How does the microprocessor control the relays on the relay board?

The microprocessor controls the relays on the relay board by providing a ground path for the relay coil. In relay systems, when the microprocessor activates a relay, it typically does so by completing a circuit, allowing current to flow through the relay coil. This action creates a magnetic field that closes the relay contacts, thereby controlling the connected load.

Providing a ground path is a common method used in microprocessor-controlled systems, especially since many relays are designed to be activated by applying a positive voltage to one side of the coil while connecting the other side to ground. This arrangement allows the microprocessor to switch various loads on and off effectively by controlling the grounding signal.

The other options do not accurately describe the typical operation of a microprocessor in relation to relays. For instance, sending a 12 Vdc signal would be relevant for relays specifically designed for that voltage, but it's not the method of control. A low voltage AC control signal also does not fit the operational standard for most microprocessor-controlled relay functions, which rely on DC signals for control. Thus, providing a ground path is the most accurate and commonly employed method for relay activation in microprocessor systems.