Grounding the drain wire of your Faraday shield to the **negative terminal of the battery** is generally a good approach and should work effectively in most cases. However, there are a few considerations to ensure it doesn't cause issues and provides proper grounding for the shield:
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### 1. **Why Ground the Faraday Shield?**
- The Faraday shield is designed to block external electromagnetic interference (EMI) from affecting the coil and its wiring.
- The drain wire provides a path for any induced currents (from EMI) to be safely diverted to ground, preventing them from interfering with the metal detector's operation.
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### 2. **Grounding to the Battery Negative Terminal**
- Soldering the drain wire to the **negative terminal of the battery** (or the PCB's ground plane connected to the battery negative) is a common and effective method.
- This ensures the shield is at the same potential as the circuit ground, which is necessary for proper operation.
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### 3. **Potential Issues to Consider**
- **Ground Loops**: If the Faraday shield is grounded at multiple points, it can create ground loops, which may introduce noise. Ensure the drain wire is grounded at only one point.
- **High-Frequency Noise**: If your metal detector operates at high frequencies, the grounding point should be as close as possible to the coil's connection to the PCB to minimize inductance in the ground path.
- **Battery Isolation**: If the battery is not isolated from the rest of the circuit (e.g., in a floating system), grounding to the battery negative should not cause issues. However, if the system has a separate ground plane, ensure the battery negative is properly connected to that ground plane.
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### 4. **Best Practices for Grounding the Faraday Shield**
- **Single Ground Point**: Connect the drain wire to a single ground point on the PCB, preferably near the coil's connection point.
- **Short and Direct Connection**: Keep the drain wire as short as possible and route it directly to the ground point to minimize inductance and resistance.
- **Use the PCB Ground Plane**: If the PCB has a ground plane, solder the drain wire to the ground plane near the coil's input. This is often better than connecting directly to the battery terminal.
- **Avoid Floating Grounds**: Ensure the ground point you choose is part of the circuit's reference ground (e.g., battery negative or PCB ground plane).
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### 5. **Testing the Grounding**
- After grounding the shield, test the metal detector for proper operation.
- Check for any increased noise or interference, which could indicate a grounding issue.
- If necessary, experiment with different grounding points to find the one that provides the best performance.
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### Summary
Soldering the drain wire to the **negative terminal of the battery** (or the PCB ground connected to it) is a valid and effective way to ground the Faraday shield. Just ensure the connection is secure, the wire is as short as possible, and there are no ground loops. If the PCB has a ground plane, grounding the shield there (near the coil's connection) is often the best approach.
