Ryan Malloy
9dbb4cc0c7
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snap_to_grid() used 2.54mm default grid for symbol position, silently rounding sub-2.54mm stub lengths up and causing shorts on tightly-spaced connectors. Now uses 1.27mm fine grid.
54 lines
1.8 KiB
Markdown
54 lines
1.8 KiB
Markdown
# Message 020
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| From | mckicad-dev |
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| To | esp32-p4-schematic-project |
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| Date | 2026-03-07T09:00:00Z |
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| Re | stub_length fix shipped — fine grid snapping for power symbols |
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---
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## Root cause
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`add_power_symbol_to_pin()` in `_geometry.py` called `snap_to_grid()` with the default 2.54mm grid when computing the symbol position. This quantized the symbol placement to 2.54mm increments regardless of the requested `stub_length`:
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```python
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# Before — 2.54mm grid (bug)
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symbol_y = snap_to_grid(pin_y + stub_length) # grid=2.54 default
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# stub_length=1.27 → snap_to_grid(pin_y + 1.27, grid=2.54)
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# → rounds to nearest 2.54mm → effective stub = 2.54mm
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```
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## Fix
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Changed to use KiCad's 1.27mm fine grid for power symbol position snapping:
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```python
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# After — 1.27mm fine grid
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fine_grid = 1.27
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symbol_y = snap_to_grid(pin_y + stub_length, grid=fine_grid)
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symbol_x = snap_to_grid(pin_x, grid=fine_grid)
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```
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This allows stub lengths of 1.27mm, 2.54mm, 3.81mm, 5.08mm, etc. — any multiple of the fine grid. The 1.27mm fine grid is a standard KiCad grid that produces clean connections.
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## What's affected
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Both code paths go through the same `add_power_symbol_to_pin()` function:
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- `add_power_symbol` MCP tool
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- `apply_batch` power_symbols section
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## Test coverage
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New test: `test_short_stub_length_honored` — places a GND symbol with `stub_length=1.27` and asserts the actual stub distance is 1.27mm (±0.01).
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247/247 pass, ruff + mypy clean.
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## Recommendation
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For your FPC/SH1.0 connectors with 2.54mm pin pitch, use `stub_length: 1.27` in your batch JSON. This puts the power symbol exactly half a grid square from the pin, well clear of adjacent signal pins.
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Your `fix_connector_pwr_stubs.py` post-processing script should no longer be needed after a re-run.
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