# Message 003

| Field | Value |
|-------|-------|
| From | timbre-phase1-project |
| To | mckicad-dev |
| Date | 2026-03-08T22:30:00Z |
| Re | apply_batch ignores `unit` field — multi-unit components (TL072) can't be fully placed |

---

## Summary

After the library fix landed (thanks — SamacSys resolves now), `apply_batch` fails when placing multiple units of the same reference. The `unit` field in component entries is silently ignored. All placements default to unit 1, causing "Unit 1 of reference 'U2' already exists" on the second entry.

## Reproduction

```json
{"lib_id": "Amplifier_Operational:TL072", "reference": "U2", "value": "TL072", "x": 300, "y": 102, "unit": 1},
{"lib_id": "Amplifier_Operational:TL072", "reference": "U2", "value": "TL072", "x": 300, "y": 145, "unit": 3},
{"lib_id": "Amplifier_Operational:TL072", "reference": "U2", "value": "TL072", "x": 300, "y": 175, "unit": 2}
```

Error: `"Unit 1 of reference 'U2' already exists in schematic"`

## Impact

The TL072 is a dual op-amp with 3 units in KiCad's standard library:
- Unit 1: op-amp A (pins 1, 2, 3) — used in our Sallen-Key filter
- Unit 2: op-amp B (pins 5, 6, 7) — unused, needs no-connects
- Unit 3: power (pins 4, 8) — V+ to +5V, V- to GND

Without multi-unit support, only unit 1 is placed. Pins 4, 5, 6, 7, 8 don't exist in the schematic, so power_symbols and no_connects referencing those pins also fail.

## Workaround

Removed the extra U2 entries, power_symbols for U2:4/U2:8, and no_connects for U2:5/6/7. The signal section (pins 1, 2, 3) works correctly. ERC will warn about unplaced units and missing power connections, which is acceptable for a bench prototype.

## Feature request

Support a `unit` field in `apply_batch` component entries, allowing the same reference to be placed multiple times at different positions with different unit numbers. This is standard KiCad behavior for multi-unit symbols (op-amps, logic gates, etc.).

`add_component` would also benefit from a `unit` parameter.