OK. Now I understand.
Setpoint was previously read via ACDin (0-1023).
ADValue was scaled in pulses per 100ms (approx 0-550)

In the new setup, variable NewCount (replacing ADValue) can range from 0-255 so I propose to convert the ADCin result from 10-bit to 8-bit
Setpoint = Setpoint>>2
so that the error term does not get too large and gain terms can be kept to a manageable size.

I will let you know how things pan out after tonight's round of experimants.

Cheers
Barry
VK2XBP