This board made to use it with 4X  0-10v ballasts combined with arduino . The main Chip used is  LM324       

1) An RC filter to get an analog output from the PWM signal that Arduino outputs. I have read some information about this kind of filters and it's seems that there is a rule that establish the relation between the time constant of the RC filter and the period of the PWM signal: the RC time contant should be greater than the period. In my case the time constant is 100 times greater.

2) An operational amplifier with a gain of 2 to obtain the output in the range of 0-10V