To convert a 3-wire Hall sensor to work with a 2-wire inductive (Variable Reluctance/VR) input on a CDI, you must transform a digital square wave into an analog-style pulse. This is significantly more complex than the reverse because most 2-wire CDIs (like older Saito units) expect an AC signal that crosses zero volts to trigger the ignition.
Conversion Options
1. Professional Signal Converter (Recommended)
The most reliable method is to use a dedicated signal converter designed for motorsport. These units are built to take a Hall effect signal and output a simulated inductive pulse that your CDI can understand.

• KMS Hall & Inductive Converter: This device from Kronenburg Management Systems (KMS) is specifically designed to convert Hall sensor signals into inductive signals for ECUs and ignition systems.
• Speedway / Motorsport Converters: Look for "Hall-to-VR" or "Digital-to-Analog tachometer converters" from specialized retailers like Summit Racing.

2. The Capacitor Coupling Method (DIY)
If you want to build a simple interface, you can try "AC coupling" the Hall signal. This tricks the CDI by turning the Hall sensor's 0-5V square wave into a brief positive and negative spike.
Components needed:

• 10k \(\Omega \) Resistor: Pull-up for the Hall sensor.
• 0.1µF to 1µF Capacitor (Non-polarized): Blocks DC and passes only the "edges" of the signal.

Wiring:

1. Hall Sensor Power: Connect Red to +5V and Black to Ground.
2. Pull-up: Connect the 10k \(\Omega \) resistor between +5V and the Hall Signal wire (White/Yellow).
3. The Converter: Connect one leg of the Capacitor to the Hall Signal wire.
4. To CDI:
   • Connect the other leg of the capacitor to one of the CDI's trigger inputs.
   • Connect the other CDI trigger input to Common Ground.

3. Important Considerations

• Signal Strength: Some 2-wire CDIs require a high-voltage pulse (several volts) to trigger. A 5V Hall signal through a capacitor might be too weak. If it doesn't fire, you may need a small transformer or an op-amp circuit to boost the spike.
• Timing Shift: Converting signals can introduce a tiny delay or shift the trigger point (rising edge vs. falling edge). Always re-check your ignition timing with a strobe light after making this conversion.
• Polarity: If the engine doesn't start, swap the two wires going into the CDI trigger input. Inductive inputs are sensitive to the direction of

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