An UP and a DOWN button control a 32-step digital potentiometer (IC2, AD5228) via the debouncer IC1 (MAX6817). The potentiometer has a power on reset pin which might be tied to ground causing the potentiometer to start at midscale, or to VCC causing it to start at zero scale. The desired function is selectable using jumper JP1. The triac (capable of driving 40A loads) is a bit overkill for the desired power but the BTA41 has an isolated body and therefore handling of the board under voltage is less dangerous as it is with phase on the package. The circuit uses a 68μH inductance, but this might be replaced with a 100 resistor, then replacing the inductance C5 should have a value of 47nF.