I want to use a Relay module to control the on/off state of my circuit. Do I need to provide an external power supply, or the module itself can supply the voltage for it?
Yes, you need to provide an external power supply. Since the Relay modules just open and close a circuit, you need to provide the external source that will be working with your relay.
The following figure shows a simplified block diagram of the NI 9481. Note how there are no additional processing/connections that the module is doing besides closing the circuit between the CHa and CHb ports of the module.
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