warehack.ing/i-k-bus-board
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Update docs: R2=220 fix, sweep netlists, corrected BOM and drain figures

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Ryan Malloy 2026-02-13 01:02:06 -07:00
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CLAUDE.md
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@ -2,7 +2,7 @@
## Attribution ## Attribution
Circuit design and protocol library based on **[muki01/I-K_Bus](https://github.com/muki01/I-K_Bus)** by [@muki01](https://github.com/muki01), licensed under MIT. Optocoupler schematic, IbusSerial library, E46 command codes, and bus documentation are from that project. Circuit design and protocol library based on **[muki01/I-K_Bus](https://github.com/muki01/I-K_Bus)** by [@muki01](https://github.com/muki01), licensed under MIT. Optocoupler schematic, IbusSerial library, E46 command codes, and bus documentation are from that project. **R2 modified from 470Ω to 220Ω** for 3.3V ESP32 compatibility (original design targets 5V Arduino).
## Project Overview ## Project Overview
@ -89,7 +89,7 @@ Bridges the bus-side 12V to the MCU-side 12V rail. This powers the MCU (via a 3.
| Ref | Value | Package | Qty | Notes | | Ref | Value | Package | Qty | Notes |
|-----|-------|---------|-----|-------| |-----|-------|---------|-----|-------|
| U1, U2 | PC817 | DIP-4 | 2 | Optocoupler, CTR >= 50% at 5mA | | U1, U2 | PC817A+ | DIP-4 | 2 | Optocoupler, any grade (A/B/C/D). PC817A works; B+ adds margin |
| Q1 | BC547 | TO-92 | 1 | Or 2N3904 — TX LED driver | | Q1 | BC547 | TO-92 | 1 | Or 2N3904 — TX LED driver |
| R1 | 2k | 0805/TH | 1 | RX LED current limiter | | R1 | 2k | 0805/TH | 1 | RX LED current limiter |
| R2 | 220 | 0805/TH | 1 | TX LED current limiter (reduced from 470 for 3.3V ESP32) | | R2 | 220 | 0805/TH | 1 | TX LED current limiter (reduced from 470 for 3.3V ESP32) |
@ -247,7 +247,11 @@ mcp__mcp-ltspice__analyze_waveform(raw_file_path, signal_name, analyses)
**Simulated and validated.** Uses LTspice's built-in PC817 subcircuit (from `lib/sub/PC817.sub`) with `Igain=1m` (PC817A, ~100% CTR). Two netlists cover both signal paths: **Simulated and validated.** Uses LTspice's built-in PC817 subcircuit (from `lib/sub/PC817.sub`) with `Igain=1m` (PC817A, ~100% CTR). Two netlists cover both signal paths:
- `reference/ibus_rx_path.cir` — RX path: bus byte 0x50 at 9600 baud → U1 PC817 → ESP32 RX - `reference/ibus_rx_path.cir` — RX path: bus byte 0x50 at 9600 baud → U1 PC817 → ESP32 RX
- `reference/ibus_tx_path.cir` — TX path: ESP32 TX → Q1 BC547B → U2 PC817 → bus (with RX loopback) - `reference/ibus_tx_path.cir` — TX path: ESP32 TX → Q1 BC547B → U2 PC817 → bus (R2=220Ω, with RX loopback)
- `reference/tx_validated_r2_220.cir` — TX validation at worst-case bus loading (1kΩ pull-up)
- `reference/tx_sweep_r2.cir` — R2 sweep (100–470Ω) at worst-case CTR
- `reference/tx_sweep_rpull.cir` — Bus impedance sweep (510Ω–10kΩ)
- `reference/tx_sweep_ctr.cir` — CTR grade sweep (PC817A through PC817D)
**PC817 SPICE pin order:** `1=Anode, 2=Cathode, 3=Collector, 4=Emitter` — subcircuit uses a VCCS (G1) with `{Igain}` parameter to model optical coupling. **PC817 SPICE pin order:** `1=Anode, 2=Cathode, 3=Collector, 4=Emitter` — subcircuit uses a VCCS (G1) with `{Igain}` parameter to model optical coupling.
@ -307,7 +311,8 @@ The repo includes an extensive documentation collection (`Docs/`):
2. Protocol differences documented (vs OBD-II K-line for Tucker project) 2. Protocol differences documented (vs OBD-II K-line for Tucker project)
3. Software reference identified (IbusSerial library, E46 command codes) 3. Software reference identified (IbusSerial library, E46 command codes)
4. Module address map and message format documented 4. Module address map and message format documented
5. **SPICE simulation validated** — both RX and TX paths simulated with LTspice PC817 model at 9600 baud. RX path gives clean 0-3.13V logic at 3.3V VCC. TX path confirms signal inversion and 0.17V bus LOW. Rise/fall times within 9600 baud budget. 5. **SPICE simulation validated** — both RX and TX paths simulated with LTspice PC817 model at 9600 baud. RX path gives clean 0-3.13V logic at 3.3V VCC. TX path confirms signal inversion and 0.27V bus LOW on 1kΩ bus. Rise/fall times within 9600 baud budget.
6. **R2 optimized for 3.3V** — parameter sweeps across R2, bus impedance, and CTR grade identified R2=220Ω (down from 470Ω) as the fix for 3.3V ESP32. Doubles LED drive current to 9.71mA, supports bus pull-ups down to ~530Ω.
## What's Next ## What's Next
@ -323,4 +328,4 @@ The repo includes an extensive documentation collection (`Docs/`):
- The optocoupler isolation protects the ESP32 from the car AND the car from the ESP32. - The optocoupler isolation protects the ESP32 from the car AND the car from the ESP32.
- Sniff bus traffic (RX only) before attempting any TX operations. - Sniff bus traffic (RX only) before attempting any TX operations.
- The bus has no authentication — any properly formatted message will be accepted by target modules. Use responsibly. - The bus has no authentication — any properly formatted message will be accepted by target modules. Use responsibly.
- Parasitic drain: the interface draws ~6mA from the bus 12V through R1 and U2. Disconnect or add a sleep circuit for long-term parking. - Parasitic drain: the interface draws ~5.4mA continuously from the bus 12V through R1 (RX LED always on when bus is idle). U2 LED only draws current during TX (~9.7mA pulses). Disconnect or add a sleep circuit for long-term parking.