components to see what works best.

 

Ok, I’ll experiment in the morning
Peter

 

A further thought, I believe the output of the optocoupler will be AC and I guess that will make the relay vibrate, not what I want. So I think I’m back to using diodes but would they be better placed on the sounder input side or the relay output side?
Peter

 

A further thought, I believe the output of the optocoupler will be AC and I guess that will make the relay vibrate, not what I want. So I think I’m back to using diodes but would they be better placed on the sounder input side or the relay output side?
Peter

Thinking about it, I don’t want any voltage drop on the input so the output side would be best.

 

Thinking about it, I don’t want any voltage drop on the input so the output side would be best.

I’ve connected a 10K resistor and the sounder works. I then changed it to 15K and 22K to see how the voltage compares. I think the optocoupler will work. Please see pictures.
Peter

 

I’ve connected a 10K resistor and the sounder works. I then changed it to 15K and 22K to see how the voltage compares. I think the optocoupler will work. Please see pictures.
Peter View attachment 299831View attachment 299832View attachment 299833View attachment 299834

And using the optocoupler with a standard 5v relay and diodes should get me the results required.

 

A further thought, I believe the output of the optocoupler will be AC and I guess that will make the relay vibrate, not what I want. So I think I’m back to using diodes but would they be better placed on the sounder input side or the relay output side?
Peter

Don't need any diodes. The LTV-814 is designed specifically for AC having 2 internal IR LEDs. The input of the relay module requires appx 2ma. The 10K resistor may need to be adjusted.
See what the voltage across the sounder is with a 4.7K resistor.

 

The two LEDs at the input of the LTV-814 full-wave rectify the 50Hz AC which will vibrate the relay at 100Hz.
The relay contacts might even turn on and off at 100Hz making sparks.

 

The two LEDs at the input of the LTV-814 full-wave rectify the 50Hz AC which will vibrate the relay at 100Hz.

It's 2800 hz not 50.

 

It's 2800 hz not 50.

Is this the thread about the piezo sounder?

 

Yes

 

The Optocoupler has arrived and I will experiment tomorrow. I feel that just a basic circuit like this is worth starting with unless I'm missing the obvious, sorry about my drawing!
Peter.

 

The basic circuit failed. Here is my setup. The voltage across the OC when the alarm is triggered is 0.75v AC, obviously not enough. You suggested varying the 10K resistor, what do you recommend I try?
Peter.

 

what do you recommend I try?

4.7K
The OC needs a minimum of appx 1.1 volt.
What relay module are you using?

 

4.7K
The OC needs a minimum of appx 1.1 volt.
What relay module are you using?

Thank you, I’ll try that. Connected is a standard 5v, I also have a 3v but I don’t think that or an isolated one will make any difference.

 

Connected is a standard 5v, I also have a 3v but I don’t think that or an isolated one will make any difference.

It definitely might make a difference depending on the input requirement of the relay module.

 

Junk the optocoupler! use a MOSFET to drive the relay. there is no need for an optocoupler.

 

Junk the optocoupler! use a MOSFET to drive the relay. there is no need for an optocoupler.

Again with no isolation the negative side of the sounder will be connected to the battery negative. Don't know how that will effect the siren as it appears to driven by a transformer.
I believe this schematic is correct for the relay module the TS is using.

 

Where in this thread was that ever mentioned? I must have missed it, which is why I could not make sense of that objection before.