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BOM: header facts from the carrier spec; realign pull-up 100 kΩ (TXB0108 needs > 50 kΩ)

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Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DDwfd6Ki8UfG4hK6W5YpJz
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Mikkeli Matlock
2026-10-12 15:33:58 +09:00
parent 69669d1832
commit 7b32e06e24
1 changed files with 13 additions and 3 deletions
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docs/BOM.md
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@@ -121,10 +121,19 @@ type: reference
| GND | 6 | | GND | 6 |
| TX | 10 (UART1 RX) | | TX | 10 (UART1 RX) |
| RX | 8 (UART1 TX), needed only to send config commands | | RX | 8 (UART1 TX), needed only to send config commands |
| *Realign button (optional)* | 7 (GPIO09, `PAC.06`) through the button to ground on 9; 10 kΩ from 7 to 3.3 V (pin 1). Pin to confirm | | *Realign button (optional)* | 7 (GPIO09, `PAC.06`) through the button to ground on 9; 100 kΩ from 7 to 3.3 V (pin 1 or 17) |
Everything sits in header pins 1–10, so one 2×5 connector can carry it. Pins 3/5 (I²C bus 7) carry the UPS monitor. Everything sits in header pins 1–10, so one 2×5 connector can carry it. Pins 3/5 (I²C bus 7) carry the UPS monitor.
Header facts (carrier board spec SP-11324-001 v1.3, Table 3-3 and 5-3; raw copy in `/mnt/wdelem/dropzone/`):
- All signals are 3.3 V. Pins 7, 8 and 10 pass through **TXB0108 level translators**: their outputs are very weak (±20 µA) and can be
overdriven, and **any pull-up or pull-down on them must be weaker than 50 kΩ** (I²C excepted). Hence 100 kΩ for the button, not 10 kΩ.
- 3.3 V on the header: 1 A per pin, but **0.1 A in total** for the header from `VDD_3V3_SYS`. 5 V: 0.5 A in total.
- Pin 8 (UART1 TX) is also a boot strap (`BOOT2_STRAP`): nothing should drive it while the board powers up. The WT61's RX is an input,
so it does not.
- Pin 7 is `PAC.06` (gpiochip0 line 144), pulled down on the module at power-on.
### Notes ### Notes
- **The header is 3.3 V logic and not 5 V tolerant.** Powering the module at 3.3 V keeps every signal at 3.3 V. The datasheet only says - **The header is 3.3 V logic and not 5 V tolerant.** Powering the module at 3.3 V keeps every signal at 3.3 V. The datasheet only says
@@ -145,8 +154,9 @@ Everything sits in header pins 1–10, so one 2×5 connector can carry it. Pins
- **Output is low-pass filtered at 10 Hz** by default, even at 100 Hz output. Fine for vehicle motion, but it smooths out bumps and - **Output is low-pass filtered at 10 Hz** by default, even at 100 Hz output. Fine for vehicle motion, but it smooths out bumps and
vibration. A gyro rate under 0.122 °/s reads as 0 (static threshold). Both are set only from WitMotion's PC software; there is no vibration. A gyro rate under 0.122 °/s reads as 0 (static threshold). Both are set only from WitMotion's PC software; there is no
serial command for them. serial command for them.
- **Realign button parts (optional, not fitted):** one momentary push button (normally open) and one 10 kΩ resistor. The resistor pulls - **Realign button parts (optional, not fitted):** one momentary push button (normally open) and one 100 kΩ resistor. The resistor pulls
pin 7 up to 3.3 V, so the pin reads 1, and a press grounds it to 0. Realigning starts from the tablet app first; the button adds a way pin 7 up to 3.3 V, so the pin reads 1, and a press grounds it to 0. Weak on purpose: the pin sits behind a TXB0108 (see header facts);
check both states with `gpioget` once wired. Realigning starts from the tablet app first; the button adds a way
that works without the tablet, triggering the same command. that works without the tablet, triggering the same command.
- **Realign:** a press levels the frame to gravity (the mounting rotation, from averaged accelerometer readings) and sends - **Realign:** a press levels the frame to gravity (the mounting rotation, from averaged accelerometer readings) and sends
`FF AA 52` to zero yaw. The result is stored on disk, not redone every drive. Refuse while moving (gyro or GPS speed); record raw data `FF AA 52` to zero yaw. The result is stored on disk, not redone every drive. Refuse while moving (gyro or GPS speed); record raw data