which breakout board do you have ?
a photo or link will help to find out what type of input the BOB has

going by your photo of the opto-isolator board it looks like the opto-isolators photo transistor collector is connected to the output terminal (U1, U2 ,U3 ,U4 ) via a resistor
the photos resolution is too low to read the value

can you either post a photo that shows the 3 numbers printed on the resistors or just say what the resistors are in your reply

John