ok ok...
I have done an update.
Better now?

Any reason despite being a smaller circuit, you have gone away from the opto isolator that was recommended ?

 

Any reason despite being a smaller circuit, you have gone away from the opto isolator that was recommended ?

You have recommend me the opto, others have recommended me the voltage divider... As a first try I have chosen something I was more familiar with. Don't take it personal... I have said that I will try the opto solution too...

 

You have recommend me the opto, others have recommended me the voltage divider... As a first try I have chosen something I was more familiar with. Don't take it personal... I have said that I will try the opto solution too...

Thank you
Good luck

 

Thank you
Good luck

In this last revision I've opted for a buck module and a linear one to avoide switching noise and because I want to use this board with 12V and 15V input.
I have also used an opto to avoid the trimmer.
It should work just fine, do you agree? I will try this circuit soon.
Thanks

 

In this last revision I've opted for a buck module and a linear one to avoide switching noise and because I want to use this board with 12V and 15V input.
I have also used an opto to avoid the trimmer.
It should work just fine, do you agree? I will try this circuit soon.
Thanks

Double check what output pins you are using for the 4N35 opto

 

Double check what output pins you are using for the 4N35 opto

nice catch.
other than that, do you think this circuit is ok?
in my board the grounds of the opto are the same.
I lose the purpose of the opto but it should do the job, right?

 

hi LL,
What is the Signal1 input line connected too.?
E

 

hi LL,
What is the Signal1 input line connected too.?
E

it's connected to the main unit of the alarm system. In some unit it is 14.6V high signal in others 12V. From the main unit I get the power for my board too.

 

hi LL,
The original circuit post #2, will work OK.
This is a sim showing Signal from 10V thru 50v, all the parameters are well within specification.
E

 

hi LL,
The original circuit post #2, will work OK.
This is a sim showing Signal from 10V thru 50v, all the parameters are well within specification.
E

Nice.
So, I see that there are at least 2 school of thought for my board.
p.s. that simulation consider the fact that input pin draws almost no current so that Zener diode can guarantee almost constat voltage, right?

 

hi LL,
You don't need a constant voltage on an IO input pin.
Any voltage above the Vhigh threshold of about +3V is seen as an High Input , the 4.7V Zener will hold the voltage below +5v.
E

 

Nice.
So, I see that there are at least 2 school of thought for my board.
p.s. that simulation consider the fact that input pin draws almost no current so that Zener diode can guarantee almost constat voltage, right?

Two schools of thought ..
That's not bad for a public forum .
Imagine trying to design a camel ..