How to Use Digital Outputs to Control a Relay
Digital outputs can be used to control external relays for switching circuits, activating alarms, or controlling other equipment.
Before You Begin
Verify the relay coil current before connecting the relay to the digital output.
Maximum digital output current: 15 mA
Do not connect a relay that draws more than 15 mA directly to the digital output. Exceeding the maximum current rating may damage the device or cause unreliable operation.
Connect a Relay to the Digital Output
To control a relay directly from the digital output:
- Verify that the relay coil current is 15 mA or less.
- Connect the digital output to the relay coil.
- Verify the correct polarity, if applicable.
- Activate the digital output.
- Verify that the relay energizes and switches its contacts as expected.
When the digital output is activated, it energizes the relay coil. The relay then switches its contacts to control the connected circuit.
Connect a Relay That Requires More Than 15 mA
If the relay coil requires more than 15 mA, do not connect it directly to the digital output.
Use a transistor or relay driver module between the digital output and the relay.
In this configuration:
- The digital output controls the transistor or driver module.
- The transistor or driver module supplies the current required by the relay.
- The relay switches the connected circuit without exceeding the digital output's 15 mA rating.
Verify the Installation
Before operating the system, verify that:
- The relay coil current does not exceed 15 mA when connected directly.
- Wiring and polarity are correct.
- A suitable driver is installed if the relay requires more than 15 mA.
- The relay activates and switches correctly when the digital output changes state.