Im trying to interface a keypad button in a device with a MCU, and they need to be in different circuits, with no shared GND.
This keypad button has 5V DC when not pressed, and 0V when pressed. I want to use an optocoupler to "sense" when the button is being pressed (or released) so I can send a signal to an MCU.
But when pressing the button, the amount of current that flows is only 0.5mA. Is this current enough to "turn on" the internal led of an optocoupler, and then it switches the internal transistor?
I tried an ordinary led in series with the keypad button wiring, and although it allows current to pass and the button works, it never lights. The current in the led is even less, it's 0.32mA.
So, if an ordinary led doesn't light, would the optocoupler work?
The optocoupler I have is the 4N25. I can't find if there's a min input current in its datasheet.
If not, is there another way for me to do it?