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Wiring the Alarm Signal of Brushless Driver

This article will introduce the alarm signal wiring of our StepperOnline brushless driver.


  1. Description of Alarm Signal Characteristics


Output Type: NPN Open Collector Output (Sinking Output)

Signal Level:


  • Alarm State (ALM ON): The output terminal is conducting to 0V (GND) (equivalent output ≈ 0V, low level)


  • Normal State (ALM OFF): The output terminal is floating/high impedance (≈5V is provided by an external pull-up resistor, high level)


  1. Wiring Diagram for Relay (5VDC) Connection with Brushless Driver



When the brushless driver operates normally, relay K02 remains de-energized. When the driver detects an alarm condition, relay K02 will activate.


  1. Precautions


3.1. Relay Polarity Must Be Correct


The relay should be placed between the power supply (+V) and the ALM output (current path: +V → Relay → ALM → GND).


3.2. Pay Attention to the Relay's Rated Voltage


  • For a 5VDC relay, connect the positive terminal to the +5V interface and the negative terminal to the ALM interface (as shown in the diagram above).


  • If using a 12VDC or 24VDC relay, an additional 12VDC or 24VDC power supply is required. Refer to the wiring diagram below for details.



3.3. Signal Anti-Interference Design


  • For cable lengths >1m: Use twisted-pair shielded cable, with the shield grounded to the driver’s GND at one end only.


  • In high-noise environments: Parallel a 10kΩ resistor between ALM_OUT and GND (to prevent false triggering from static electricity); Parallel a 0.1μF capacitor across the relay coil (to suppress contact bounce).


  1. Summary


The alarm signal (ALM) of StepperOnline brushless drivers is an NPN open-drain output (active-low), requiring an external pull-up (typically provided by the relay coil) to maintain a high level in the normal state.


When driving a relay:


  • Always connect the relay between the power supply (+V) and ALM.


  • Ensure the relay voltage matches the power supply (use an independent power supply for non-5V relays).


  • In long-distance wiring or noisy environments, strictly follow shielding and RC anti-interference measures to ensure signal reliability.





Updated on: 01/07/2025

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