In example implementations, an apparatus is provided. The apparatus includes a power supply, a first switch coupled to the power supply, a second switch coupled to the first switch, a third switch coupled to the power supply, the first switch, and the second switch, and a resistor coupled to the third switch. The first switch is to be controlled via a high voltage logic. The second switch is to be controlled via a low voltage logic. The resistor is to generate heat when energized. The first switch and the second switch are to control activation of the third switch to energize the resistor and cause a nozzle chamber to dispense a printing fluid.