It is configured for 15v and 7v max depending on the jumper placement. If you have the board oriented so the text is the correct way for reading, if you place the jumper over the middle and bottom pins, it is for 15v applications. If you place the jumper over the top and middle pins, it is for 7v operations. If you want to cutomize it, then use R17 for channel 1, R18 for channel 2, R19 for channel 3, and R20 for channel 4.
To calculate for custom voltages, you need to usewhere (550 || R17) is the resistor you put in the empty R17 place in parallel with a 550ohm resistor.Code:1.6 = (Wanted Voltage) * (66/(550 || R17))