TomGeorge:
Hi, I noticed this long drawn out discussion, here is my bit, find in the attached schematic that if you use a zener diode in series with the input to the opto, the input will not conduct until the input is above the zener voltage.
Using 10mA as the starting current is just a suggestion.
Just some quick calcs and you don't need high wattage components. It will need some more work to check current at 80V, but hey there's the challenge.
A lot of industrial CNC and other control equipment use this method to check if all the supply rails in its system are present before commencing and continuing any sequence.
Tom thank you very much for your suggestion also, as well as dc42, you have helped me a lot to understand all this.
I have actually build your suggestion but using 2 zener diodes as I couldnt get 55V zeners plus this way I get double power dissipation as each of them has 1/2 the voltage.
Things get warm but just that, and optocouplers are sending the signal completely correct to the arduino! great !
It is also a very good improvement having the 55V trigger instead of just allowing voltage to build up until the 4N25 activated. This way I can detect ON/OFF states much more precisely.
Thanks !!
I attached my unfinished PCB, although the part we are discussing here is indeed completed. I included a onboard led to show the status of each input. any suggestion on improvement is of course welcome
