In some examples, a system comprises a control subsystem comprising a static power supply, a modulated power supply, and a comparator. The system also includes a galvanic isolation device coupled to the static power supply, the modulated power supply, and the comparator. The system further includes a parameter measurement subsystem comprising a parameter measurement device coupled to a capacitor to be charged by the static and modulated power supplies via the galvanic isolation device. The capacitor has an electrical connection to the galvanic isolation device modulated in accordance with a current pulse train output by the parameter measurement device, the current pulse train indicating a parameter measured by the parameter measurement device. The comparator is to produce a signal indicative of the modulated electrical connection between the capacitor and the galvanic isolation device.