Digital PWM Signal Converter
(Digital PWM to Analog 0–10V for VFD Control)
Some CNC controllers output a digital PWM signal that is not directly compatible with the analog 0–10V input required by our VFDs. In these cases, a Digital PWM Signal Converter is used to translate that digital signal into a clean analog voltage the VFD can understand.
This article explains how to wire the converter, what to expect, and how to fine-tune it for best results.
When Do You Need a Digital PWM Converter?
You may need a converter if:
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Your controller outputs digital PWM only, not true 0–10V analog
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Your VFD does not respond correctly to spindle speed commands
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RPMs do not match what the controller is commanding
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The spindle speed behaves inconsistently or maxes out early
This is common on many hobby-level controllers.
Wiring the Converter to the VFD
The converter requires power from the VFD to operate. Three wires connect from the converter to the VFD:
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Orange → +10V
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Red → VF1 (Analog Speed Input)
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Black → GND
These connections provide reference voltage, signal output, and ground.
Wiring the Converter Itself
The converter module comes prewired internally. No internal wiring changes are required.
The converter should be mounted close to the controller to keep signal wires short and reduce noise.
Wiring the Converter to Your CNC Controller
Two wires exit the converter for the controller-side connection:
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Red → PWM Signal Output from Controller
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Black → Ground
These wires are intentionally short and should connect directly to the controller’s PWM output and ground reference.
Dialing In Accurate RPMs
Because digital PWM signals vary in quality and voltage range between controllers, fine tuning is usually required.
Inside the converter’s 3D-printed enclosure is a small blue trim potentiometer with a brass adjustment screw.
Adjustment Process
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Power on the VFD and CNC controller
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Command a known RPM from your controller
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Observe the RPM displayed on the VFD
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Turn the brass screw slowly:
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Clockwise or counter-clockwise
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Watch the VFD RPM change in real time
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If RPM moves farther away from the commanded value, turn the screw in the opposite direction
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Continue until the VFD RPM closely matches the controller’s commanded RPM
Take small adjustments and allow the display to stabilize between changes.
Expected Accuracy and Limitations
Digital-to-analog conversion is inherently imperfect. Even when tuned correctly, it is normal to see:
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10–15% variance between commanded RPM and actual RPM
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Slight drift at very low or very high RPM ranges
This is expected behavior and does not indicate a faulty converter or VFD.
For applications requiring extremely precise RPM control, a true analog 0–10V output or Modbus control may be a better option.
Key Takeaways
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The converter bridges the gap between digital PWM controllers and analog VFD inputs
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Wiring is straightforward and requires no internal modification
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Fine tuning is normal and expected
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Minor RPM variance is acceptable and common in hobby CNC setups
Need Help?
If you’re unsure whether your controller needs a digital PWM converter, or you’re struggling to get stable RPM control, contact support and include:
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Your controller model
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VFD model
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Photos of wiring
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A short video showing the RPM mismatch, if possible
